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**Unformatted text preview: **doesn’t. If this is true, the two variables are said to be independent. In the last example above, the null hypothesis says that stretching prior to exercise (explanatory variable) does not increase or decrease the rate of injury during exercise (response variable). The alternative hypothesis, says that stretching does affect the rate of injury. In a chi- square test of independence, the null hypothesis always claims that there is no relationship between the explanatory and response variables. Example An experiment is designed to test the side- effects of Nicorette gum, which is used by people who are trying to quit smoking. One possible side effect is a sore throat. The study is a randomized experiment involving 300 subjects. They are divided into two groups of 150. One group chews Nicorette for a week; the other group chews a placebo gum....

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