Selective Attrition in Psychology Experiments

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What Is Selective Attrition?

In psychology experiments, selective attrition describes the tendency of some people to be more likely to drop out of a study than others. This tendency can threaten thevalidityof a psychological experiment.

When data is collected at two or more points in time during an experiment, there will naturally be people who begin a study but then find that they cannot continue. Dropping out of a study can occur for a wide variety of reasons and can occur in both experimental and longitudinal designs.

It is important to note that selective attrition does not mean that certain people are more likely to quit a study. Instead, it simply implies that there is a tendency for people to quit an experiment for a variety of reasons.

Causes of Attrition

The main reasons why people drop out of research studies are sometimes referred to as the four M’s:

Attrition Bias

While selective attrition doesn’t imply that certain types of participants are more likely to drop out of a study, attrition can result in a research bias when the people who prematurely exit a study are fundamentally different from those who remain in the study.

When this happens, researchers end up with a final study group that is quite different from the original sample.

Because of the differences between the original sample and the final group of participants in a study, something known as an attrition bias can affect the results of the study.

Threats to Validity

When certain groups of individuals drop out of a study, attrition can also affect the validity of the results. Since the final group of participants no longer accurately reflects the originalrepresentative sample, the results cannot be generalized to a larger population.

Selective attrition will happen naturally with a study that occurs over such a long period of time. Some participants will move, some will lose interest, some with suffer from illness, and some will even pass away.

But what if certain groups of individuals become more prone to selective attrition? Suppose that widowers tend to drop out of the study more frequently than those who have a surviving spouse. Because the final sample lacks data from this group, it may no longer reflect the tendencies that exist in the overall population at large, threatening the external validity of the study and making it difficult to generalize the results to the entire populace.

Internal validitycan also be a problem with there are different attrition rates between thecontrol groupsand theexperimental groups. If researchers were conducting an experiment on treatment for anxiety, for example, the results of the study might be biased if people in the experimental group dropped out at a higher rate than those in the control group.

Consider, for example, if this attrition rate is due to anxiety that prevents participants from completing the study. Since the experimental group includes a higher proportion of individuals who benefited from the treatment, the results will be biased and suggest that the treatment was perhaps more effective than it really was.

A Word From Verywell

Some attrition is only natural in psychology studies. Very high levels of attrition, however, can hurt the validity of the results. Research has also shown that selective attrition can also impact research results. In one study, for example, researchers found that attrition led to overestimates of the effects of treatment.

4 SourcesVerywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Salthouse TA.Selectivity of Attrition in Longitudinal Studies of Cognitive Functioning.J Gerontol B Psychol Sci Soc Sci. 2014;69(4):567-574. doi:10.1093/geronb/gbt046Nunan D, Aronson J, Bankhead C.Catalogue of bias: Attrition bias.BMJ Evid Based Med. 2018;23(1):21-22. doi:10.1136/ebmed-2017-110883Barry AE.How Attrition Impacts the Internal and External Validity of Longitudinal Research.J Sch Health. 2005;75:267-270. doi:10.1111/j.1746-1561.2005.00035.xKaplan RM, Atkins CJ.Selective attrition causes overestimates of treatment effects in studies of weight loss.Addict Behav. 1987;12(3):297-302. doi:10.1016/0306-4603(87)90044-x

4 Sources

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Salthouse TA.Selectivity of Attrition in Longitudinal Studies of Cognitive Functioning.J Gerontol B Psychol Sci Soc Sci. 2014;69(4):567-574. doi:10.1093/geronb/gbt046Nunan D, Aronson J, Bankhead C.Catalogue of bias: Attrition bias.BMJ Evid Based Med. 2018;23(1):21-22. doi:10.1136/ebmed-2017-110883Barry AE.How Attrition Impacts the Internal and External Validity of Longitudinal Research.J Sch Health. 2005;75:267-270. doi:10.1111/j.1746-1561.2005.00035.xKaplan RM, Atkins CJ.Selective attrition causes overestimates of treatment effects in studies of weight loss.Addict Behav. 1987;12(3):297-302. doi:10.1016/0306-4603(87)90044-x

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Salthouse TA.Selectivity of Attrition in Longitudinal Studies of Cognitive Functioning.J Gerontol B Psychol Sci Soc Sci. 2014;69(4):567-574. doi:10.1093/geronb/gbt046Nunan D, Aronson J, Bankhead C.Catalogue of bias: Attrition bias.BMJ Evid Based Med. 2018;23(1):21-22. doi:10.1136/ebmed-2017-110883Barry AE.How Attrition Impacts the Internal and External Validity of Longitudinal Research.J Sch Health. 2005;75:267-270. doi:10.1111/j.1746-1561.2005.00035.xKaplan RM, Atkins CJ.Selective attrition causes overestimates of treatment effects in studies of weight loss.Addict Behav. 1987;12(3):297-302. doi:10.1016/0306-4603(87)90044-x

Salthouse TA.Selectivity of Attrition in Longitudinal Studies of Cognitive Functioning.J Gerontol B Psychol Sci Soc Sci. 2014;69(4):567-574. doi:10.1093/geronb/gbt046

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

Barry AE.How Attrition Impacts the Internal and External Validity of Longitudinal Research.J Sch Health. 2005;75:267-270. doi:10.1111/j.1746-1561.2005.00035.x

Kaplan RM, Atkins CJ.Selective attrition causes overestimates of treatment effects in studies of weight loss.Addict Behav. 1987;12(3):297-302. doi:10.1016/0306-4603(87)90044-x

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