Example: Bias - Study of Spermicide Use and Down Syndrome

Lead Author(s): Jeff Martin, MD

Analysis of Spermicide Use and Down Syndrome Data

We are looking at the effect of spermicide use and the development of Down Syndrome.

Crude and Adjusted Estimates

Here the crude estimate is 3.5

What Should We Report?

What should we report as our final answer, the crude or the adjusted estimate? Before you answer note the decreased precision in the adjusted estimate compared to the crude estimate, as seen in the confidence interval.

Decreased Precision

If you start adding in adjustment of other potential confounders, then you might start to nudge the 95% CI down to 1.

How Sure Are You that Age Is a Confounder?

Your answer should be guided in just how sure you are that age is a confounder. If you are uncertain, then it may not be worth taking the statistical penalty.