Ollie wakes up one morning and can't remember who he is, where he works, or where he lives. A physician does not find anything physically wrong, although his friends say Ollie has been under stress recently. He is probably suffering from

According to research, social groups tend to range in size from two or three members to several dozen members. Why is this?

A) If groups were larger it would be impossible to interact with other members. B) If a group becomes too large conflict within the group becomes unavoidable. C) It would be difficult for members to find more people who are similar to them. D) It is too difficult to arrive at normative consensus when groups grow too large. E) The larger the social group, the greater the likelihood of destructive conflict.

A research study finds that 40-year-olds are better able to solve math problems than 80-year-olds. It is suspected that the differences in problem-solving ability result from the fact that 80-year-olds had fewer opportunities to study math and did not have access to calculators or computers. If true, the study has revealed:

a) experimenter bias. b) a placebo effect. c) age-related differences. d) cohort effects.