Last observation carried forward (LOCF) is a method of imputing missing data in longitudinal studies. If a person drops out of a study before it ends, then his or her last observed score on the dependent variable is used for all subsequent (i.e., missing) observation points. LOCF is used to maintain the sample size and to reduce the bias caused by the attrition of participants in a study. This entry examines the rationale for, problems associated with, and alternative to LOCF.


When participants drop out of longitudinal studies (i.e., ones that collect data at two or more time points), two different problems are introduced. First, the sample size of the study is reduced, which might decrease the power of the study, that is, its ability to ...

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