Wash out period:
            a certain fixed time period that must elapse between the subject's first observation and their subsequent observation of the same event.

University of Michigan - Ann Arbor

Recall bias is a error that occurs when participants do not remember previous events or experiences accurately or omit details: the accuracy and volume of memories may be influenced by subsequent events and experiences.

Recall Bias

Catalogue of Bias Collaboration, Nunan D, Bankhead C, Aronson JK. Selection bias. Catalogue Of Bias 2017: [www.catalogofbias.org/biases/selection-bias/](https://www.catalogofbias.org/biases/selection-bias/) 

Catalog of Bias

Recall bias usually occurs in studies which involve self-reporting, such as case-control studies and retrospective cohort studies.

Types of Studies where Recall bias happens

- Can potentially exaggerate the relation between a potential risk factor and the disease.
- Might not remove factors which may not be correalted

Major Problems with recall bias

How to Account for recall bias

A patient being treated for ADHD might remember certain large events in time of panic or neglect small gradual changes

A trial of cancer patients not sharing family history

Example of recall bias

Take Tobacco case as an example, the interviewer must have known whether they had cancer or not, which is likely to affect their recollection. 

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