Chapter-11

# Im 11 7 1 there are three causal hypotheses mentioned

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Exercise 11-16 1. There are three causal hypotheses mentioned: One is that drinking wine weekly or monthly may cause dementia; a second is that drinking wine daily probably does not prevent dementia; and the third is that regular beer drinking is probably a cause of dementia. The study is cause-to-effect, but the study is largely nonexperimental because of the self- selection of the experimental group(s)—i.e., the drinkers—and the control group—the nondrinkers. Nothing is mentioned of the nature or size of either group. The description of the study is quite vague. Although the source of the study appears to be a legitimate authority, the account given here would lead us to want more details of the study before we’d give more than a very tentative acceptance of the results. 2. a. Piano instruction produces better performance on ratios and fractions. b. We can’t tell if it’s a true controlled experiment because we don’t know if the kids were divided into their respective groups. If it was done randomly, then it’s a cause-to-effect experiment. In any case, it’s cause-to-effect. c. The groups with the various training were experimental; the group with none was the control group. d. The difference in effect is 15-41%. Since we don’t know whether most were nearer 15% or nearer 41% or neither, we can’t say just what the d is in this case. e. We don’t know much about control of variables given the skimpiness of this report. f. We’d say there is some reason to suspect an influence of the musical training on the test outcome, but we’d be very cautious, especially given the small numbers given here. It takes a lot to be statistically significant when your groups are less than 30, as is the case here. 3. We’ll summarize here (the details are obvious from the items themselves): We can’t say with confidence that the day-care programs caused an increase in performance because we are not given the numbers nor the degree of difference in performance. But there’s reason to believe the results are at least possibly significant simply because the report appears in a substantial journal devoted to this subject and the fact that the study, a cause-to-effect experiment, included randomly divided experimental and control groups. 4. Causal claim: Sleeping in a room with a light until age two is a cause of nearsightedness in later years. The study is nonexperimental, cause-to-effect. No differences between the experimental groups (children who slept with lights on) and the control group (children who slept in darkness). The differences in effect were 24 percent between night light and darkness, and 45 percent between a lamp and darkness. From what is reported, no problems can be identified. Although the study is fairly small, the results indicate it is likely that there is a causal connection between the described cause and effect—a d of about 11 percent would be necessary in an experimental study; the higher numbers here help compensate for the nonexperimental nature of the study. The differences could also be explained if nearsighted
• Spring '13
• Newman
• Causality, heart attack, Presumed cause

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