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  • 1. Infant and Child DevelopmentInf. Child. Dev. 18: 271–290 (2009)Published online 18 May 2009 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/icd.624Language and Academic Abilities inChildren with Selective Mutism Matilda E. Nowakowskia, Charles C. Cunninghamb, Angela E. McHolmb, Mary Ann Evansc, Shannon Edisonc, Jeff St. Pierred, Michael H. Boyleb and Louis A. Schmidta,Ã a Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ont., Canada b Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, Ont., Canada c Department of Psychology, University of Guelph, Guelph, Ont., Canada d Child and Parent Resource Institute (CPRI), London, Ont., Canada
  • 2. We examined receptive language and academic abilities in
  • 3. children with selective mutism (SM; n 5 30; M age 5 8.8 years),
  • 4. anxiety disorders (n 5 46; M age 5 9.3 years), and community
  • 5. controls (n 5 27; M age 5 7.8 years). Receptive language and
  • 6. academic abilities were assessed using standardized tests
  • 7. completed in the laboratory. We found a significant group by
  • 8. sex interaction for receptive vocabulary scores such that within
  • 9. females, the SM and mixed anxiety groups had significantly
  • 10. lower receptive vocabulary scores than community controls. We
  • 11. also found that children with SM and children with anxiety
  • 12. disorders had significantly lower mathematics scores than
  • 13. community controls. Despite these differences in mathematics
  • 14. and receptive vocabulary performance, children with SM and
  • 15. children with anxiety disorders still performed at age-level
  • 16. norms, while more children in the community control group
  • 17. performed above age-level norms. Findings suggest that despite
  • 18. their speaking inhibition in the school setting, children with SM
  • 19. are still able to attain the receptive vocabulary and academic
  • 20. abilities that are expected at their age levels. Copyright r 2009
  • 21. John Wiley & Sons, Ltd.Selective mutism (SM) is a disorder in which children fail to speak in certainsituations, usually outside the home, despite speaking normally in othersituations, usually the home (APA, 1994). Although SM is most commonlydiagnosed upon school entry when the demands for children to speak outside ofthe home increase, SM usually first appears in the preschool years (Cunningham,*Correspondence to: Louis A. Schmidt, Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ont., Canada L8S 4K1. E-mail: schmidtl @mcmaster.caCopyright r 2009 John Wiley & Sons, Ltd.
  • 22. 272 M.E. Nowakowski et al.McHolm, Boyle, & Patel, 2004; Steinhausen & Juzi, 1996). The prevalence of SM isestimated at between 0.7% and 2% of children (Bergman, Piacentini, &McCracken, 2002; Elizur & Perednik, 2003; Kopp & Gillberg, 1997; Kumpulainen,Rasanen, Rasska, & Somppi, 1998), with a higher prevalence for immigrantchildren (Elizur & Perednik, 2003). SM is usually more common in girls than inboys with a ratio ranging between 1.2:1 and 2.6:1 (Black & Uhde, 1995; Dummitet al., 1997; Kristensen, 2000; Steinhausen & Juzi, 1996) and often comorbid withother disorders, including anxiety disorders (Bergman et al., 2002; Cunninghamet al., 2004; Cunningham, McHolm, & Boyle, 2006; Dummit et al., 1997; Manassiset al., 2007; Steinhausen & Juzi, 1996; Vecchio & Kearney, 2005; Yeganeh, Beidel, &Turner, 2006; Yeganeh, Beidel, Turner, Pina, & Silverman, 2003), communicationdisorders (Dummit et al., 1997), developmental delay (Elizur & Perednik, 2003;Steinhausen & Juzi, 1996), and oppositional defiant disorder (Steinhausen & Juzi,1996; Yeganeh et al., 2006). However, the aetiology of SM is not well understooddue to the heterogeneous presentation of the disorder, and the fact that it appearsto be influenced by many factors including, genetics, temperament, psychologicalwell-being, attainment of developmental milestones and social factors (Cohan,Price, & Stein, 2006). There is much debate about the conceptualization and classification of SM,which is currently found under the ‘Other Disorders of Childhood’ category inthe Diagnostic and Statistical Manual 4th Edition (APA, 1994). Some researchershave argued that SM should be viewed as a distinct anxiety disorder (Anstendig,1999; Sharp, Sherman, & Gross, 2007; Vecchio & Kearney, 2005) or an extremevariant of social phobia (Yeganeh et al., 2006). This view is supported by simi-larities in the definition of SM and social phobia, both characterized by an intensefear of social situations in which embarrassment may occur as well as a lack ofinhibition and anxiety in the home setting (APA, 1994). As well, a large numberof studies have found that SM co-occurs at high rates with anxiety disorders,especially social phobia. For instance, both Vecchio and Kearney (2005) andDummit et al., (1997) using sample sizes of 15 and 50 respectively, reported that100% of the selectively mute children in their studies met the diagnostic criteriafor social phobia and around 50% of the selectively mute children met the criteriafor a second anxiety disorder. Another study by Black and Uhde (1995) foundthat 97% of the children who were diagnosed with SM met the diagnostic criteriafor social phobia. Longitudinal studies have also found that individuals with a childhoodhistory of SM experienced shyness and symptoms of social anxiety asadults and adolescents despite being ‘cured’ from their SM (Joseph, 1999). Aswell, family studies have found that parents of children with SM havehigher rates of anxiety disorders, especially social phobia (Black & Uhde,1995), compared with parents of normally developing children (Kumpulainen,2002). Numerous researchers (Black & Uhde, 1995; Dummit et al., 1997) have high-lighted the similarities between children with SM and children classified as be-haviourally inhibited. According to Kagan, Reznick, & Snidman (1987), a failureor reluctance to speak is one of the defining characteristics of behavioural in-hibition. Studies have found that parents of children with SM retrospectivelyreport that their children were always shy from their first years of life (Garcia,Freeman, Francis, Miller, & Leonard, 2004). Steinhausen and Juzi (1996) reportedthat 85% of the children with SM in their sample exhibited high levels of shyness.Given that there is evidence that children with behavioural inhibition are at anincreased risk for the development of anxiety disorders (Oberklaid, Sanson,Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 23. Language and Academic Abilities in Children 273Pedlow, & Prior, 1993), many researchers have suggested that behavioural in-hibition may be an early predictor of SM. Despite the similarities in aetiology and presentation between SM and anxietydisorders (especially social phobia), SM differs from anxiety disorders in that it isassociated with higher rates of expressive language difficulties and develop-mental delays. Steinhausen and Juzi (1996) found that 38% of the children withSM in their sample exhibited problems with expressive language, articulation,and stuttering. Similarly, McIness, Fung, Manassis, Fiksenbaum, & Tannockand(2004) reported that compared with children with social anxiety, the speech ofchildren with SM was linguistically simpler and shorter. In terms of generaldevelopmental delays, Kristensen (2000) found that 68% of their sample ofchildren with SM met the criteria for a developmental delay. Thus, difficulties inexpressive language abilities as well as general developmental delays appear tobe distinguishing factors between SM and social phobia. Further research com-paring children with SM to those with anxiety disorders is necessary to betterunderstand the similarities and differences in how the disorders present them-selves and impact children’s functioning. One area of importance in terms of its impact on children’s functioning iswhether SM affects children’s performance in school. Verbal participation atschool is considered an important part of the learning process (Daly & Korinek,1980). Given that SM is characterized by a lack of speech, it is reasonable tosuspect that children with SM may score lower on tests of academic abilities dueto their inability to ask questions when they require clarification. This inabilitymay in turn result in a lack of homework completion and an accumulation ofdeficits due to not receiving the clarification necessary early on and falling be-hind as the material becomes more difficult. As well, much incidental learningoccurs in the school setting through social and collaborative conversations withpeers. Owing to their lack of speech, children with SM may miss out on suchconversations. Past studies investigating academic abilities in children with SM have yieldedvarying results. For example, some researchers have reported that children withSM perform significantly lower than community controls on academic measures(Bergman et al., 2002; Kristensen & Oerbeck, 2006; Schwartz, Freedy, & Sheridan,2006), especially language abilities (Manassis et al., 2007; McInnes et al., 2004). Incomparison, other studies have found no differences between children with SMand community controls (Cunningham et al., 2004). The discrepancies betweenstudies may be explained by three factors: (1) the use of different standardizedmeasures, (2) the utilization of different testing methods such that some studiesrelied on methods that required verbal responses while others used methods thatallowed for non-verbal responses, and (3) different foci of interest in terms ofacademic skill sets. In a sample of 52 children with SM and 52 community controls, Cunninghamet al., (2004) reported no differences between groups on standardized tests of mathand reading or on teacher reports of children’s math, reading, and overall aca-demic abilities. On the other hand, Manassis et al., (2007) recently found thatchildren with SM (n 5 44) performed significantly less well than children withanxiety disorders (n 5 28) and community controls (n 5 19) on a standardized testmeasuring receptive vocabulary abilities. However, a closer look at the groupmeans for the receptive vocabulary standardized scores in this study showed thatchildren with SM tended towards average performance for their age levels,whereas children with anxiety disorders and community controls tended toperform at a higher level. Further, McInnes et al., (2004) investigated a smallCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 24. 274 M.E. Nowakowski et al.sample of seven children with SM and seven children with social phobia. Thechildren’s expressive language abilities were tested by having children retellstories to their parents that they heard in the laboratory and in the home settingand analyzing the content of their narratives. The authors found that, comparedwith the social phobia group, the children with SM had narratives that weresignificantly shorter, less detailed, and linguistically simpler (McInnes et al., 2004). Based on the current literature, it appears that children with SM have lowerreceptive vocabulary and expressive language abilities (although not in theclinical range) but normal math and reading abilities. However, to date, mostresearch (with the exception of Cunningham et al., 2004) has focused on ex-pressive and receptive language abilities. The current study attempted to expandon the past research in three ways. First, we investigated a wide range of aca-demic areas (receptive language, mathematics, reading, and spelling) in onesample. Comparing across previous studies of different academic areas to obtainan understanding of the overall academic performance of children with SM isdifficult given that different researchers may use different criteria to identify theirsamples. Consequently, a study investigating all academic areas in one sampleprovides stronger insight into the academic performance in children with SM.Such insight is important to better formulate treatment methods for these chil-dren. Second, in addition to a control group, we also included a group of childrenwith anxiety disorders as a comparison. With the exception of the study byManassis et al., (2007), no other study has looked across all three groups (SM,anxiety, and control) to determine differences and similarities in academic abil-ities. Third, academic areas other than language have been largely neglected inthe literature on children with SM (notwithstanding Cunningham et al., 2004).Thus, we attempted to look across all academic areas to get a fuller picture ofhow SM affects academic performance. We compared children with SM to chil-dren with anxiety disorders, and community controls on spelling, math, reading,and receptive vocabulary abilities using standardized methods that did not re-quire the children to provide the experimenter with verbal responses. We addressed the following two questions: (1) Do children with SM differfrom children with anxiety disorders, and community controls on standardizedmeasures of reading, math, spelling, and receptive vocabulary abilities? and (2)Given that SM is slightly more common in females than males, are there sexdifferences within and between groups on the standardized measures of aca-demic abilities? Past studies have shown that children with SM perform lower on receptivevocabulary tests compared with children with anxiety disorders and communitycontrols but that these differences are not in the clinical range. Thus, we furtherhypothesized that children with SM would perform lower than children withanxiety disorders and community controls on our measure of receptive voca-bulary ability but that these differences would not be in the clinical range. Giventhe scarcity of research on the performance of children with SM in areas otherthan language, we did not make any specific predictions as to how the threegroups would compare in their performance on standardized measures ofmathematics, spelling, and reading. However, we were interested in investigatingwhether the pattern of lower scores on language tests in children with SM wouldextend to other academic areas. Similarly, given that no past studies have re-ported group by sex interactions in the determination of group differences foracademic performance, we made no specific predictions about possible sex bygroup interactions and rather used the present study as an opportunity to explorepossible interactions.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 25. Language and Academic Abilities in Children 275METHODParticipantsParticipants were 103 children and their parents recruited from local children’smental health agencies. This included one agency that had a regional SMprogramme as well as a Child Database contained in the Department ofPsychology, Neuroscience and Behaviour at McMaster University that comprisesthe names of healthy community children recruited at birth from McMasterUniversity Medical Centre and St. Joseph’s Healthcare, Hamilton, Ontario.Participant demographics are presented in Table 1. All primary caregiverscompleted a package of diagnostic questionnaires (described below) that wasused to determine group membership for the current study. We focused onchildren between the ages of 6 and 10 years old because this is the age range atwhich children with SM are usually first diagnosed (Kumpulainen et al., 1998;Standart & LeCouteur, 2003) and many of the primary caregivers who soughtsupport from the local mental health agency specializing in SM had children inthis age range. Given that we did not want significant age differences betweengroups, we focused our recruitment from the Child Database of normallydeveloping children on the same age range.SM group The inclusion criteria for the SM group were as follows: (1) the primarycaregiver indicated that the child failed to speak (i.e. never talks) in two or moresituations on the Speech Situations Questionnaire—Parent Version (SSQ-Parent;Cunningham et al., 2006; Cunningham et al., 2004) or the teacher indicated thatthe child failed to speak (i.e. never talks) in two or more situations on the SpeechSituations Questionnaire—Teacher version (SSQ-Teacher); (2) the lack of speak-ing was not due to a communication disorder; and (3) the lack of speakingpersisted for a minimum of 1 month. Thus, the SSQ questionnaires completed bythe primary caregiver and teacher were focused on identifying cases of stable,contextual lack of speech in a variety of situations in the general community(parent questionnaire) and in the school setting (teacher questionnaire). In total,30 children (14 males, 16 females), all from the mental health agencies, met thesecriteria. The mean scores for children in the SM group on the SSQ-Parent andSSQ-Teacher were 17.44 (range 5 9–30) and 4.92 (range 5 0–14), respectively. Asindicated by the ranges, the maximum possible values for the parent and teacherSSQ were reached. This was due to two participants whose primary caregiversindicated that their children spoke normally in all situations but whose teachersindicated that they never spoke in two or more situations in the school setting.Similarly, there were seven children whose parents indicated that they failed tospeak in two or more situations, but whose teachers indicated that they spokenormally in the school setting. All of the children in the SM group received atleast one rating from either their primary caregiver or their teacher indicatingthat they never spoke in some aspect of the school setting (i.e. in the classroom totheir friends, in the classroom to the teacher, in front of the class, etc.). The primary caregiver also completed the internalizing section of the Com-puterized Diagnostic Individual Schedule for Children (C-DISC IV; Shaffer,Fisher, Lucas, Dulcan, & Schwab-Stone, 2000) over the phone to assess for co-morbid internalizing disorders. The C-DISC was not available for 2 (6%) of thechildren in the SM group because a time could not be scheduled with the primarycaregiver to complete the C-DISC over the phone. Of the 28 children with SM forCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 26. 276 Table 1. Demographic characteristics for the full sample (N 5 108) Selective mutism Mixed anxiety Community control Statistic p-Value (n 5 30) (n 5 46) (n 5 27) Percent female 53 48 56 w2(2) 5 0.47 p 5 0.79 Mean Age of Child (years) 8.8 (3.5) 9.3 (2.8) 7.8 years (2.4) F(2, 100 ) 5 2.25 p 5 0.11 Percent in regular classroom 97% 100% 100% w2(2) 5 2.39 p 5 0.30 Copyright r 2009 John Wiley & Sons, Ltd. Age range of primary caregiver (years)a 19–39 (n 5 12), 19–39 (n 5 18), 19–39 (n 5 12), w2(4) 5 2.74 p 5 0.60 40–64 (n 5 18) 40–64 (n 5 28) 40–64 (n 5 15) Percent English spoken at home 90 100 100 w2(2) 5 7.78 p 5 0.02 Percent of participants who fall in each w2(2) 5 28.98 p 5 0.004 of the following total income levels Less than $15 000 0 4 0 $15 000–$30 000 7 15 0 $30 000–$45 000 13 9 0 $45 000–$60 000 0 15 0 $60 000–$75 000 37 9 28 $75 000–$90 000 23 20 40 Greater than $100 000 20 28 32 a Differences between sample sizes for groups and the number of responses are due to missing data. M.E. Nowakowski et al.Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 27. Language and Academic Abilities in Children 277which the C-DISC was available, 15 (54%) had one or more comorbid inter-nalizing disorders. The C-DISC was used to determine the diagnoses of anxietydisorders because it has been shown to have good reliability in assessing anxietydisorders (Shaffer et al., 2000). However, the C-DISC has not been used in the pastfor diagnosing SM, and its reliability for this diagnosis has not been established.Accordingly, we used the parent and teacher-report questionnaires to identifychildren with SM and the C-DISC to identify comorbid anxiety disorders. Themean age of the children in the SM group was 8.8 years (S.D. 5 3.46 years). Withthe exception of one child, all of the children with SM were in a regular classroomand followed the regular academic programme. In all but three of the homes,English was the language most commonly spoken (see Table 1).Mixed anxiety group The inclusion criteria for the mixed anxiety group were that the children hadto have one or more anxiety disorder diagnoses on the C-DISC IV (social phobia,separation anxiety, specific phobia, panic disorder, post-traumatic stress disorder,obsessive compulsive disorder, or agoraphobia) and no diagnosis of SM, as de-termined by teacher and parent ratings on the SSQs. Forty-six children (24 males,22 females), 11 (24%) of whom were recruited from the child database, met thesecriteria. The mean scores for the parent and teacher SSQ questionnaire for themixed anxiety group were 26.82 (range 5 8–30) and 12.89 (range 5 5–14), re-spectively. Of the 46 children in the mixed anxiety group, 25 (54%) had oneanxiety disorder while 21 (46%) had two or more anxiety disorder diagnosesaccording to the C-DISC. It should be noted that although we had originallyintended to have a pure social phobia group as our anxiety comparison group,we found that the high comorbidity of anxiety disorders made the attainment ofsuch a group very difficult. Given the wide range of anxiety disorders that wefound in our sample, we decided to create a mixed anxiety group based on thecriteria outlined above. The mean age of the children was 9.28 years (S.D. 5 2.78years). All the children were in a regular classroom and followed the regularclassroom programme. In all the families, English was spoken most commonly inthe home (see Table 1).Community control group The selection criteria for the community control group were that they were: (1)healthy children from the Child Database; (2) had no anxiety disorders as de-termined by the C-DISC IV; and (3), had no diagnosis of SM, as determined byteacher and parent ratings on the SSQ. The mean scores for the parent andteacher SSQ questionnaires were 29.39 (range 5 27–30) and 13.21 (range 5 10–14),respectively. Twenty-seven children (12 males, 15 females) met these criteria. Themean age of the children was 7.8 years (S.D. 5 2.4 years). All the children were ina regular classroom and followed the regular academic programme. In all of thehomes, English was the most common language spoken (see Table 1).ProceduresThis study was part of a larger study investigating the aetiology, familialbackground, academic performance, and behavioural and psychophysiologicalcharacteristics of children with SM. The present paper focused only on theacademic and receptive vocabulary measures that were collected. All proceduresCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 28. 278 M.E. Nowakowski et al.were approved by the McMaster University Health Sciences Research EthicsBoard. All children and primary caregivers were tested at the Child EmotionLaboratory at McMaster University. Upon arrival at the laboratory, the primary caregiver and child were briefedabout the procedures and consent forms were signed. The primary caregiver alsoprovided the name of the child’s current school and grade teacher. All of themeasures in the laboratory were completed in a quiet room with a video camerathat was visible to both the child and primary caregiver/experimenter. With theexception of the Reading Recognition subtest, all the measures were completedwith the experimenter while the primary caregiver was in the other room. Thelaboratory visit took approximately 2 h. In order to decrease the length of thelaboratory visit, the parents were contacted after the visit to complete the C-DISCover the phone. The children received a toy at the end of the study as a token ofour appreciation for their participation. Following the completion of the laboratory visit, a package of questionnaireswas sent to the child’s teacher asking him/her to complete the enclosed ques-tionnaires within a week of receiving them and to send them back to the la-boratory in the included self-addressed envelope. The teachers were notcompensated for their participation.Parent and Teacher MeasuresDiagnostic questionnaires completed by primary caregiverThe primary caregiver completed the SSQ-Parent (Cunningham et al., 2004;Cunningham et al., 2006) as a measure of the child’s speaking patterns. TheSSQ-Parent is a 15-item questionnaire in which parents rate their children’sspeaking in a variety of situations, including the home, school, and community,and to a range of different people, including parents, friends, teachers, andstrangers on a 3-point scale (0 5 never talks, 1 5 whispers, 2 5 talks in a normalvoice). For the purpose of diagnosing children with SM, the primary caregiverhad to select never talks (i.e. 0) for a minimum of two situations. The internalconsistency of the SSQ—Parent Version in a past study was 0.82 (Cunninghamet al., 2006) and in the present study was 0.92. The primary caregiver also completed the internalizing disorders portion ofthe C-DISC IV (Shaffer et al., 2000). The C-DISC IV is a structured diagnosticinterview based on the DSM-IV that assesses children for 34 psychiatric dis-orders. It has been shown to have good reliability (Shaffer et al., 2000). The C-DISC IV was administered to the primary caregiver over the phone by a trainedresearch assistant after the laboratory visit. To decrease the amount of time theassessment took and due to the fact that the present study was focused on in-ternalizing disorders, only the internalizing disorders section of the C-DISC IVwas administered. The children were assessed for the following internalizingdisorders: panic disorder, generalized anxiety disorder, social phobia, specificphobia, separation anxiety, obsessive compulsive disorder, post-traumatic stressdisorder, agoraphobia, and major depression.Diagnostic questionnaires completed by teachers The teachers completed the SSQ-Teacher to evaluate student’s speech patternsin the school setting. The SSQ-Teacher is a 7-item questionnaire in which teachersassess children’s speech in a variety of school settings, such as the playground,the hallway and the classroom, and to a variety of individuals, including friendsCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 29. Language and Academic Abilities in Children 279and teachers, on a 3-point scale (0 5 never talks, 1 5 whispers, 2 5 talks in normalvoice). For the purpose of diagnosing children with SM, the teacher had to selectnever talks (i.e. 0) for a minimum of two situations. The internal consistency ofthe SSQ-Teacher in the present study was 0.95.Child Academic Skill and Receptive Vocabulary MeasuresPPVT-IIIThe receptive vocabulary of the child was measured through the Peabody PictureVocabulary Test—3rd Edition (PPVT-III; Dunn & Dunn, 1997), which comprises204 words sequenced to be increasingly challenging. The experimenter says atarget word and the child is presented with four line drawings and has toindicate which one of the line drawings corresponds to the word. The PPVT-IIIwas introduced to the children as a picture game. The PPVT-III raw scores wereconverted to standard age-normed scores. The internal consistency of the PPVT-III has been estimated at 0.90 (Dunn & Dunn, 1997).PIAT-R The Reading Recognition, Mathematics, and Spelling subtests of the Peabody In-dividual Achievement Test—Revised (PIAT-R; Dunn & Markwardt, 1998) were con-ducted as standardized measures of children’s oral reading, mathematics, and spellingabilities. These subtests were completed only by children who were 5 years old orolder, given that the youngest age for which the assessment is standardized is 5 years.The internal consistency of the subtests of the PIAT-R ranges from the low to mid 0.90 s.All the assessments from thePIAT-R were videotaped. The Reading Recognition subtest comprises 100 words that are arranged inorder of difficulty. The child is presented with 12 words on a page and is asked toread them out loud to the tester. Unlike the other subtests, given that this taskrequires verbal responses the children completed it with their primary caregiverwhile the experimenter was out of sight. The primary caregiver was instructed bythe experimenter while the child was in an adjoining room to read the providedinstructions to the child asking the child to read the presented words from left toright. The primary caregiver was told to indicate on the provided form whetherthe child read the word correctly but to not let the child know his/her accuracy.Testing was complete when the child made five mistakes on seven consecutivewords. The experimenter entered the room with the primary caregiver to set upthe materials for the reading recognition subtest and told the child that he/shewould be doing a word game with his/her parent and then left the room. The Mathematics subtest comprises 100 math questions that are arranged inorder of difficulty. The experimenter reads a math question to the child, and thechild is presented with four numbered options, one of which is the correct answerand three that are distracters. The PIAT-R-M was introduced to the children as anumber game. The children indicated their answers by either saying the numberthat corresponded to the correct answer or pointing to the correct answer. The Spelling subtest comprises 100 words that are arranged in order of diffi-culty. The experimenter reads a target word, reads a sentence that contains thetarget word, and then reads the target word again. The child is presented withfour numbered options, one of which is the target word spelled correctly andthree of which are distracters. The subtest was introduced to the children as aword game. The children indicated the correct answer either by saying thenumber that corresponded to the correct answer or pointing to the correct answer.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 30. 280 M.E. Nowakowski et al.Data LossThere was some variability in the number of participants who completed thestandardized tests due perhaps to fatigue or anxiety in the children, or a lack ofavailability of the testing materials. Of the 26 children with SM who were 5 yearsold or older and were eligible to complete all subtests of the PIAT-R, 7 (27%)failed to complete the Reading Recognition subtest, 1 (4%) failed to complete theMathematics subtest, and 1 (4%) failed to complete the Spelling subtest. Of the 30children with SM, 5 (17%) failed to complete the PPVT-III (4 of these were due toan initial lack of availability of testing materials). Of the 44 mixed anxietychildren who were 5 years old or older and eligible to complete all subtests of thePIAT-R, 3 (7%) failed to complete the Reading Recognition subtest. Of the full 46children in the mixed anxiety group, 3 (6%) failed to complete PPVT-III (2 ofthese were due to a lack of available testing materials). Of the 23 children in thecommunity control group who were 5 years old or older and eligible to completeall subtests of the PIAT-R, 1 (4%) failed to complete the Reading Recognitionsubtest. All the children in the community control group completed the PPVT-III.RESULTSPreliminary AnalysesThere was a statistically significant difference on language spoken at home(w2(2) 5 7.78, p 5 0.02; see Table 1). All the children in the community control andmixed anxiety groups spoke English most frequently at home while 3 of the 30children with SM spoke a different language at home. However, when weeliminated the three children with SM who spoke a different language at home,the differences between the groups for the standardized tests of academicperformance were still statistically significant. Therefore, we included the threechildren with SM who spoke a different language at home in the analysespresented here. There were no significant correlations between the standardizedscores for the academic measures (PPVT-III, reading recognition, mathematics,and spelling subtests of the PIAT-R) and income levels. Therefore, we did notconsider the differences in income levels as confounding factors in our analyses.Academic Standardized MeasuresMeans and standard deviations for all the dependent variables are shown inTable 2.Table 2. Means and standard deviations for the PPVT-III standardized scores amongmales and females in the three groupsPPVT-III Male Female Selective Mixed Control Selective Mixed Control mutism anxiety (n 5 12) mutism anxiety (n 5 14) (n 5 12) (n 5 24) M (S.D.) (n 5 13) (n 5 19) M (S.D.) M (S.D.) M (S.D.) M (S.D.) M (S.D.) 102.67 108.83 108.58 105.92 102.53 116.07 (12.87) (11.27) (14.00) (9.27) (13.76) (9.02)Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 31. Language and Academic Abilities in Children 281Figure 1. Standardized scores for the Peabody Picture Vocabulary Test—3rd Edition forthe selective mutism (n 5 30), mixed anxiety (n 5 46), and community control (n 5 27)groups among females and males. The error bars are 95% confidence intervals.PPVT-III To examine receptive vocabulary differences among the three groups and thesexes, a 3 Â 2 analyses of variance (ANOVA) was conducted with Group (SM,Mixed Anxiety, and Community Control) and sex (male and female) as the in-dependent variables and PPVT-III standard score as the dependent measure.There was a significant main effect for group (F(2, 88) 5 3.51, p 5 0.03, Z2 ¼ 0:074) pas well as a significant group by sex interaction on the standard score of thePPVT-III (F(2, 88) 5 3.02, p 5 0.05, Z2 ¼ 0:064; see Figure 1). Given the significant pinteraction, we conducted simple main effects to decompose the interaction(using LSD tests to compare relevant means). Results indicated that for girls, boththe SM (n 5 13; M 5 105.92, S.D. 5 9.27) and the mixed anxiety (n 5 19;M 5 102.53, S.D. 5 13.76) groups attained significantly lower standardized scoreson the PPVT-III compared with the control group (n 5 14; M 5 116.07, S.D. 5 9.02,p 5 0.03 and 0.002, respectively). In contrast, for boys there were no significantdifferences between the SM (n 5 12; M 5 102.67, S.D. 5 12.87) and mixed anxiety(n 5 24; M 5 108.83, S.D. 5 11.27; p 5 0.15) groups, the SM and control groups(n 5 24; M 5 108.58, S.D. 5 14.00; p 5 0.23), or the mixed anxiety and controlgroups (p 5 0.95). We also conducted w2 tests to look at differences between groups within eachsex in the frequency of children in each group who scored at or below the 25thpercentile or at or above the 75th percentile on the PPVT-III. Among girls, therewas a significant difference between groups with only 5 out of 13 (i.e. 38%) girlsfrom the SM group and 5 out of 19 (i.e. 26%) of girls from the mixed anxietygroup scoring at or above the 75th percentile, whereas 12 out of 14 (i.e. 86%) girlsCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 32. 282 M.E. Nowakowski et al.from the community control group scored at or above the 75th percentile(w2(2) 5 12.03, p 5 0.002). We found no significant differences between groups inthe number of girls who scored at or below the 25th percentile on the PPVT-III(w2(2) 5 2.55, p 5 0.28). For boys, we found no significant differences betweengroups in the number of children who scored at or below the 25th percentile(w2(2) 5 0.67, p 5 0.72) or at or above the 75th percentile (w2(2) 5 0.17, p 5 0.92) onthe PPVT-III.PIAT-R To examine differences between groups and sexes on the standardized scoresfor the PIAT-R subtests, a two-way multivariate analysis of variance (MANOVA)was conducted with Group (SM, Mixed Anxiety, Community Control) and Sex(male and female) as the independent variables and the three PIAT-R subtests(reading recognition, math, and spelling) as the dependent variables. TheMANOVA failed to yield a significant group by sex interaction, but did yield astatistically significant main effect of group, which was followed up with AN-OVA on the dependent variables. All significant ANOVAs were further followedup using post hoc Tukey HSD tests given that the equal variances assumptionwas met. There was a significant main effect for group on the PIAT-R (F(6, 152) 5 3.58,p 5 0.002, Z2 ¼ 0:13). The follow-up one-way ANOVAs on the dependent mea- psures showed that the groups differed significantly only on the math subtest ofthe PIAT-R (F(2, 77) 5 6.39, p 5 0.003, Z2 ¼ 0:14; see Figure 2). Both the SM p(M 5 96.00, S.D. 5 14.08) and mixed anxiety groups (M 5 100.45, S.D. 5 12.45) hadsignificantly lower mathematics scores than the community control groupFigure 2. Standardized scores for the Mathematics Assessment of the Peabody IndividualAssessment Test—Revised for the selective mutism (n 5 30), mixed anxiety (n 5 46), andcommunity control (n 5 27) groups. The error bars are 95% confidence intervals.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 33. Language and Academic Abilities in Children 283Table 3. Means and standard deviations for all three groups for the reading, math, andspelling subtests of the PIAT-RPIAT-R Selective mutism Mixed anxiety Community control (n 5 30) (n 5 46) (n 5 27) M S.D. M S.D. M S.D.Reading Recognitiona 112.26 20.13 106.93 12.17 109.64 13.08Matha 96 14.08 100.45 12.45 110.86 14.83Spellinga 103 14.35 104.48 13.89 106.27 12.49a Analyses completed on the following sample sizes due to missing data: Selective mutism (n 5 19), Mixed Anxiety (n 5 42), Control (n 5 22).(M 5 110.86, S.D. 5 14.83) (Table 3). There were no significant differences betweenthe SM and the mixed anxiety groups (p 5 0.47). There were no significant dif-ferences between the groups on the spelling (SM and mixed anxiety, p 5 0.92; SMand control, p 5 0.73; mixed anxiety and control, p 5 0.88) and reading recogni-tion subtests of the PIAT-R (SM and mixed anxiety, p 5 0.40; SM and control,p 5 0.84; mixed anxiety and control, p 5 0.77). Using w2 tests, we also found a significant difference between groups in thenumber of participants who scored at or above the 75th percentile on themathematics subtest of the PIAT-R (w2(2) 5 12.71, p 5 0.002). Only 1 child (i.e. 4%)from the SM group and 10 (i.e. 23%) children from the mixed anxiety groupscored at or above the 75th percentile on the math subtest of the PIAT-R, while 11children (i.e. 48%) from the community control group scored at or above the 75thpercentile on the math subtest of the PIAT-R. There were no significant differencesin the number of participants who scored at or below the 25th percentile on themath subtest of the PIAT-R (w2(2) 5 2.08, p 5 0.35). There were no other differencesbetween groups in the distribution of scores for the subtests of the PIAT-R.DISCUSSIONThe goal of this study was to explore the language abilities of children with SM.We found that girls with SM and mixed anxiety performed significantly lower ontests of receptive vocabulary skills as compared with community controls, butthere were no significant differences between groups for boys. We also found thatchildren with SM and mixed anxiety scored significantly lower than communitycontrols on tests of mathematics skills (regardless of sex). There were nosignificant differences between children with SM and children with mixedanxiety on any of the other standardized measures. However, despite thestatistically significant differences, the average receptive vocabulary standar-dized scores for girls with SM and mixed anxiety were age-appropriatecompared with normative data (i.e. 106 and 102). Similarly, the standardizedscores for the mathematics for children with SM and children with mixed anxietywere average or age-appropriate compared with normative data (i.e. 96 and 100,respectively). Similar results were found when looking at the percentage of children scoring at orbelow the 25th percentile and at or above the 75th percentile for receptive vocabularyand mathematics performance. That is, fewer individuals with SM and mixed scoresCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 34. 284 M.E. Nowakowski et al.at or above the 75th percentile on the standardized tests of mathematics and receptivevocabulary (girls only) compared with the community controls.Language SkillsIn terms of receptive language, it may appear that girls with SM and mixedanxiety are neither significantly impaired nor significantly advanced in theirreceptive vocabulary abilities, whereas comparison girls were above average inthese abilities. However, research has also shown that receptive vocabularyabilities as measured by the PPVT-III tend to be inflated, resulting in childrenwith receptive language difficulties often not being identified as clinicallyimpaired (Ukrainetz & Duncan, 2000). For example, William (1998) reported thatchildren obtained standardized scores that were about 10 points higher on thePPVT-III than on the PPVT-R (Dunn & Dunn, 1981). Moreover, this score inflationwas especially evident in children between the ages of 4 and 10 (the age of focusfor the present study). Therefore, it may be the case that the children with SM arein fact performing below their age-appropriate norms but this is not beingrevealed through the standardized scores on the PPVT-III. Notwithstanding the group by sex interaction, there was a significant maineffect for group on receptive vocabulary ability with children with SM scoringsignificantly lower (but within the age-appropriate range) than communitycontrols. This is consistent with previous studies that have found lower scores onthe PPVT-III in children with SM (Kristensen & Oerbeck, 2006; Manassis et al.,2007; McInnes et al., 2004). Unlike these previous studies, however, we did notfind any significant differences between the SM and the mixed anxiety groups inreceptive vocabulary scores. One possible explanation for this discrepancy in results is that in the studyconducted by McInnes et al., (2004), the SM group had children who had only adiagnosis of SM and the social phobia group comprised children who had only adiagnosis of social phobia. In contrast, over half of the children in our SM grouphad one or more comorbid anxiety disorders and our mixed anxiety groupconsisted of a number of different anxiety disorders. In addition, even though thestudy conducted by Manassis et al., (2007) included children with SM who had acomorbid anxiety disorder, the majority of these children had comorbid socialphobia. In contrast, in our study there was a wide variety of comorbid disordersfor children with SM, with the most common being specific phobia. As well,differences in age between the SM group and the anxiety group in previousstudies (e.g. Manassis et al., 2007) may have also influenced results. 1 The main effects we noted for group on receptive vocabulary are also con-sistent with previous work investigating the expressive and receptive languageabilities of temperamentally shy children (Rubin, 1982; Spere, Schmidt, Theall-Honey, & Martin-Chang, 2004). Moreover, these findings also provide furtherevidence for the similarities that have been highlighted by a number of re-searchers (Black & Uhde, 1995; Dummit et al., 1997) between children with SMand Kagan’s (1987) conceptualization of the behaviourally inhibited child. Like previous studies, we also found that children with SM performed sig-nificantly lower than controls on receptive vocabulary tests. Based on standar-dized scores, these differences did not reflect serious receptive vocabularydeficits (e.g. Spere et al., 2004), although, as discussed above, this may be areflection of the score inflation that is seen in the PPVT-III. Our study, however,suggests that the picture is more complex as we also found a significant group bysex interaction, whereby only girls with SM and females with mixed anxietyCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 35. Language and Academic Abilities in Children 285performed significantly lower than community control on receptive vocabulary.Again, however, this significant difference did not place the females with SM ormixed anxiety as having a deficit in receptive vocabulary abilities based onstandardized scores but rather reflected the fact that the community control girlswere high average on receptive vocabulary performance. This finding is con-sistent with research that has shown that girls tend to be more advanced thansame-aged boys in their language development, especially with regards to vo-cabulary (Bornstein, Hahn, & Haynes, 2004). One mechanism that has beensuggested for this advanced language ability in females is that the activities thatare stereotyped as being female and that young girls are likely to engage inpromote collaboration and proximity to others (Caldera, Huston, & O’Brien,1989). Consequently, girls who do not engage in such activities are unlikely toattain the advanced language abilities, helping to explain why only the girls inthe SM and mixed anxiety groups scored significantly lower on receptive voca-bulary compared with females in the community control group.Mathematic SkillsWith regards to mathematics, the only other study that we are aware of that hasspecifically investigated mathematics skills in children with SM was conductedby Cunningham et al., (2004), who found no significant differences inmathematics abilities between children with SM and community controls. Thereare two possible explanations for the discrepancies in findings on mathematicsabilities between the present study and the study conducted by Cunninghamet al., (2004). First, the children with SM in the study conducted by Cunninghamet al., (2004) had a mean age of 7.1 years, and thus were younger than the childrenwith SM in our study, who had a mean age of 8.8 years. It is possible that thedifferences that are observed between children with SM and community controlson mathematics standardized scores are not seen early in the child’s educationbut manifest themselves as the children get older and academic demands inmathematics increase. 2 Second, in the study conducted by Cunningham et al., (2004), the standardizedmath scores for both groups of children were actually lower than the scores in thepresent study. The difference was that the standardized math scores for thecommunity controls in the Cunningham et al., (2004) study were substantiallylower than those of the community control group in the current study. A possibleexplanation for the differences in these standardized scores is that Cunninghamet al., (2004) used a more sophisticated sampling strategy to compose the com-munity control group and had a higher participation rate. The tendency for fewer children with SM to score above their age levels formathematics may be a reflection of their lack of speaking in school situations.Research has shown that children who explain and discuss new concepts withtheir classmates, enhance their learning (Nattive, 1994). Thus, is likely that chil-dren elaborate and solidify their learning of mathematical concepts by discussingthe concepts with their classmates. However, children with SM typically will notengage in such discussions. Consequently, these children may lack the solidifi-cation of concepts that occurs through discussion. Furthermore, children with SMmay be less likely to ask teachers questions when they do not understandsomething. Given that mathematics concepts tend to build upon each other,children with SM may experience more difficulties with mathematics due to theirlack of ability to ask for help when needed.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 36. 286 M.E. Nowakowski et al.Spelling and Reading SkillsThere were no significant differences between children with SM and communitycontrols on spelling and reading abilities. This result suggests that children withSM have specific academic areas where they may score lower than communitycontrols (i.e. math and receptive vocabulary). It is possible that parentalinvolvement is reflected in the results. Parents view the school as primarilyresponsible for the teaching of mathematics but often see the home as playing akey role in the development of literacy skills (Evans, Fox, Creamos, & McKinnon,2004). Parents of children with SM may take a particularly active approach indeveloping their children’s reading abilities given that their children fail toparticipate verbally in the school setting, and work with their children at home toteach them to read. These parental interventions in the home setting wherechildren with SM are most comfortable may help to ensure that they learn to readat the same level as their peers. Given that little past research has looked atspelling and reading abilities in children with SM, these results need furtherreplication to fully understand their meaning and implications.Strengths and LimitationsThe current study had a number of strengths. First, it appears to be the first studyto examine all aspects of academic performance in one sample of children withSM. Second, we used methods to evaluate children’s academic abilities that didnot rely on verbal responses. With the exception of the reading assessment, whichwas done with the primary caregiver, the nature of all the assessment was suchthat they could be completed by the child either verbally or non-verbally. Thus,the lack of speaking found in children with SM was not a confounding factor inevaluating their academic abilities. Third, given the rarity of SM, obtainingsample sizes large enough to confidently assess differences between groups is achallenge. The current study had a relatively large group of children with SM,thus enabling the statistical power required for valid comparisons betweengroups. Despite the aforementioned strengths, the current study also has a number oflimitations. Although, as mentioned above, our sample was quite large con-sidering the rarity of the disorder, our investigation of group by sex interactionsfor academic performance resulted in comparisons of fairly small sample sizes.Future studies with larger samples are necessary to replicate our results. Further,given that SM is highly comorbid with other anxiety disorders, we were not ableto have a pure SM group. Therefore, it is possible that we did not observe dif-ferences between the SM and mixed anxiety groups because over half of thechildren in the SM group also had an anxiety disorder. As well, due to the highrate of comorbidity, we cannot determine whether the difference between the SMgroup and the community controls is due to the speaking inhibition of thechildren with SM or due to their anxiety levels. 3 The results need to be replicatedwith a larger and more pure sample to fully delineate the effect of SM as opposedto anxiety per se on receptive vocabulary ability and academic performance inreading, mathematics, and spelling. Second, although the children with SM were not required to provide verbalresponses for the academic tasks, the presence of the experimenter may haveresulted in high levels of anxiety and inhibition in the children. Thus, the groupdifferences found for mathematics and receptive vocabulary abilities couldpossibly be a reflection of general inhibition rather than a lack of ability orCopyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 37. Language and Academic Abilities in Children 287knowledge (although it is not clear why this would affect just mathematics andreceptive vocabulary). Third, again due to the high comorbidity of different anxiety disorders, ourmixed anxiety group was a combination of different types of anxiety disorders.There was also differing levels of impairment in the mixed anxiety group (e.g.single vs multiple anxiety disorders). Fourth, the inclusion criteria for our com-munity control group were very strict, given that the children not only had tohave no diagnoses on the C-DISC, but they also had to be recruited from the childdatabase. This may have limited the generalizability of our results in two ways:(a) it is possible that the differences that we saw between the children with SMand the community controls were not due to SM but rather due to a self-selectionbias whereby children from mental health agencies may have lower academicscores, in addition to other difficulties, compared with community controls; (b) itis possible that the strict inclusion criteria for the community controls resulted inthe community controls being selected from a non-representative population thathad high average academic scores, given that our community controls hadsubstantially higher standardized mathematics scores than the community con-trols in the study conducted by Cunningham et al., (2004). Fifth, the groups differed significantly in their income levels with the com-munity control group having significantly higher incomes than the SM andmixed anxiety groups. Even though we did not find any significant correlationsbetween income level and academic performance in our data, it is still possiblethat income level may have influenced the results given that families who havehigher income levels may have more resources to put towards the educationaldevelopment of their children. Sixth, we used only one measure of receptive language ability: the PPVT-III.This test has been shown to produce inflated standardized scores, resulting inchildren with vocabulary difficulties being missed or misidentified as being lowaverage but within age-appropriate norms. Therefore, our lack of clinical sig-nificance between the girls with SM and community controls has two possibleinterpretations: (1) it may be a true lack of clinical significance; and (2) it may be areflection of score inflation. Future studies should look at more than one stan-dardized receptive language measure to delineate the clinically significant dif-ferences between the groups on receptive vocabulary performance. Finally, given that both the parent and teacher versions of the SSQ have onlybeen used in two other studies to date, there is no test–retest reliability data on thequestionnaire, as they have not been utilized in any longitudinal studies. This is alimitation of the study as we relied on the questionnaire for our group classification. Our results suggest that, despite their lack of speaking in the school setting,children with SM are still able to acquire the necessary academic knowledge toachieve average performance for their ages, with regards to reading, mathe-matics, and spelling. Given that we found no significant differences betweenchildren with SM and children with mixed anxiety, and that our results forreceptive vocabulary abilities resemble those of children with temperamentalshyness, our study provides further support for the idea that SM can be con-ceptualized as sharing commonalities with behaviourally inhibited children.Future studies should take a longitudinal approach to investigate how thesechildren’s academic abilities develop over time and whether they continue toattain the academic levels expected for their age as they get older. Further, lan-guage assessment using more than one standardized test would be helpful infurther delineating the meaning of the lack of receptive language deficits asmeasured through the PPVT-III.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
  • 38. 288 M.E. Nowakowski et al.Notes1. We did conduct an exploratory analysis comparing children with SM only and children with SM who also had comorbid anxiety disorders on the academic measures. The only significant difference for the math subtest of the PIAT-R (t(21) 5 À2.21, p 5 0.04), where children with SM only (M 5 93.33, S.D. 5 8.57) performed significantly lower than children with SM and comorbid anxiety (M 5 110.55, S.D. 5 9.08). This finding was somewhat puzzling as one would expect that comorbidity would lead to greater functional impairment. However, the analyses were performed on a very small sample (n 5 9 for SM only, n 5 14 for SM and anxiety). Thus, a future study with a larger sample size is necessary to further analyze and interpret the differences between children with SM only and children with selective mutsim and comorbid anxiety.2. To further evaluate this hypothesis, we correlated math scores with children’s age for the SM group and found a significant negative correlation between age and standardized score on the math subtest of the PIAT-R (r(43) 5 À0.44, po0.001). There were no significant correlations between age and math standardized score for the mixed anxiety or community control groups. This provides at least some preliminary evidence that the mathematics perfor- mance of children with SM may decrease as children get older. A longitudinal study looking at the mathematics performance of children with SM would be helpful in further understanding this relation.3. Although we did attempt to parse the children into those who presented only with SM and those who presented with SM and comorbid anxiety, the sample sizes for our comparisons were small, thus not allowing us to make any strong conclusions about the implications of comorbid anxiety disorders in the academic performance of children with SM.ACKNOWLEDGEMENTSThis research was supported by a grant from the Ontario Mental HealthFoundation (OMHF). The authors would like to thank Lindsay Bennett, SueMcKee, Renee Nossal, and Jamie Sawyer for their assistance with data collectionand coding. We would also like to thank many children their parents andteachers for their participation in the study.REFERENCESAmerican Psychiatric Association. (1994). Diagnsotic and statistical manual of mental disorders (4th ed.). Washington, DC: American Psychiatric Association.Anstendig, K. D. (1999). Is selective mutism and anxiety disorder? Rethinking its DSM-IV classification. Journal of Anxiety Disorder, 13, 417–434.Bergman, L. R., Piacentini, J., & McCracken, J. T. (2002). Prevalence and description of selective mutism in a school-based sample. Journal of the American Academy of Child and Adolescent Psychiatry, 41, 938–946.Black, B., & Uhde, T. W. (1995). Psychiatric characteristics of children with selective mutism: A pilot study. Journal of the American Academy of Child and Adolescent Psychiatry, 34, 847–856.Bornstein, M. H., Hahn, C., & Haynes, M. O. (2004). Specific and general language performance across early childhood: Stability and gender considerations. First Language, 24, 267–304.Copyright r 2009 John Wiley & Sons, Ltd. Inf. Child. Dev. 18: 271–290 (2009) DOI: 10.1002/icd
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