INTRODUCTION Since the 1930s, a number of studies have been performed on cognitive sex differences. Two widely researched cognitive sex differences are found in tasks involving verbal fluency and visual-spatial ability. Although at the present time research in this area remains inconsistent and inconclusive, the general finding has been that males perform better on visual-spatial tasks, while females perform better on verbal tasks. Results may vary according to the operational definition of these two cognitive abilities. For the purposes of this study, “verbal fluency” is defined as the ability to recall associated words from memory, while “visual-spatial” is defined as the ability to discern the relationship between relative space and objects. Maccoby & Jacklin (1974) were among the first to show a significant difference between male and female performance on verbal fluency and visual-spatial tasks. However, other studies have shown moderate to no differences. Using an experimental process known as meta-analysis, Hyde (2001) found no sex differences in verbal abilities and only moderate differences in spatial ability. In a more recent study performed on university students, Weiss (2003) found that although women perform better on verbal tasks and men perform better on spatial tasks, the effect sizes are small. Research has also shown that males perform better on some verbal tasks, such as verbal analogies, while females perform better on some quantitative tasks. Social and environmental factors have been found to play a role in male and female cognition. Zajonc and Markus (1975) were the first to propose this idea with what is known as the confluence model. The main feature of the confluence model is that the individual is considered part of his or her own environment and is constantly being influenced by it. This supports the idea that intelligence is dependent on intellectual environment, including number of siblings, birth order, and age spacing. In addition, other factors such as genetic background and child-rearing practices can have an effect as well. Downey (1995) based his research on educational performance on a resource-dilution model, which assumes a direct relationship between intelligence and parental resources. Downey found that parental resources (or the lack thereof) explain the inverse relationship between sibship size and educational performance. This data supports the resource-dilution model and its prediction that as the number of children increases, the proportion of parental resources for each child decreases, thus decreasing the potential for higher learning and intelligence. The introduction of these two models has instigated more research on the effects of social and environmental effects on intelligence and cognitive abilities. Numerous studies have shown an inverse relationship between family size and IQ, while a significant negative correlation was found between family size and GPA (Marjoribanks 1973). More specifically, Vonderheide (1978) found that subjects with four or less siblings had a higher GPA than subjects with four or more siblings. If verbal and spatial tests vary by gender, than a logical implication of the confluence model is that sex composition should affect these abilities as well. Based on data from standardized tests showing that males perform better than females overall, the model would imply that children with more brothers have an intellectual advantage over children with more sisters. Powell and Steelman (1990), however, did not find a significant difference between math and verbal components in relation to the number of brothers versus the number of sisters. In the same study, though, it was found that, concerning academic performance, an additional brother significantly lowers one’s GPA, while an additional sister has only a slight influence. The purpose of this study is to further investigate the effects of family size and sex composition on male and female performance in verbal fluency and visual-spatial tasks. Parenting style (whether the individual was raised by a single mother, single father, or both parents) will also be considered as an additional independent variable.
METHODParticipants Data was collected from 47 students enrolled in an introductory psychology class. Participants included 17 males and 30 females, ranging in age from 18-46.
Materials A demographic sheet was distributed, consisting of the participant’s age, gender, total number of siblings, total number of male and female siblings, and by whom they were raised (see Appendix A). The demographic sheet also consisted of a number between 1 and 70, which was used to keep the individual’s information together while maintaining confidentiality. A verbal fluency task and a visual-spatial task were used as a baseline for comparison with all of the independent variables. The verbal fluency task required the participants to write as many words as they could think of that begin with the letter “m”. This was recorded on the bottom half of the demographic sheet. The visual-spatial task consisted of two sheets of paper stapled back-to-back. The first sheet of paper consisted of a grid of twenty boxes with a picture in each box (see Appendix B). The second piece of paper consisted of a similar grid of twenty blank boxes (see Appendix C).
Procedure The participants were given a few minutes to fill out the demographic sheet. I then facilitated the verbal fluency task for one minute. Upon completion of the task, I picked up the demographic sheets and passed out the materials for the visual-spatial task. The participants were given one minute to look at the pictures on the first page and another minute immediately following the first to write the word of the picture in the coinciding box on the second page.
RESULTS An independent samples t-test was calculated comparing verbal task mean scores and gender. No significant difference was found (t(45) = .105, p = .917. The mean score of the male participants (m = 13.71, sd = 3.62) was not significantly different from the mean of the female participants (m = 13.83, sd = 4.17). An independent samples t-test was calculated comparing spatial task mean scores and gender. A strong non-significant difference was found (t(45) = 1.97, p = .055. The mean score of the female participants (m = 9.96, sd = 3.44) was almost significantly higher than the mean score of the male participants (m = 7.65, sd = 4.55). The verbal task mean scores and the total number of siblings of each participant were compared using a one-way ANOVA. No significant difference was found (F(4,42) = .558, p = .695. The total number of siblings of each participant did not have a significant effect on their verbal task score. The spatial task mean scores and the total number of siblings of each participant were compared using a one-way ANOVA. No significant difference was found (F(4, 42) = 1.159, p = .343. The total number of siblings of each participant did not have a significant effect on their spatial task score. The verbal task mean scores and the relative number of brothers and sisters of each participant were compared using a one-way ANOVA. No significant difference was found (F(2, 44) = 1.049, p = .359. The relative number of brothers and sisters of each participant did not have a significant effect on their verbal task score. The spatial task mean scores and the relative number of brothers and sisters of each participant were compared using a one-way ANOVA. No significant difference was found (F(2, 44) = .082, p = .921. The relative number of brothers and sisters of each participant did not have a significant effect on their spatial task score. The verbal task mean score and the parenting style of each participant were compared using a one-way ANOVA. No significant difference was found (F(3, 43) = 2.994, p = .041. The parenting style of each participant did not have a significant effect on his or her verbal task score. The spatial task mean score and the parenting style of each participant were compared using a one-way ANOVA. No significant difference was found (F(3, 43) = .086, p = .968. The parenting style of each participant did not have a significant effect on his or her spatial task score.
DISCUSSION The results did not support the hypotheses and were not significantly different. This is inconsistent with previous research for all hypotheses. A non-significant trend was found for an initial comparison between spatial task mean scores and gender. This seems to be consistent with previous research, as little to no differences has been found in visual and spatial task performance (Hyde 2001). Where significant differences have been shown, females performed better on verbal tasks and males performed better on spatial task. In this study, female scores were higher for both tasks. The total number of siblings did not have a significant effect on verbal and spatial task performance and were inconsistent with previous research. For both tasks, participants with a greater number of siblings scored higher than participants with fewer siblings. The resource-dilution model, however, predicts an inverse relationship between sibling size and task performance. These results are also inconsistent with those of Vonderheide (1978), who found that participants with four or less siblings had a higher GPA than subjects with four or more siblings. The data comparing relative number of brothers and sisters and task performance were not significant. Powell and Steelman (1990) found a significant difference in that an additional brother lowers one’s GPA, although an additional sister has little to no effect on academic performance. In this study, participants with more brothers had higher scores on the verbal task but produced lower scores on the spatial task than participants with more sisters or an equal number of brother and sisters. These results are inconsistent with the initial hypothesis that participants with more sisters would have higher verbal scores, and participants with more brothers would have higher spatial scores. Participants raised by both parents scored higher on the verbal fluency task than participants raised by a single parent, as stated in the initial hypothesis; however, the results were not significant. The data comparing parenting style and spatial task performance was found to be inconsistent with the hypothesis, in that participants raised by a single father scored higher than participants raised by both parents and a single mother. A larger sample size with more variability may have produced significant results for all hypotheses. Small variability, especially in the data on parenting style, may have had an effect on the results. Out of the 47 participants, 33 were raised by both parents, 10 were raised by a single mother and 2 were raised by a single father. Small variability was evident in the data on total number of siblings as well, in that over half of the participants had 1-2 siblings. A larger, more variable sample size may have produced more proportional and significant data. For further research, it is suggested that the data on total number of siblings and relative number of brothers and sisters be broken down into single categories, such that one category equals 1 sibling, another category equals 2 siblings, and so on. Results may have been significant had the data not been grouped together.
REFERENCESDowney, D.B. (1995). When bigger is not better: family size, parental resources, and children’s educational performance. American Sociological Review, 60, 746-761.
Hyde, J. (1990). Meta-analysis and the psychology of gender differences. Signs: Journal of Women in Culture & Society, 16, 55-74.
Maccoby, E.E. & Jacklin, C.N. (1974). The Psychology of Sex Differences. Stanford, CA: Stanford University Press.
Majoribanks, K. (1976). Sibsize, family environment, cognitive performance, and affective characteristics. Journal of Psychology: Interdisciplinary & Applied, 94, 194-204.
Powell, B. & Steelman, L. (1990). Beyond sibship size: sibling density, sex composition, and educational outcomes. Social Forces, 69, 181-206.
Vonderheide, S.G. (1978). Birth order and college grade point average. Psychological Reports, 42, 150-154.
Weiss, E.M. (2003). Sex differences in cognitive functions. Personality & Individual Differences, 35, 863-875.
Zajonc, R.B. & Markus, G.B. (1975). Birth order and intellectual development. Psychological Society, 82, 74-88.
APPENDIX ADemographic sheet
Please circle one:
Gender: Male Female
Total number of siblings: 0 1-2 3-4 5-6 6 or more
Number of male siblings: 0 1-2 3-4 5-6 6 or more
Number of female siblings: 0 1-2 3-4 5-6 6 or more
Were you predominantly raised by your:
Mother Father Both parents Other
APPENDIX BFirst page of visual-spatial task
APPENDIX CSecond page of visual-spatial task
FIGURE CAPTIONSFigure 1. Total number of siblings and verbal/spatial task scores.
Figure 2. Relative proportion of male and female siblings and verbal/spatial task scores.
Figure 3. Parenting style and verbal/spatial task scores.