chapter 9 exercise

chapter 9 exercise - 9.1 Cell phones and brain cancer A...

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9.1 Cell phones and brain cancer. A study of cell phones and the risk of brain cancer looked at a group of 469 people who have brain cancer. The investigators matched each cancer patient with a person of the same sex, age, and race who did not have brain cancer, then asked about use of cell phones. 2 Result: “Our data suggest that use of handheld cellular telephones is not associated with risk of brain cancer.” Is this an observational study or an experiment? Why? What are the explanatory and response variables? This is an observational study. Explanatory variable : cell phone usage. Response variable : presence/absence of brain cancer. 9.5 Growing in the shade. Ability to grow in shade may help pines found in the dry forests of Arizona resist drought. How well do these pines grow in shade? Plant pine seedlings in a greenhouse in either full light, light reduced to 25% of normal by shade cloth, or light reduced to 5% of normal. At the end of the study, dry the young trees and weigh them. Individuals : pine seedlings. Factor : amount of light. Treatments : full light, 25% light, or 5% light. Response variable : dry weight at the end of the study. 9.13 Arsenic and lung cancer. Arsenic is frequently found both in the natural environment and in food. A study of the relationship between arsenic in drinking water and deaths from lung cancer measured arsenic levels in drinking water in 138 villages in Taiwan and examined death certificates to identify lung cancer deaths. The study summary says that “arsenic levels above 0.64 mg/l were associated with a significant increase in the mortality of lung cancer in both genders, but no significant effect was observed at lower levels.” 6 (a) Explain why this is an observational study rather than an experiment . (b) The word “significant” in the conclusion has its statistical meaning, not its everyday meaning. Restate the study conclusion without using the word “significant” in a way that is clear to readers who know no statistics .
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(a) The researchers simply observed the existing arsenic levels; they did not alter them. (b)
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chapter 9 exercise - 9.1 Cell phones and brain cancer A...

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