21.4 Another investigator criticizes the design of the previous study, saying that high school students should have been randomly assigned to either the special training condition or a control condition and tested just once at the end of the study. Subsequently, she conducts this study.
21.7 An investigator wishes to test whether creative artists are equally likely to be born under each of the 12 astrological signs.
21.8 To determine whether there is a relationship between the sexual codes of primitive tribes and their behavior toward neighboring tribes, an anthro-pologist consults available records, classifying each tribe on the basis of its sexual codes (permissive or repressive) and its behavior toward neighboring tribes (friendly or hostile).
21.12 Over a century ago, the British surgeon Joseph Lister investigated the relationship between the operating room environment (presence or absence of disinfectant) and the fate of about 100 emergency amputees (survived or failed to survive).
21.13 A comparative psychologist suspects that chemicals in the urine of male rats trigger an increase in the activity of other rats. To check this hunch, she randomly assigns rats, in equal numbers, to either a sterile cage, a cage sprayed with a trace of the chemicals, or a cage sprayed thor-oughly with the chemicals. Furthermore, to check out the possibility that reactions might be sex-linked, equal numbers of female and male rats are assigned to the three cage conditions. An activity score is recorded for each rat during a 5-minute observation period in the speciï¬ ed cage.
21.14 A psychologist wishes to evaluate the effectiveness of relaxation training on the subsequent performance of college students in a public speaking class. After being matched on the basis of the quality of their initial speeches, students are randomly assigned either to receive relaxation training or to serve in a control group. Evaluation is based on scores awarded to students for their speeches at the end of the class.
21.15 An investigator wishes to determine whether, for a random sample of drug addicts, the mean score on the depression scale of a personality test differs from that which, according to the test documentation, represents the mean score for the general population.
21.16 Another investigator wishes to determine whether, for a random sample of drug addicts, the mean score on the depression scale of a personality test differs from the corresponding mean score for a random sample of nonaddicted people.
21.17 To determine whether cramming can increase GRE scores, a researcher randomly assigns college students to either a specialized GRE test-taking workshop, a general test-taking workshop, or a control (non-test-taking) workshop. Furthermore, to check the effect of scheduling, students are randomly assigned, in equal numbers, to attend their workshop either during a marathon weekend or during a series of weekly sessions.
21.18 A criminologist suspects that there is a relationship between the degree of structure provided for paroled ex-convicts (a supervised or unsuper-vised â€œrehabâ€ house) and whether or not there is a violation of parole during the ï¬ rst 6 months of freedom.
21.19 A psychologist uses chimpanzees to test the notion that more crowded living conditions cause aggressive behavior. The same chimps live in a succession of cages containing one, several, or many other chimps. After several days in each cage, chimps are assigned scores on the basis of their aggressive behavior toward a chimplike stuffed doll in an observation cage.
21.20 In an extrasensory perception experiment involving a deck of special playing cards, each of 30 subjects attempts to predict the one correct pattern (on each playing card) from among ï¬ ve possible patterns during each of 100 trials. The mean number of correct predictions for all 30 subjects is compared with 20, the number of correct predictions per 100 trials on the assumption that subjects lack extrasensory perception.
21.21 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.