Gender Differences in Illusion Response: The Influence of Spatial Strategy and Sex Ratio - Statistical Data Included

Sex Roles: A Journal of Research,  Feb, 2001  by R. J. Miller

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Procedure

Four sign-up sheets were posted for this study, one for each of four consecutive evenings (Monday--Thursday). The scheduled time period for each evening's session was 7:30-9:30. No attempt was made to control the numbers of males and females signing up for any session--each student selected whichever of the four evenings he/she found most convenient. Thus, the proportion of males to females for each session was essentially randomly determined.

All four sessions were conducted in the same classroom by the same experimenter. After the participants for a given session were seated in the classroom, the first of two Ponzo illusion assessments occurred. The Ponzo task was administered following essentially the same procedure as in Experiment 1, using the same slides and response sheets, the same instructions, and the same scoring procedure. In the case of Experiment 2, however, the slides were projected onto a large screen in the front of the room. The projected images provided essentially the same contrast as in Experiment 1, but in Experiment 2 all image dimensions were greater by a factor of three.

Following the first Ponzo administration, participants engaged in a group hypnotic susceptibility task. This task was part of an unrelated experiment, and will not be further described, except to point out that it was a standard group screening procedure (Shor & Orne, 1962) that required about 75 min to complete. This task was followed by a 10-15 mm break, which was in turn followed by a second administration of the Ponzo task, using the same stimuli and instructions as the first Ponzo administration.

Results

The above procedure yielded a total of 240 data sets (111 males and 129 females). Table III shows descriptive statistics for the first Ponzo administration (Ponzo 1), the second Ponzo administration (Ponzo 2), and the composite Ponzo, as well as effect sizes for the male versus female comparisons. The Pearson r values for comparisons of Ponzo 1 with Ponzo 2 were .755 for all participants combined, .770 for males, and .684 for females, all significant at p [less than] .001.

A 2 x 2 (sex x Ponzo administration) ANOVA was conducted, with the two levels of sex being male and female, the two levels of Ponzo administration being Ponzo 1 and Ponzo 2, and the dependent variable being Ponzo score (percent illusion). The effect due to sex was significant, F(l, 238) = 31.14, p [less than] .001, as was the difference between Ponzo 1 and Poazo 2, F(l, 238) = 17.45, p [less than] .001. The interaction was not statistically significant.

In the course of analyzing the results, it became clear that chance had provided the opportunity to examine another variable, namely, sex ratio. It happened that the four sessions differed considerably in the relative numbers of males and females who participated, as follows: Monday (22 males, 39 females), Tuesday (31 males, 34 females), Wednesday (34 males, 25 females), Thursday (24 males, 31 females). Fig. 3 shows composite Ponzo values for males and females for each of the four sessions of the experiment, as well as the sex ratio (the proportion of males to females) for each session. A 2 x 4 (sex x session) ANOVA was conducted, showing significant results for sex, F(1, 232) = 33.56, p [less than] .001, and for session, F(3, 232) = 2.96, p = .03. However, there also was a significant interaction, F(3, 232) = 4.43, p = .005.