epidemiological Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and Risk factor (epidemiology), determinants of health and disease conditions in a defined population, and application of this knowledge to prevent dise ...

research, recall bias is a

systematic error Observational error (or measurement error) is the difference between a measurement, measured value of a physical quantity, quantity and its unknown true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. Such errors are ...

caused by differences in the accuracy or completeness of the

recollection Recall in memory refers to the mental process of retrieving information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial r ...

s retrieved ("recalled") by study participants regarding events or experiences from the past. It is sometimes also referred to as response bias, responder bias or reporting bias.

Explanation

Recall bias is a type of measurement bias, and can be a

methodological In its most common sense, methodology is the study of research methods. However, the term can also refer to the methods themselves or to the philosophical discussion of associated background assumptions. A method is a structured procedure for bri ...

issue in research involving

interview An interview is a structured conversation where one participant asks questions, and the other provides answers.Merriam Webster DictionaryInterview Dictionary definition, Retrieved February 16, 2016 In common parlance, the word "interview" re ...

s or

questionnaire A questionnaire is a research instrument that consists of a set of questions (or other types of prompts) for the purpose of gathering information from respondents through survey or statistical study. A research questionnaire is typically a mix of ...

s. In this case, it could lead to misclassification of various types of exposure. Recall bias is of particular concern in

retrospective A retrospective (from Latin ', "look back"), generally, is a look back at events that took place, or works that were produced, in the past. As a noun, ''retrospective'' has specific meanings in software development, popular culture, and the arts. ...

studies that use a case-control design to investigate the

etiology Etiology (; alternatively spelled aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek word ''()'', meaning "giving a reason for" (). More completely, etiology is the study of the causes, origins ...

of a disease or psychiatric condition. For example, in studies of risk factors for

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

, women who have had the disease may search their memories more thoroughly than members of the unaffected control group for possible causes of their cancer. Those in the case group (those with breast cancer) may be able to recall a greater number of potential risk factors they had been exposed to than those in the control group (women unaffected by breast cancer). This can potentially exaggerate the relation between a potential risk factor and the disease.

Prevention

To minimize recall bias, some clinical trials have adopted a "wash out period", i.e., a substantial time period that must elapse between the subject's first observation and their subsequent observation of the same event. Use of hospital records rather than patient experience can also help to avoid recall bias. Standardising sampling methods can help to avoid needing recall information in the first place. Often, recall bias is difficult to avoid, and many studies change experiment design to avoid recalling information.

References

{{Biases Cognitive biases Sampling (statistics)