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Informed Consent: III. Informing Subjects That Performance Will Not Affect Credit May Affect Performance

Concern has been voiced about possible experimental effects of the information conveyed to subjects during the informed consent procedure (Gardner, 1978). The present study investigated the impact of informing college students who were volunteering for credit that their performance would not affect amount of credit, a stipulation often imposed by institutional review boards. Sixty undergraduate psychology students volunteered and were randomly assigned to two groups. Subjects in one group were informed in writing immediately prior to testing that their performance would not affect their credit, while those in the other group were not informed of any relation between performance and credit. Subjects then completed the Plake and Parker (1982) Revised Mathematics Anxiety Rating Scale and a 25-item Cchoice test of multiplication. No differences were observed in anxiety scores between the informed ( M = 69.3, SD = 22.97) and the noninformed groups ( M = 67.5, SD = 23.22), but the informed group solved significantly fewer multiplication problems correctly ( M = 19.13, SD = 4.58) than the noninformed group (M = 21.80, SD = 2.20; t = 2.83, p < .01). In the informed group, nine subjects with high anxiety about mathematics solved 60% or fewer multiplication problems correctly, leading to a significant correlation between multiplication performance and the anxiety scores (r = -.55). In the noninformed group, no subject solved fewer than 72% of the multiplication problems correctly and the correlation between multiplication and the anxiety scores was -.05. It appears that the informed consent procedure may have selectively undercut the motivation of the subjects anxious about mathematics and brought about a potentially spurious correlation.