mortality (in research)

Definition
"Mortality: A threat to internal validity consisting of a loss of research participants between a pretest and posttest stemming from the influence of the treatment itself. Also referred to as attrition. "

• What does "mortality" mean in research design?

"The more serious problem is the systematic loss of subjects who drop out because of a common reaction to the treatment. " (Suter, Ch7. pg 14)