At the end of a three-year study, Lene finds that 12 percent of her participants did not take part in the final survey because they moved away to another city. In research terms, Lene is experiencing issues related to _____.

A) maturation
B) testing
C) regression
D) mortality

Mortality refers to the loss of participants during the course of a study, and in this case, Lene's loss of participants is due to them moving away from the area, which is a form of mortality. Maturation refers to changes in participants over time, testing refers to the effects of repeatedly taking a test, and regression refers to the tendency for extreme scores to move closer to the mean on subsequent testing.