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We dont know what normal hdl levels are expressed in

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We don’t know what normal HDL levels are, expressed in numerical terms, so we don’t know what a “60 percent drop” amounts to, or whether a drop of 60 percent from a normal level produces a level that’s too low. However, the implication of the article is that the drop is medically important. It certainly would be nice to know something more about the “self-prescribed and self- administered use” of steroids. Was the overall drop in HDL due to a very large drop on the part of two very heavy users? Well, probably not, given the source of the study and where it was published. 11. First study: The hypothesis is that vasectomies don’t cause disease. It’s a nonexperimental cause-to-effect study. Over 10,000 men were in each of the groups (with and without vasectomies). Given the sources, we think it’s safe to assume that the report of “similar” rates of disease in the two groups means that there was no statistically significant difference in frequency between them. Second study: The hypothesis here is that vasectomies do not cause heart disease. It’s a nonexperimental cause-to-effect study. We figure the “same” incidence of heart disease in the two groups indicates no statistical significance, as in the previous study. The report does not mention steps taken to insure similar treatment of control and study groups, but this is probably a failure of the report and not the study. We think the conclusion here, as in the first study, is reliable. Both of us certainly hope so. 12. The causal hypothesis is that radiation-induced tumors are prevented by dietary restrictions in rats exposed to high doses of X-rays; controlled, cause-to-effect experiment. Forty-four rats in the experimental group; an undisclosed number in the control group. The difference in frequency of effect (no tumors) was 80 percent (80 in the experimental group vs. 0 in the control group). The study strongly supports the hypothesis. IM – 11 | 10
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13. Encephalitis has declined in California during the past thirty years because more people are staying inside from 7 p.m. to 10 p.m. with their air conditioners on, watching television. There is confusion either in this investigation or in the report of the investigation. In order to establish a causal relationship between staying indoors and not getting encephalitis, one would have to show that there would be fewer cases of the disease if everyone stayed indoors than if no one did. But you could establish a correlation between staying indoors and not getting encephalitis merely by showing that the encephalitis rate was lower among those who stayed indoors than among those who didn’t, and this is apparently what the investigation attempted to do. However, that even this simple correlation was shown by the investigation is not clear from the report, because, according to the report, television ownership was compared with the encephalitis rate, not television viewing. Further, the statistics quoted—that 79 percent of the
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We dont know what normal HDL levels are expressed in...

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