Indicate whether each of the following studies is an experiment or an observational study. If it is an experiment, identify the independent variable and note any possible confounding variables.

(a) A psychologist uses chimpanzees to test the notion that more crowded living conditions trigger aggressive behavior. Chimps are placed, accord-ing to an impartial assignment rule, in cages with either one, several, or many other chimps. Subsequently, during a standard observation period, each chimp is assigned a score based on its aggressive behavior toward a chimp-like stuffed doll.

(b) An investigator wishes to test whether, when compared with recognized, professional scientists, recognized, professional artists tend to be born under different astrological signs.

(c) To determine whether there is a relationship between the sexual codes of primitive tribes and their behavior toward neighboring tribes, an anthropologist consults available records, classifying each tribe on the basis of its sexual codes (permissive or repressive) and its behavior toward neigh-boring tribes (friendly or hostile).

(d) In a study of group problem solving, an investigator assigns college stu-dents to groups of two, three, or four students and measures the amount of time required by each group to solve a complex puzzle.

(e) A school psychologist wishes to determine whether reading comprehension scores are related to the number of months of formal education, as reported on school transcripts, for a group of 12-year-old migrant children.

(f) To determine whether Graduate Record Exam (GRE) scores can be increased by cramming, an investigator allows college students to choose to participate in either a GRE test-taking workshop or a control (non-test-taking) workshop and then compares the GRE scores earned subsequently by the two groups of students.

(g) A social scientist wishes to determine whether there is a relationship between the attractiveness scores (on a 100-point scale) assigned to college students by a panel of peers and their scores on a paper-and-pencil test of anxiety.

(h) A political scientist wishes to determine whether males and females differ with respect to their attitudes toward defense spending by the federal government. She asks each person if he or she thinks that the current level of defense spending should be increased, remain the same, or be decreased.