The Subject-Experimenter Contract: A Reexamination of Subject Pool Contamination Kitty Klein Brian Cheuvront North Carolina State University W e conducted three experiments to investigate: ( a ) the extent to which student research participants believe they will disclose de- tuils of their experiences, ( b ) how much subjects uctually will disclose immediately following a request not to reveal i n f o m - tion, and ( c ) how much they will disclose after a 2-week interval. Disclosure rates increused across the experiments. In the first experiment, one fifth of the subjects indicated that they probably would not preserve confidentiality, whether or not they believed it was important to do so. In the second experiment, signing a pledge not to discuss the experiment resulted in less disclosure, but over one third o f the subjects revealed information to a confederate. In the third experiment, promising students anonymity increased disclosure; 85% of the subjects disclosed information, The results indicate thut failure to heed requests for confidentiality may be ( 1 widespread problem in college subject pools. In recent years, we have seen a renewed concern that undergraduate students enjoy an ethical and educational experience when they participate in psychological experi- ments. Britton (1987) expressed concern that the direct educational benefits of serving as a research participant are sufficient t o justify the costs to the individuals involved. Kimble (1987) and Korn (1988) outlined the educational benefits students should expect. They emphasized that re- search participants have a right to a discussion of the topic of interest, a n explanation of the procedures followed, and a summary of the results. Nonetheless, Coulter (1986) re- ported that a substantial number of her undergraduates con- sidered their research participation as "boring, irrelevant, and a waste of time" (p. 3 17). She urged experimenters to prepare debriefings that will educate, rather than simply dismiss, student subjects. Another side of this ethical coin has received little discus- sion. With the exception of Korn's (1988) list of participant responsibilities, the rights of the experimenter are rarely addressed. O n e of these rights, the participant's responsihil- ~ t y to honor the researcher's request not to discuss the study with anyone else who might be a participant, was the impe- tus for our article. T h e problem is essentially one of subject pool contamination. Revealing information about a n ex- perimental procedure or outcome may affect the willingness of other students to volunteer for a particular experiment and may alter their behavior if they do participate. As Mar- ans (1988) noted, leaked information has the potential to threaten the internal validity of our results. Subject pool contamination has received some empirical attention, alheit very little. Evidence appears mixed on the se.

1. The Subject-Experimenter Contract: A Reexamination of
Subject Pool Contamination
Kitty Klein
Brian Cheuvront
North Carolina State University
W e conducted three experiments to investigate: ( a ) the
extent to
which student research participants believe they will disclose
de-
tuils of their experiences, ( b ) how much subjects uctually will
disclose immediately following a request not to reveal i n f o m
-
tion, and ( c ) how much they will disclose after a 2-week
interval.
Disclosure rates increused across the experiments. In the first
experiment, one fifth of the subjects indicated that they
probably
would not preserve confidentiality, whether or not they believed
it
was important to do so. In the second experiment, signing a
pledge
not to discuss the experiment resulted in less disclosure, but
over
one third o f the subjects revealed information to a confederate.
In
the third experiment, promising students anonymity increased
disclosure; 85% of the subjects disclosed information, The
results
indicate thut failure to heed requests for confidentiality may be
( 1

2. widespread problem in college subject pools.
In recent years, we have seen a renewed concern that
undergraduate students enjoy an ethical and educational
experience when they participate in psychological experi-
ments. Britton (1987) expressed concern that the direct
educational benefits of serving as a research participant are
sufficient t o justify the costs to the individuals involved.
Kimble (1987) and Korn (1988) outlined the educational
benefits students should expect. They emphasized that re-
search participants have a right to a discussion of the topic of
interest, a n explanation of the procedures followed, and a
summary of the results. Nonetheless, Coulter (1986) re-
ported that a substantial number of her undergraduates con-
sidered their research participation as "boring, irrelevant,
and a waste of time" (p. 3 17). She urged experimenters to
prepare debriefings that will educate, rather than simply
dismiss, student subjects.
Another side of this ethical coin has received little discus-
sion. With the exception of Korn's (1988) list of participant
responsibilities, the rights of the experimenter are rarely
addressed. O n e of these rights, the participant's responsihil-
~ t y to honor the researcher's request not to discuss the study
with anyone else who might be a participant, was the impe-
tus for our article. T h e problem is essentially one of subject
pool contamination. Revealing information about a n ex-
perimental procedure or outcome may affect the willingness
of other students to volunteer for a particular experiment
and may alter their behavior if they do participate. As Mar-
ans (1988) noted, leaked information has the potential to
threaten the internal validity of our results.
Subject pool contamination has received some empirical
attention, alheit very little. Evidence appears mixed on the

3. severity of t h e problem. After using a deception procedure,
Aronson (1966) employed an extensive debriefing that de-
scribed how a n experimental participant who is aware of the
hypothesis could lead researchers to publish erroneous re-
sults. All nine of his subjects admitted to a confederate that
they had participated in the study, but none revealed its true
nature. Two subjects provided a false cover story.
Diener, Matthews, and Smith (1972) also reported low
rates of subject pool contamination. They found that, in ;I
class of 440 nonsubjects, only 11 had knowledge o i a decep-
tive experiment in which 52 of their classmates had
participated.
Other researchers have reported alarming rates of dis-
closure. Wuebben's (1967) subjects participated in a persu;l-
sion experiment in which fear of an unknown disease was
induced. A debriefing, which explained the importance ot
not discussing their participation, was given to the subjects
after t h e first e x ~ e r i m e n t a l session. All subiects were
asked
to nod their head to indicate that they would c o m ~ l v with - ,
the researcher's request not to talk to anyone regarding the
details of the experlment. W h e n they returned for the sec -
ond part of the experlment 1 week later, subjects were ques-
t ~ o n e d about therr compl~ance w ~ t h the expenmenter's
re-
quest. S~xty-four percent a d m ~ t t e d talking to ,it least one
other person about the experlment
Student subjects appear willing to admit that they possess
prior knowledge. In a study using the Taffel verbal condi-
tioning procedure, Farrow, Lohss, Farrow, and Taub ( 1975)
reported that 24% of their subjects acknowledged h a v u n ~
prior information about the experiment.

4. Lichtenstein (1970) also tound high rates o f contamina-
tion in a study that directly measured disclosure, as opposed
to relying o n self-reports. When subjects were ,jpproached
by a confederate identified as a future subiect, no one dis-
closed rnformatlon. W h e n the confederate was ~ d e n t ~ f i
e d ,I.
a nonsubject, 210/0 d~sclosed ~ n f o r m a t ~ o n . After ,In
lntercnl
from 1 dav to 2 weeks. 79% d~sclosed ~nform,itlon to C tele
phone ~nterv~ewer's request for ~ n f o r m , ~ t ~ o n .
G w e n the e v ~ d e n c e that subject pool contamlndtlon oc
curs, one must ask whether sublects' behav~or 1s affected h
prlor knowledge of the procedures, p,lrttcularl when decep-
tlon 1s not a n ~ssue. Levv (1967) > t u d ~ e d the effects of
prlor
awareness o n performance In a Tdftel verbal c o n d l t ~ o n l
n ~
task. Subjects glven full cl~sclosure 11) ,I contederate jur
before partlclpatlon performed better th,in thaw not In
formed, hut speed of l e a r n ~ n g nns nor ,~ffecteJ
Hork'i and Farrow ( 1 970) % t u d ~ e d the hell,~cIor of
elelnen
'Teaching of Psychology
tary school children who could win 5 0 ~ for responding cor-
rectly to an embedded figures problem. Twenty-eight per-
cent of the subjects tested in the afternoon sessions were
correct, compared to 13% of those tested in the morning.
The authors concluded that intersubject communication ac-
counted for this difference in performance.

5. From these studies, three conclusions seem warranted.
First, rates of reported or actual disclosure vary considerably
and appear to be related to type of debriefing, delay follow-
ing the experiment, and whether or not the discloser be-
lieves the target is a potential subject. The effects of other
factors on disclosure, such as liking for the experiment, have
not been investigated. Second, prior knowledge of experi-
mental procedure affects performance even when deception
is not an issue. Third, although disclosure rates may be high,
only a small proportion of subjects are affected by the leak-
age. In institutions with small subject pools, however, the
problem may be more severe than in large institutions in
which multiple sections of the introductory course supply
potential participants.
Taken together, these earlier studies suggest that con-
tamination occurs and that results may be tainted. Our ex-
periments investigated several variables that might affect
undergraduates' willingness to comply with an experiment-
er's request not to discuss their participation. In the first
experiment, we examined the relation between beliefs about
the scientific value of participation, general evaluation of
the experience, and likelihood of disclosure. In the second
experiment, we asked half the participants in a laboratory
experiment to sign a pledge to keep the experimenter's con-
fidence. In the third experiment, we telephoned these same
participants to see whether the passage of time or promises of
anonymity would affect disclosure.
Experiment 1
Method
Sixty-five introductory psychology students volunteered
to participate in the experiment, for which they received 112
hr of experimental credit. Students in the course have the

6. option of writing a 3-page review of a recent journal article
or serving as subjects for a total of 3 hr. Subjects read brief
descriptions of two different studies. The first study used a
Scholastic Aptitude Test (SAT) type task presented on a
computer. The second study was a perceptuomotor tracking
task. Only the procedures were described; no rationale for
the studies was presented. Both descriptions concluded with
a statement that the experimenter requested that partici-
pants not discuss the experiment with others "because the
results might be affected if other psychology students who
might participate in the study found out what it was about."
Following each scenario were six questions asking: (a) how
much the respondent would enjoy participating in such a
study, (b) whether the respondent thought the experiment-
er would find anything interesting, (c) the importance of
complying with the request for confidentiality, (d) the like-
lihood the respondent would talk about the experiment with
another student in the subject pool, (e) the likelihood the
respondent would talk about the experiment with another
student not in the pool, and (0 whether the respondent
would expect to learn anything from participating. Each
question was followed by a 7-point response scale ranging
from not at all likely (1) to extremely likely ( 7 ) .
Resulfs and Discussion
A 2 x 6 (Items x Scenario) analysis of variance
(ANOVA) was performed. There were, of course, dif-
ferences in responses to the items, F(5, 315) = 34.51, p <
.001, but the only other significant effect was the Scenario
x Item interaction, F(5, 315) = 3.36, p < .005. Inspection
of the means indicated that students believed they would
enjoy participating in the SAT study (M = 3.8) less than in
the tracking task study (M = 4.4). Consistent with Britton's
( 1 987) findings, the means on the items measuring the value

7. of the studies did not indicate negative evaluations. The -
mean response to the question of whether the experimenter
might discover something interesting was 4.4 for the SAT
and 4.7 for the tracking task. For the issue of whether the
participants would learn anything, the mean for the SAT
was 3.9 and 3.6 for the tracking task. Students perceived the
importance of confidentiality (M = 5.9 for the SAT; M =
5.7 for the tracking task), but indicated some likelihood (M
= 2.4 for the SAT; M = 2.7 for the tracking task) that they
would talk to another student who was in the subject pool.
The likelihood of talking to a student not in the subject pool
was greater (M = 4.2 for the SAT; M = 4.1 for the tracking
task).
To determine the relation among the items, we con-
ducted separate principal component factor analyses for
each scenario. In both cases, two factors emerged. The eval- -
uative items (enjoyment, learning opportunity, and like-
lihood of scientific discovery) loaded together on Factor 1 in
both analyses; all had factor loadings greater than .75. Both
of the likelihood of talking items appeared together on Fac-
tor 2, with loadings in excess of .80. The item assessing
views of the importance of complying with the experiment-
er's request showed weaker loadings on the first factor (.55
and .56) and low, negative loadings on the second (-. 11
and -. 19). This factor pattern indicated that the evaluative
items and the likelihoc~d of talking items were not
correlated.
The results of our first experiment suggest that evaluative
judgments concerning the merits of an experiment are unre-
lated to whether or not subjects believe that honoring an
experimenter's request for confidentiality is important. Fur-
thermore, there is no relation between the latter belief and
likelihood of revealing information to others. In general,
respondents indicated a fairly positive evaluation of the re-

8. search scenarios but high likelihoods of not honoring an
experimenter's request for confidentiality.
Experiment 2
In this experiment, we observed actual disclosure behav-
ior as contrasted with students' self-reports. All our subjects
served initially in either the SAT computer study or the
perceptuomotor tracking task. Subsequently, a confederate
made a direct request for information. We also wanted to
determine if signing an agreement would inhibit disclosure.
Vol. 17, No. 3, October 1990
Walsh and Stillman (1974) found less disclosure when sub-
jects were sworn t o secrecy but Diener, Kelem, Beaman, and
Fraser (cited in Diener et al., 1972) did not.
Method
Twenty-eight students enrolled in the introductory psy-
chology course, who had not served in our first role-playing
experiment, participated in the second. These students were
selected from a group of 102 participants described in our
first experiment. T h e 28 subjects (13 men and 15 women)
were selected because they were scheduled for the
SATJtracking experiment at a time when one of our two
confederates was available.
As part of t h e debriefing, we asked all subjects not to
discuss their experiences with anyone else, ~ a r t i c u l a r l ~
oth-
ers who might be future participants (i.e., other introducto-
ry psychology students). In addition, 12 of the subjects were

9. asked to sign a n agreement stating that they understood the
request and agreed to comply. Three different experimenters
conducted the debriefings. T h e y were counterbalanced
across the two experimental conditions.
After t h e debriefing, the subject was asked to sit o n a
bench outside the experimental room while the experiment-
er went t o the psychology office to get the form t h e subject
needed to verify participation. A female confederate was
already seated o n t h e bench when the subject arrived. After
the experimenter left, the confederate told the subject that
she was a student in a n introductory psychology course who
had not participated in any experiments and wanted to know
what it was like t o be in one. She asked the subjects to
describe the experiment they had just left. T h e amount each
subject disclosed was rated o n a 3-point scale ranging from no
disclosure ( 0 ) t o full disclosure (2) by the confederate and
the
first author, both of whom were blind as to whether or not
the subject had signed a pledge not to talk. Interrater relia-
bility, using gamma, was .899.
Results and Discussion
W e were surprised to discover that more than one third of
our subiects revealed something to the confederate, even -
though t h e experimenter was in t h e adjacent office and was
expected t o return at any moment. In two instances, the
experimenter stood by while the subject finished a disclosure
to the confederate. W e were also chagrined when a student
not scheduled as one of our subjects entered the S A T experi-
ment with the question, "Is this the experiment where I sign
the paper promising not t o talk?"
Of the 12 subjects who signed a n agreement, 1 1 refused to
reveal any information to the confederate and 1 subject gave

10. some disclosure. but n o one wrovided detailed information.
In this condition, we witnessed our only fabrication: O n e
atudent told the confederate she would be wired to a ma-
chine and "shocked like hell." Of the 16 subjects asked to
honor the exwerimenter's request for nondisclosure but not
asked to sign a n agreement, 7 gave n o disclosure, 3 gave
partial disclosure, and 6 gave detailed disclosure t o the con-
federate. T o ensure adequate expected values, we collapsed
the full- and partial-disclosure cells and performed a chi-
square test, which indicated that signing the agreement In-
hibited subsequent disclosure, x Z ( l , N = 28) = 6.86 P <
.01. O u r actual disclosure rate 5 min after the debriefing and
not more than 50 ft from the experimenter came as a sur-
prise. Thirty-nine percent of our subjects disclosed informa-
tion t o a self.identified subject who was shopping for experi-
mental credits.
Experiment 3
Although signing a n agreement appeared to increase
compliance in the short run, we were concerned about its
effectiveness over a longer period. W e were also interested
in how much disclosure would occur when respondents
knew such information had the to contaminate the
entire subject pool.
Method
Two to 3 weeks after participating in the second expert-
ment, 10 of the signers and 10 of the nonsigners were tele-
phoned by a female research assistant blind to the
experimental conditions. T h e caller introduced herself as an
undergraduate psychology major who was writing an article
o n t h e research experiences of students enrolled in introduc-
tory psychology. T h e article would appear in the student

11. newspaper during the same semester in which the students
had served as subjects.
For each experiment in which they had participated, the
subjects were asked what they had been required to do, what
they thought the researcher was trying to figure out, and
whether they thought the experiment was a worthwhile ex-
perience. Half the subjects were told that thetr responses
would be anonymous, and half were asked to Lrerify their
name so that they could be quoted in the article. The degrer
of detail that subjects disclosed was rated o n a 5-point scale
ranging from no disclosure ( 0 ) to full disclosure (4).
A t the conclusion of the third experiment, we sent all
subjects who had participated in our second experiment ; I
postcard stating:
Following your participation In an experiment In 635 Poe
Hall, you were approached, and in some cases telephoned,
by one of our research assistants who asked you tc) descrihe
your research experiences. The purpose of these ~nquirteh
was to evaluate the effectiveness of our debriefing tech-
niques. As in the experiments themselves, your responses
cannot be linked to you as an individual. We thank y o u for
your cooperation.
W e also provided the name and telephone number of thc
supervising faculty member.
Results and Discussion
N o subject was able to glve a coherent explandt~on of the
researcher's goals. T h e most common response was to "we
how we would d o o n those ktnds of problem5 " All the
subjects belleved the experiment had been worthwhtle, ,ll-
though one sald "worthwhlle for the experimenter, but not

12. for me " Seventeen of the 20 5uhjects descrthed the pro
Teaching of Psychology
cedure t o varying extents. Four indicated that they were
asked not t o discuss their participation but "guessed it was
alright now." Students who were guaranteed anonymity re-
vealed more (M = 2.27) than did those whose names were
verified ( M = 1.00), t(18) = 2.39, p < .05. Signing or not
signing a n agreement in t h e actual experiment had no effect
o n disclosure. Magnitude of initial disclosure t o t h e
confed-
erate did not predict magnitude of disclosure in the tele-
phone interview. As in Experiment 1, evaluation of the
experience was unrelated t o disclosure.
General Discussion
O u r results paint a pessimistic picture of how undergradu-
ates honor the clause of our research contract that holds
them responsible for not discussing t h e details of their par-
ticipation with anyone who might later serve as a subject. In
our first study, 22% of the role-players indicated that they
would probably n o t honor the experimenter's request not t o
discuss t h e procedure with a potential subject. In the second
experiment, 39% of our subjects gave at least some dis-
closure t o a confederate. In the third experiment, after a 2 -
week interval, 85% of these participants disclosed informa-
tion that could contaminate the entire subject pool. These
rates are particularly alarming, given that our subjects re-
vealed information t o a stranger. Even more disclosure
might occur with friends or classmates. T h e student who
asked about t h e nondisclosure pledge presumably had re-
ceived such information.

13. W e identified several factors that seem t o affect disclosure
rates. Asking subjects t o sign a pledge decreased immediate
but not later disclosure t o a confederate. Promising students
anonymity increased disclosure rates, suggesting a n
awareness t h a t such disclosure might have damaging effects.
Neither liking for t h e research nor a belief that it was impor-
t a n t was related t o compliance with the experimenter's re-
quest for confidentiality.
Does this research suggest any improvements in debriefing
t h a t might decrease t h e frequency of disclosure? Asking
par-
ticipants t o sign a n agreement reduced disclosure t o a
poten-
tial subject in the short run, but this commitment had n o
effect o n later willingness t o contaminate the entire pool.
Perhaps providing more information about the tasks would
have proved effective. T h e tasks used in Experiment 2 in-
volved no deception, and the studies' rationales were de-
scribed a t length. Nevertheless, none of our subjects was
able, 2 weeks later, to describe the researcher's goals. If we
had used a more extensive debriefing, subjects may have felt
a greater stake in the outcome and been less revealing when
questionned. Using the collaborative model that Korn
(1988) described might decrease intersubject communica-
t ion.
O u r findings regarding the ability of introductory psychol-
ogy instructors t o minimize subject pool contamination are
discouraging. Results of our first study suggest that apprecia-
tion of the potential scientific contribution of undergradu-
ates, as Kimble (1987) suggested, is unrelated to honoring a
request not t o disclose, although such a n emphasis may im-
prove overall attitudes toward t h e research experience.

14. A final issue concerns our own adherence t o the contract.
Experiments 2 and 3 involved deception by the confederate.
W e argue that there were n o realistic alternatives for study-
ing t h e extent t o which subjects reveal information about
their research experiences. Results of Experiment 1 , in
which students role-played t h e same tasks we used in Experi-
ment 2, indicate that they underestimated the amount of
disclosure that actually occurred. Our own ethical difficulty
arose in trying t o settle o n the language t o use o n the
postcard. W e took care not t o suggest that students had
violated their promises.
In conclusion, our experiments suggest that subject pool
contamination is a problem. Researchers whose work re-
quires naive participants need to ascertain the extent of their
subjects' prior knowledge of the experimental tasks and
procedures.
References
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Psychological Reports, 19, 238.
Britton, B. K. (1987). Comment on Coulter and Daniel.
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Diener, E., Matthews, R . , & Smith, R. (1972). Leakage of
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mental information to potential future subjects by debriefed
sub-
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Levy, L. H. (1967). Awareness, learning, and the beneficient
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Notes
1. We thank Kim Toussignant, Gabie Smith, and Stella
Anderson
who helped collect and analyze these data.
2. Requests for reprints should be sent to Kitty Klein,
Department
of Psychology, North Carolina State University, Box 7801,
Raleigh, N C 27695-7801.
Vol. 17, No. 3, October 1990