Question

On June 30, 2013, investigators recruit 1700 study participants and ask them questions regarding their salt intake history and whether or not they have experienced a heart attack. The investigators then develop a 2x2 which shows that 950 of the subjects were exposed to high salt intake. Of those 950 subjects, 526 of them experienced a heart attack. In total, 676 subjects experienced a heart attack.

A: Identify exposure and health outcome

B. Identify the study type

C. Based on the study type, identify the most appropriate measure of association

D. Construct an appropriate 2x2 table and calculate the most appropriate measure of association

Answer 1

a) Exposure is high salt intake and the health outcome is experiencing a heart attack.

b) The study design is case control study design as we are comparing the two groups - one having history of heart attack and other that didn't had heart attack in past and asking whether they had high salt intake or not. So, it is a restrospective study where we are moving from effect to cause and hence, a case control study.

c) The most effective measure of association which is appropriate here is odds ratio.

If odds ratio = 1 it means no exposure has no effect on outcome.

Odds ratio > 1 means exposure is a risk factor.

Odds ratio < 1 means exposure is a protective factor.

d)

Exposure \Outcome	Had heart attack	did not had heart attack	Total
High salt intake	526 (a)	950 - 526 = 424 (b)	950
Normal salt intake	676 - 526 = 150 (c)	1024 - 424 = 600 (d)	1700 - 950 = 750
Totally	676	1024	N= 1700

Odds ratio is given by -

Since, O.R > 1, we conclude that high salt intake is the risk factor for heart attack.