Question

5. Smoking and duodenal ulcers. The Health Professionals Follow-up Study is a prospective study of heart disease and cancer among more than 50,000 health professionals in the United States who were 40–75 years of age in 1986. Every two years questionnaires are sent to these individuals, and newly diagnosed cases of various diseases reported. The following data are constructed from the surveys returned in the 1993 mailing. The investigators in this study were interested in the relationship between smoking status and duodenal ulcers, a common disorder of the gastrointestinal tract. The incidence of duodenal ulcers for the three groups is presented below:

Smoking and the Incidence of Duodenal Ulcers

	Number of Persons at Start of study	Number of Observed New Cases of Duodenal Ulcers
Nonsmokers	22,295	60
Past smokers	20,757	60
Current smokers	4,754	16

Calculate the relative risk of being a past smoker and a current smoker, relative to never having smoked. (Hint: You should make two tables, one for smokers and one for past smokers.)

Answer 1

The relative risk between current smokers and nonsmokers

	Number of Persons at Start of study	Number of Observed New Cases of Duodenal Ulcers	Total
Current smokers	4,754	16	4770
Nonsmokers	22,295	60	22,355
Total	27,049	76

The incidence of exposed is $4754\div \left (4754+16) = 0.996$

The Incidence of non exposed $22,295\div \left (22,295+60) = 0.997$

So, the Relative Risk among current smokers and nonsmokers is

$0.996\div 0.997=0.998$

The risk is almost same for both group

its means there is no significant chance of duodenal ulcer among current smokers than none smokers.

There is no association between current smoking and duodenal ulcer

The relative risk between past smokers and nonsmokers

	Number of Persons at Start of study	Number of Observed New Cases of Duodenal Ulcers	Total
Past smokers	20,757	60	20,817
Nonsmokers	22,295	60	22.355
Total	43,052	120

The incidence of exposed is $20,757\div \left (20,757+60) = 0.997$

The incidence of non exposed is $22,295\div \left (22,295+60) = 0.997$

So, the Relative Risk among past smokers and nonsmokers is

$0.997\div 0.997=1$

the risk is the same for both of group

So, there is no association between Past smoking and duodenal ulcer