and blood pressure is biased because the instrument measures two different
theoretical concepts. Therefore, the researcher would be unable to determine
whether changes in blood pressure were a result of anger or depression. When
appraising an article for threats to construct validity, it is important for readers
to consider information presented in the methods section of the article. This
section should contain information on the reliability of the instrument used
and details on how the validity of the instrument was established.
Confounding means there is a possible error in interpretation of the results
(Cook & Campbell, 1979). This can occur when experimental controls do not allow
the researcher to eliminate possible alternative explanations for the relationship
between the IV (cause variable) and the DV (effect variable). Subject reactivity
and experimenter reactivity are two examples of unintentional confounding.
Subject reactivity means that sometimes subjects are influenced by partici-
pating in a study. Changes noted in the DV can be a result of subject reactivity
and not a result of the IV. This is known as the Hawthorne effect. The Hawthorne
effect was first recognized in studies done at the Western Electric Corporation’s
Hawthorne plant (Mayo, 1933). One of the studies attempted to determine whether
changing the amount of lighting (IV) in the work environment changed worker
productivity (DV). In this study, productivity increased regardless of changes made
to lighting. Thus, one explanation was that increased lighting caused increased
productivity as was hypothesized, but that interpretation did not explain why
productivity increased in the control group. An alternative explanation for this
result was that the increased productivity occurred not because of changes in illu-
mination but because the employees in both groups knew they were being studied.
Therefore, the effect of the IV on the DV was confounded by the subjects’ behavior.
The behavior of subjects in a study may be affected by their personal values, their
desires to please the experimenter or provide the results the experimenter wants,
and congruence of the study with subjects’ personal interests and goals.
Experimenter reactivity is another type of reactivity that threatens external
validity. When researchers have expected or desired outcomes in mind, they
may inadvertently affect how interventions are conducted and how they interact
with subjects. For example, a researcher may be friendlier to subjects in the
experimental group than to subjects in the control group. As a result, subjects in
the experimental group may perceive involvement in the study more positively
than do subjects in the control group.
Have you ever participated in a research study? Do you think your behaviors were different
because you knew you were being studied?CRITICAL THINKING EXERCISE 6-2
KEY TERMS
reactivity: The
influence of
participating
in a study on
the responses
of subjects;
Hawthorne effect
Hawthorne effect:
Subjects’ behaviors
may be affected by
personal values or
desires to please
the experimenter;
reactivity6.2 What Is Validity? 159