What refers to the impact on study results when subjects differ significantly in their initial characteristics?

The impact on study results when subjects differ significantly in their initial characteristics is referred to as statistical regression. This phenomenon occurs when individuals with extreme values on a particular measure are naturally expected to move closer to the mean when measured again, thus affecting the outcomes of a study.

In research, if participants begin with varying baseline characteristics, particularly extreme scores, there’s a tendency for their subsequent measurements to converge toward the average. This can lead to misleading conclusions if the changes are interpreted as effects from an intervention when, in fact, they may simply reflect this regression toward the mean.

In contrast, other concepts like mortality refer to participant dropout rates, manipulation relates to the deliberate alteration of variables in an experiment, and maturation involves changes within subjects over time that may impact their responses. Each of these factors does play a role in research dynamics, but they do not capture the idea of how the initial differences among subjects can skew results as effectively as statistical regression does.