Question

A cohort study evaluating causes of mortality among 20,000 men (aged 40-59) with coronary heart disease was conducted, following men for 2 years. If were smokers at the time of enrollment, they were told of the continued health risks associated with smoking. The number of deaths occurring by the end of the 2-year period among men classified by smoking behavior are given below. Fill in the mortality rate for each group.

	Smoker at baseline and continued smoking through study	Smoker at baseline and quit at baseline (did not smoke during study)	Past smoker at baseline (stayed not smoking in study)	Never smoker
Alive at end of study	4920	1840	3800	7840
Deceased at end of study	1080	2000	4000	8000
Mortality rate (per 1000 per year)

a) What is the rate of excess mortality among smokers (who smoked during the follow-up period) as compared to the never smokers?

b) What is the rate of excess mortality among smokers as compared to the men who quit smoking at baseline?

Answer 1

	Smoker at baseline and continued smoking through study	Smoker at baseline and quit at baseline (did not smoke during study)	Past smoker at baseline (stayed not smoking in study)	Never smoker
Alive at end of study	4920	1840	3800	7840
Deceased at end of study	1080	2000	4000	8000
Mortality rate (per 1000 per year)	(1080/2*(4920+1080))*1000 = 90 per 1000 per year	(2000/2*(1840+2000))*1000 = 260 per 1000 per year	(4000/2*(4000+3800))*1000 = 256 per 1000 per year	(8000/2*(7840+8000))*1000 = 253 per 1000 per year

Formula used to calculate mortality rate (per 1000 per year) in above table is =

(# deceased / (# participated in study*# years))*1000

# participated in study = (#deceased + #Alive) at end of the study

1. Rate of excess mortality among smokers is 90 per 1000 per year as compared to the never smokers which is 253 per 1000 per year.
2. Rate of excess mortality among smokers is 90 per 1000 per year as compared to the men who quit at baseline is 260 per 1000 per year.

Thank you for the question. The questions a and b are bit confusing. I have answered as much I understood. If you have any doubt please ask in comment section.