Detection bias refers to systematic differences between groups of a study in how the outcome is assessed, while performance bias is introduced by unequal care between groups and has nothing to do with how the outcome is assessed.
In other words, detection bias occurs when the patient’s characteristics influence the probability of detecting the outcome and performance bias occurs when the researchers provide unequal care between groups or when patients in different groups behave differently in a way that can affect the outcome.
Similarities between detection bias and performance bias
Both detection and performance bias can alter the study results unpredictably (i.e. they can either overestimate or underestimate the effect of the treatment on the outcome).
And both can be avoided by using a blinding (or better, a double blinding) approach. For detection bias, participants and outcome assessors (especially when dealing with subjective outcomes) should be blinded. For performance bias, participants and clinicians who provide the treatment should be blinded.
Example of detection bias
Suppose we are interested in examining the hypothesis that: “Parents who were abused as children are more likely to abuse their own children”. The problem is that parents who were abused as children are more involved with a child protection service agency and this makes them more likely than other parents to be reported if they abuse their own children, which may introduce detection bias. [Source]
Example of performance bias
In 2014, a qualitative study was conducted to examine the reaction of overweight participants on being randomized to either:
- receive over 12 months of weight loss training done by experts (treatment group)
- or receive the usual care provided by general practitioners (control group)
Participants in the control group were disappointed for being offered usual care instead of the new helpful program, so the researchers concluded that their reaction to disappointment may introduce performance bias. [Source]