In each of the following descriptions of research studies, you are to identify the independent variable(s). You should also be able to identify at least one dependent variable in each study.

A. A psychologist was interested in the effect of food deprivation on motor activity. She assigned each of 60 rats to one of four conditions differing in the length of time for which the animals were deprived of food: 0 hours, 8 hours, 16 hours, 24 hours. She then measured the amount of time the animals spent in the activity wheel in their cages.

B. A physical education instructor was interested in specifying the changes in motor coordination that occur as children gain experience with large playground equipment (e.g., slides, swings, climbing walls). For a span of 8 weeks, preschool children were assigned to 4, 6, or 8 hours per week for time allowed on the equipment. She then tested their motor coordination by asking them to skip, jump, and stand on one foot.

C. A developmental psychologist was interested in the amount of verbal behavior very young children displayed depending on who else was present. The children in the study were 3 years old. These children were observed in a laboratory setting for a 30-minute period. Half of the children were assigned to a condition in which an adult was present with the child during the session. The other half of the children were assigned to a condition in which another young child was present during the session with the child being observed. The psychologist measured the number, duration, and complexity of the verbal utterances of each observed child.