| Prevalence vs. Incidence
Solution for Exercise B
1. Students #4, #9, and #16 begin smoking during this time, and ten other students were already smoker sand therefore not at risk for becoming smokers, so the incidence rate is 3 / (110-10) or 3.0 %.
2. Nine students were smoking at the time they graduated high school, for a prevalence rate of 9 / 110 or8.2 %.
3. If smoking behaviour among graduating seniors is the same as that for students who dropped out, then the results are good estimates. If smoking status is related to drop out status, then the results may be over or underestimates depending on whether those who finish high school are more or less likely to smoke than those who do not.
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