Category 2: Generalizing Across Features of a Study
In addition to the fact that each research study is conducted with a specific
group of individuals, the results of a study are demonstrated with a specific
set of procedures. Another question of external validity is, “To what extent
can the results of the study be generalized to other procedures for conducting
the study?”
1. Novelty effect: Participating in a research study is a novel, often exciting
or anxiety-provoking experience for most individuals. In this novel
situation, individuals may perceive and respond differently than they
would in the normal, real world. This is called the novelty effect. In
addition, the treatment(s) administered are typically clearly defined and
unusually salient to the participants. Thus, the behavior (scores) of
individuals participating in a research study may be quite different from
behavior (scores) they would produce in other, more routine, situations
in everyday life.
2. Multiple treatment interference: When individuals are tested in a series
of treatment conditions, participation in one condition may have an
effect on the participants that carries over into the next treatment and
influences their performance or behavior. Common examples are fatigue
and practice effects. With fatigue, participants become tired in one
condition, which causes their performance to deteriorate in the following
treatment. With practice, participants gain experience in one condition
that leads to improved performance in the following condition. In