Question

Suppose we repeat the case-control study from above to determine if being obese confounds the relationship between blood clots and oral contraceptives. The crude odds ratio is calculated and equals 3.25. You stratify your 2x2 tables by BMI (a BMI > 25 is considered obese; BMI < 24.9 is considered a healthy weight) status and find that the stratum specific odds ratio for individuals who are obese is 3.25, and the stratum specific odds ratio for individuals with a healthy weight is 3.25. Based on these results, we would state the obesity is a(n)

Answer 1

Obesity does not serve as a confounder in the relationship between blood clots and oral contraceptives because the stratum-specific odds ratios remained constant when the data were stratified by BMI.

Step-by-step explanation:

The student's question relates to determining if obesity confounds the relationship between blood clots and oral contraceptives. Given that the crude odds ratio is 3.25, and stratification of the data by BMI has yielded stratum-specific odds ratios of 3.25 for both obese individuals and individuals with a healthy weight, we can conclude that obesity does not act as a confounder in this relationship. This is because a confounding variable would show different associations in stratified analyses, which is not the case here.

In this case, we are investigating whether obesity confounds the relationship between blood clots and oral contraceptives. The crude odds ratio is 3.25, which indicates an increased risk. When stratifying the data by BMI, we find that the stratum-specific odds ratio for both obese individuals and those with a healthy weight is also 3.25. Based on these results, we would state that obesity is a confounding factor in this relationship. This means that obesity is influencing the observed association between blood clots and oral contraceptives.