For one famous epidemiologic study, physicians were given a questionnaire about

Question

For one famous epidemiologic study, physicians were given a questionnaire about their tobacco smoking habits at the start of the study (November 1951), and the occurrence of lung cancer in these physicians was documented over a 10 year period (November 1951 through October 1961) (Doll&Hill, 1964). The following table shows numbers of lung cancer deaths by the end of the study (Oct 1961) by daily number of cigarettes smoked at the time of the 1951 questionnaire. Person-years of observation are given for each smoking category. Compute the mortality rates and rate ratios for each category of smoking, using non-smokers as the referent group

2.A. (8 pts)+ Deaths Mortality rate Daily number from lung Rate per 1000 of cigarettes cancer s at risk person-years Ratio o 42,800 O.07 1 38,60o 22 15-24 54 38,900 25 57 25,100 All smokers 133 102,600 Total 136 145,400 2.B. (2 pts) Interpret one of the rate ratios you calculated in 3.A.

Explanation / Answer

Mortality rate calculation

eg: 3*1000/42800 = 0.07

Rate ratio calculation = 0.57/0.07 = 8.1

b) The results could be interpreted to mean that mortality rates increase with the number of cigarettes a person uses daily.

Rate ratio of 8.1 indicates mortalit rate increase by 8 times fold with reference year.

Daily no if cigarettes Deaths Person -years at risk Mortality rate Rate ratio 0 3 42800 0.07 1 1 to 14 22 38600 0.57 8.1 15-24 54 38900 1.39 19.8 25+ 57 25100 2.25 32.4 all smokers 133 102600 1.3 18.6 Total` 136 145400

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