Difference between revisions of "Ascertainment Bias"
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| + | =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. | ||
[[Category:Selection bias and case-control studies]] | [[Category:Selection bias and case-control studies]] | ||
Revision as of 13:41, 12 April 2023
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.
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
