Example: Selection Bias - Loss to Follow-Up - AIDS

Lead Author(s): Jeff Martin, MD

Losses to follow-up are a grave problem in AIDS studies.

Progression to AIDS

Consider a cohort study looking at progression to AIDS (as shown in the Kaplan-Meier curves below), This is pertinent because there has been a lot of interest in whether the way you got HIV (parenterally or via sex) influences your initial inoculum of virus (and host immune response) and ultimately your disease course.

Setting for Selection Bias

In a study like this, all the ingredients are present for selection bias, the perfect storm.

More IDU Lost to Follow-Up

Assume also that injection drug users (IDU) are more likely to become lost to follow up at any given level of feeling sick because of less social support and more chaotic lives.

Kaplan-Meier Curve

Thus, this is what a Kaplan-Meier curve would look like.


Schematic for Loss to Follow-Up

You can see effect of selection bias schematically in the diagram below.