A 5-year prospective cohort study was conducted to assess the association betwee

Question

A 5-year prospective cohort study was conducted to assess the association between cigarette smoking and reduced lung function among 2,561 individuals at-risk. Of these, 493 were followed for 1 year, 562 were followed for 2 years, 437 were followed for 3 years, 622 were followed for 4 years, and 447 were followed for 5 years. By the end of the study, 351 participants had been diagnosed with reduced lung function during the 5-year period. Calculate the incidence density rate per 1,000 person-years. Please give your answer rounded to the 10th decimal place.

Explanation / Answer

Total person-years in the study = sum of number of persons mulitplied by the years of study

= 493 * 1 + 562 * 2 + 437 * 3 + 622 * 4 + 447 * 5 = 7651 person-years

Incidence density rate per person-year = (351/7651)

Incidence density rate per 1000 person-year = (351/7651) * 1000 = 45.8763560319

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