What does the term "mortality" refer to in the context of internal validity?

The term "mortality" in the context of internal validity specifically refers to the loss of subjects between pretest and posttest phases of a study. This can occur for a variety of reasons, such as participants dropping out of the study, moving away, or becoming uncontactable. The significance of mortality lies in its potential to create bias and compromise the study's findings; if certain types of participants are more likely to drop out, the results may not accurately represent the entire population, leading to skewed conclusions.

Maintaining a stable participant group throughout the research process is essential for ensuring reliable and valid results. In studies where attrition is high, the characteristics of the remaining subjects may differ from those of the original group, which can impact the findings and their generalizability. Thus, understanding and controlling for mortality is critical for maintaining internal validity in research.