Information collected in a quantified (numeric ) form.
Quantitative Research :
The investigation of phenomena that lend themselves to precise measurement and quantification, often involving a rigorous and controlled design.
Quantitative Analysis:
Manipulation of numeric data through statistical procedures for the purpose of describing phenomena or assessing the magnitude and reliability of relationships among them.
If the directions for obtaining measures are poorly understood, then scores may be affected by misunderstanding. E.g. Self - report instrument may be interpreted differently by different respondents.
6. Item Sampling:
Errors can be introduced as a result of the sampling of items used in the measure.
7. Instrument format: Technical characteristics of an instrument. E.g open ended questions yield different information than closed ones.
The stability of an instrument is the extent to which similar results are obtained on two separate occasions.
Assessments of an instrument’s stability involve procedures that evaluate test – retest reliability.
e.g. Administer the same measure to a sample twice and then compare the scores by computing a reliability coefficient, which is an index of the magnitude of the test’s reliability. Statistical analysis is correlation –coefficient.
Refers to whether the instrument looks as though it is measuring the appropriate.
Scale is established by consulting the experts and person with a same disease
2. Content Validity:
Concerns the degree to which an instrument has an appropriate sample of items for the construct being measured and adequately covers the construct domain.
Content validity is relevant for both affective and cognitive measures
Calculate the Content Validity index,(CVI) Experts rate items on a 4 – point scale of relevance, the item(I) CVI is computed as the number of raters giving a rating of either 3 or 4 , divided by the number of experts.I-CVI of .80 is considered an acceptable value.
Concurrent Validity refers to a measurement device’s ability to vary directly with a measure of the same construct or indirectly with a measure of an opposite construct. It allows you to show that your test is valid by comparing it with an already valid test.
Determines the relationship between an instrument and an external criterion.
The instrument is said to be valid if its scores correlate highly with scores on the criterion.
Two types of criterion related validity:
a) Predictive validity : Refers to the adequacy of an instrument in differentiating between people’s performance on some future criterion. e.g , High school grades for nursing school performance
An important construct validation tool is a procedure known as the Multitrait – multimethod matrix method which involves convergence and Discriminiability.
Convergence is evidence that different methods of measuring a construct yield similar results.e.g Self report,Observation etc.
Discriminiability is the ability to differentiate the construct from other similar constructs.
Criteria for screening and diagnostic instruments:
Sensitivity and Specificity
Sensitivity is the instrument’s ability to identify a case correctly.(Its rate of yielding true positives)
True positives divided by positives, (Smokers who had high cotinine / all real smokers)
Specificity is the instrument’s ability to identify non cases correctly.(Its rate of yielding true negatives)Teenagers reported that they did not smoke,True negatives / all negatives.
28.
Urinary cotininie level Sensitivity = A/(A+C) = .50, Specificity = D/ (B+D) = .83 ( Percentage) Positive predictive value = A/(A+B) =.67 Negative predictive value =D/(C=D)=.71 Likelihood ratio –Positive (LR+) = Sensitivity/(1- Specificity) = 2.99 Likelihood ratio – Negative(LR_) = (1- sensitivity) / specificity =.60 LR Summarizes the relationship specificity and sensitivity in a single number. Self Reported smoking Positive Cotinine Negative Cotinine Total Yes , Smoked A (True positive) 20 B (False positive)10 A+B =30 No,Did not smoke C (False negative)20 D(True negative)50 C+D = 70 A+C=40 B+D=60 A+B+C+D 100
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