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FACTORS AFFECTING INTERNAL VALIDITY 151

validity and vice versa. To ensure both types of validity, researchers usually try
first to test the causal relationships in a tightly controlled artificial or lab setting,
and once the relationship has been established, they try to test the causal rela-
tionship in a field experiment. Lab experimental designs in the management area
have thus far been done to assess, among other things, gender differences in
leadership styles, managerial aptitudes, and so on. However, gender differences
and other factors found in the lab settings are frequently not found in field stud-
ies (Osborn & Vicars, 1976). These problems of external validity usually limit the
use of lab experiments in the management area. Field experiments are also infre-
quently undertaken because of the resultant unintended consequences—person-
nel becoming suspicious, rivalries and jealousies being created among
departments, and the like.

FACTORS AFFECTING INTERNAL VALIDITY

Even the best designed lab studies could be influenced by factors that might
affect the internal validity of the lab experiment. That is, some confounding fac-
tors might still be present that could offer rival explanations as to what is caus-
ing the dependent variable. These possible confounding factors pose a threat to
internal validity. The seven major threats to internal validity are the effects of
history, maturation, testing, instrumentation, selection, statistical regression, and
mortality and these are explained below with examples.

History Effects
Certain events or factors that would have an impact on the independent vari-
able–dependent variable relationship might unexpectedly occur while the experi-
ment is in progress, and this history of events would confound the cause-and-effect
relationship between the two variables, thus affecting the internal validity. For
example, let us say that the manager of a Dairy Products Division wants to test
the effects of the “buy one, get one free” sales promotion on the sale of the com-
pany-owned brand of packaged cheese, for a week. She carefully records the
sales of the packaged cheese during the previous 2 weeks to assess the effect of
the promotion. However, on the very day that her sales promotion goes into
effect, the Dairy Farmer’s Association unexpectedly launches a multimedia adver-
tisement on the benefits of consuming dairy products, especially cheese. The
sales of all dairy products, including cheese, go up in all the stores, including the
one where the experiment had been in progress. Here, because of unexpected
advertisement, one cannot be sure how much of the increase in sales of the
packaged cheese in question was due to the sales promotion and how much to
the advertisement of the Dairy Farmers’ Association! The effects of history have
reduced the internal validity or the faith that can be placed on the conclusion
that the sales promotion caused the increase in sales. The history effects in this
case are illustrated in Figure 7.1.
To give another example, let us say a bakery is studying the effects of
adding to its bread a new ingredient that is expected to enrich it and offer