A study was conducted to investigate the effiectiveness of bicycle safety helmets in preventing head injury. The data consist of a random sample of 793 persons who were involved in bicycle accidents during a one-year period (Table E1.7).
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TABLE E1.7
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Wearing Helmet
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Head Injury
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Yes
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No
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Total
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Yes
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17
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218
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235
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No
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130
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428
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558
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Total
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147
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646
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793
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(a) Compute and compare the proportions of head injury for the group with helmets versus the group without helmets. What would be your conclusion?
(b) Calculate the odds ratio associated with not using helmet. Does this result support your conclusion in part (a)?