In educational research, mortality (also referred to as experimental mortality or attrition) is a metaphorical term that is used to describe the loss of participants from a study prior to completion. Mortality is among one of eight common threats to internal validity. Threats to validity can be troublesome for research, as these threats limit the conclusions that can be drawn from a study.

Threats to internal validity inhibit researchers’ confidence in reporting that a relationship exists between an independent variable and a dependent variable. To make valid conclusions about the results obtained from a research study, there must be sufficient evidence to substantiate the claim. Mortality threatens this assumption because it compromises the quality and quantity of data garnered from a study.

Mortality is particularly problematic for ...