Table 1.

Definitions of Potential Biases Encountered in the Review

Bias	Definition
Selection bias	When the study population is different from that of the general population or of the population of interest, leading to a systematic error in an association or outcome.16
Recall bias	Systematic error due to differences in accuracy or completeness of recall of memories pertaining to past events or experiences.17
Observer bias	The difference between the actual, true value and the value noted due to observer variation.18
Perception bias	The tendency of observers to be subjective about people and events, causing biased information to be collected in a study or the biased interpretation of the study’s results.19