Ascertainment Bias
Case ascertainment (surveillance) bias
This happens when there is more intense surveillance/ screening for the outcome among exposed than among unexposed.
Example: let's assume that the objective of a case-control study is to assess if a history of past trauma is a risk factor for AS (ankylosing spondylitis). Cases of AS are compared with a random sample of the general population with regard to a history of past trauma. Having a history of trauma, which increases the likelihood of having X-ray investigations, will lead to a higher likelihood of a diagnosis of AS in persons with this trauma history than in the general population. Therefore the proportion of AS cases with a history of past trauma is higher among cases, and the related odds ratio (OR) will be overestimated.
FEM PAGE CONTRIBUTORS 2007
- Contributor
- Arnold Bosman
Root > Assessing the burden of disease and risk assessment > Field Epidemiology > Measurement in Field Epidemiology > Problems with Measurement > Bias > Selection Bias > Selection bias and case-control studies
