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In a hypothetical case-control study of 200 cases of heart disease and 260 unmatched controls, the...

In a hypothetical case-control study of 200 cases of heart disease and 260 unmatched controls, the following 2x2 table was determined for the association of sedentary lifestyle with heart disease:

	Cases	Controls
Sedentary lifestyle	140	70
Not sedentary lifestyle	60	190
	200	260

(a) Compute the odds ratio for sedentary lifestyle and heart disease.

(b) There is concern that sex may be a confounder in the relationship between sedentary lifestyle and heart disease. What three conditions must be true for sex to be a confounder in this study?

Females:

	Cases	Controls
Sedentary lifestyle	20	60
Not sedentary lifestyle	20	180
	40	240

Males:

	Cases	Controls
Sedentary lifestyle	120	10
Not sedentary lifestyle	40	10
	160	20

(d) Does the relationship between sedentary lifestyle and heart disease appear to differ for females and males? (That is, is there an interaction between sex, sedentary lifestyle, and heart disease?) Why or why not?

(e) Does sex confound the relationship between sedentary lifestyle and heart disease seen in part (a) above? Why or why not?

Solutions

Expert Solution

(a)

Answer- odds in sedentary life style = 140/70

= 2

Odds in non sedentary life style = 60/170

= 0.3529

Final odd ratio = odds in sedentary lifestyle/ odds in non sedentary lifestyle

= 2/ 0.3529

= 5.667

(b) Answer - For sex to act as a confounder three following conditions could be true -

1. Low physical activity such as not doing exercise at all can also lead to heart disease.
2. High alcohol consumption .
3. Smoker.

Odds in sedentary lifestyle = 120/10

= 12

Odds in non sedentary lifestyle = 40/10

= 4

Final odd ratio = 12/4

= 3

Females -

odds in sedentary lifestyle = 20/60

= 0.333

odds in non sedentary lifestyle = 20/180

= 0.111

Final odd ratio = 0.333/ 0.111

= 3

(d) No the relationship between sedentary lifestyle and heart disease not appear to differ for females and males as their final odd ratio comes to equal which means that either males or females living in sedentary lifestyle as equal outcome to heart diseases

(e) No sex confound the relationship between sedentary lifestyle and heart disease cannot be seen in part (a) above. As in table of part (a) no separate information about Male and female is given we cannot confound sex.

Nightingale answered 1 year ago

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