Attrition Effects

Authors
Affiliations

Doctor of Physical Therapy

B.S. in Kinesiology

Doctor of Physical Therapy

B.A. in Neuroscience

Attrition refers to the loss of participants in a study. Attrition effects refers to a type of systematic error and associated bias that arises from systematic differences in the way participants are lost from a study1.

Note

Random attrition overall results in a reduction in overall data for analysis, which will not result in attrition effects1.

Note

A differential loss of pts from one group to another d/t reasons that might impact treatment outcomes such as poor motivation or adverse treatment effects. -Dr. Monroe

Monroe stated this, but I am unsure how this can cause poor motivation if the patients are blinded.

Determining Significant Attrition

Schulz and Grimes Attrition Bias Guide1
Loss to follow-up Study Impact
\(\leq 5\%\) Unlikely to introduce bias1
\(5-20\%\) Might be a source of bias
\(20\%\) Concerning possibility of bias

Although this quick guide is useful, one should also distinguish between overall attrition rates and whether those without follow-up data are different from those with data1.

Prevention

An intention-to-treat analysis should be used to mitigate attrition effects.

References

1.
Nunan D, Aronson J, Bankhead C. Catalogue of bias: Attrition bias. BMJ evidence-based medicine. 2018;23(1):21-22. doi:10.1136/ebmed-2017-110883

Citation

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