Bortfall

Bortfall is a Swedish noun that denotes loss, disappearance, or failure to occur in a given context. In statistical and research contexts, bortfall refers to data that are missing or observations that are not available for analysis. This can result from nonresponse, withdrawal of participants, dropouts, or data recording problems. Bortfall can be classified as unit bortfall (the entire observation is missing) or item bortfall (specific data points are missing within a case).

In research, bortfall may bias results and reduce statistical power, especially if the missingness is related to the studied outcome. Analysts distinguish mechanisms such as missing completely at random, missing at random, and not missing at random, and choose methods accordingly. Common approaches include complete-case analysis, single or multiple imputation, and weighting or model-based techniques that account for missing data. The choice of method depends on the presumed mechanism of bortfall and the study design.

Outside statistics, bortfall is also used to describe dropout in education or training programs and loss to follow-up in clinical studies. In such contexts, bortfall is a practical concern for evaluating program effectiveness and ensuring representativeness of results.

Etymology: bortfall is formed from the prefix bort- (away) and fall (an occurrence or fall), reflecting the sense of something that has fallen away or failed to occur. See also missing data, attrition, nonresponse, dropout.