Identify each of the following as an independent-samples design or a paired-samples design. For each, identify the independent variable and its levels and the dependent variable. Work all six problems before checking your answers.

a. An investigator gathered many case histories of situations in which identical twins were raised apart-one in a "good" environment and one in a "bad" environment. The group raised in the "good" environment was compared with that raised in the "bad" environment on attitude toward education.

b. A researcher counted the number of aggressive encounters among children who were playing with worn and broken toys. Next, the children watched other children playing with new, shiny toys. Finally, the first group of children resumed playing with the worn and broken toys, and the researcher again counted the number of aggressive encounters. (For a classic experiment on this topic, see Barker, Dembo, and Lewin, 1941.)

c. Patients with seasonal affective disorder (a type of depression) spent 2 hours a day under bright artificial light. Before treatment the mean depression score was 20.0, and at the end of one week of treatment the mean depression score was 6.4

d. One group was deprived of REM (rapid eye movement) sleep and the other was not. At the sleep lab, participants were paired and randomly assigned to one of the two conditions. When those in the deprivation group began to show REM, they were awakened, thus depriving them of REM sleep. The other member of the pair was then awakened for an equal length of time during non-REM sleep. The next day all participants filled out a mood questionnaire.

e. One group was deprived of REM sleep and the other was not. At the sleep lab, participants were randomly assigned to one of the two groups. When those in the deprivation group began to show REM, they were awakened, thus depriving them of REM sleep. The other participants were awakened during non-REM sleep. The next day all participants filled out a mood questionnaire.

f. Thirty-two freshmen applied for a sophomore honors course. Only 16 could be accepted, so the instructor flipped a coin for each applicant, with the result that 16 were selected. At graduation, the instructor compared the mean grade point average of those who had taken the course to the GPA of those who had not to see if the sophomore honors course had an effect on GPA.