This dilemma is known as an ascertainment bias.

Specifically, it arises when there is an ascertainment bias inherent in a study design.

Some regard these studies as exhibiting ascertainment bias which created an impression that Jews are more susceptible to genetic disease than other populations.

Weinberg is also credited as the first to explain the effect of ascertainment bias on observations in genetics.

The result is a form of ascertainment bias.

There is, however, a possibility that ascertainment bias could be the reason that foreign travel was found to be a significant risk factor in our study.

Based on your reference to "ascertainment bias," I assume you are involved in the sciences.

In the process, he recognized that ascertainment bias was affecting many of his calculations, and he produced methods to correct for it.

He discovered the answer to several seeming paradoxes caused by ascertainment bias.

Medical sources sometimes refer to sampling bias as ascertainment bias.