Question

Calculate the value for the marked cell (?).

Risk of coronary death, by number of cigarettes smoked per day, for 1,416 employed middle-aged men: Chicago Western Electric study, 22-year follow-up.
No. Cigarettes smoked per day	No. at risk	Person-years	No. of coronary deaths over 22 years	Risk per 1000 persons per year (CI)	Risk per 1000 person-years (ID)
0	645	12,757	84	?	?
1-14	197	3,794	33	?	?
15-24	387	7,074	73	?	?
25-60	187	3,244	42	?	?
Total	1416	26,869	232	?	?

Answer 1

Solution :

Given the above table we have to find out the "Risk per 1000 persons per year (CI or Cumulative Incidence)" and "Risk per 1000 person-years (ID or Incidence Density)".

Cumulative Incidence (CI) : CI is defined as the ratio of the Total number of new cases of a disease in a time period and the Total population at risk. Mathematically, we can write,

So the Cumulative Incidence for the differenct number of cigarettes smoked are ,

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Incidence Density (ID) : ID is defined as the ratio of the Total number of new cases of a disease in a time period and the Total person-time of observation. Mathematically, we can write,

So the Incidence Density for the differenct number of cigarettes smoked are ,

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Thus , the final table will be ,

Risk of coronary death, by number of cigarettes smoked per day, for 1416 employed middle-aged men : Chicago Western Electric study, 22 - year follow up.
No.of Cigarettes smoked per day	No. at risk	Person - years	No.of coronary deaths after 22 years	Risk per 1000 person per year (CI)	Risk per 1000 person - years (ID)
0	645	12757	84	5.92	6.58
1-14	197	3794	33	7.61	8.70
15-24	387	7074	73	8.57	10.32
25-60	187	3244	42	10.21	12.95
Total	1416	26869	232	7.45	8.63

The answers are given in the table !!

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