Within Group Differences - 2 Groups: Examples
EXAMPLE 1: Suppose you are interested in men's and women's comparative performance on different tasks that are scored in the same way and that tap into abilities thought to differ between men and women. For example it has been found that, compared to women, men have slightly better spatial ability, whereas women have slightly better verbal ability (see references below). You would be looking not just for a male-female - BETWEEN GROUP - difference on either type of task. You would also be interested in whether the women tended to have higher scores on verbal than the spatial tasks - a WITHIN GROUP comparison. Similarly you would expect the men to do better on spatial than the verbal tasks.
EXAMPLE 2: You might be interested in whether two groups of people with memory problems of different origin have the same or different problems remembering things under different conditions, say when at home and when in a strange place. It could be relevant to the kind of help a service should offer them. Both groups would be tested both at home and in a place unfamiliar to them, using the same memory test. The difference between scores on the memory test in the two places, within one of the groups, is a WITHIN-GROUP difference. There may also be BETWEEN GROUP differences on one or both tests. Note: In order to reduce the possibility of the first test enhancing performance on the second, you might give each participant the two tests one week apart, say, and you could also consider using a COUNTERBALANCED design.
Geary, D. C. (1996). Sexual selection and sex differences in mathematical abilities. Behavioral and Brain Sciences, 19, 229–247.
Maccoby, E. E., & Jacklin, C. (1974). The psychology of sex differences. Stanford, CA: Stanford University Press
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