epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evidenc ...

, lagging (or ''exposure lagging'') means excluding the exposure in a time period before registration of an outcome. It may be motivated by that the actual outcome had actually occurred before the registration of it, and that the last exposure before registration did not contribute to the case. For example, when studying

risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often use ...

s of cancer, the cancer process may have been triggered long before actual diagnosis of cancer, and that therefore any exposure to risk factors in the ''lag'' time between may be unimportant. It can be used to mitigate

protopathic bias Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population int ...

, that is, when a treatment for the first symptoms of a disease or other outcome appear to cause the outcome. Protopathic bias is a potential bias when there is a lag time from the first symptoms and start of treatment before actual diagnosis.

References

{{Reflist Epidemiology