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FACTORS AFFECTING EXTERNAL VALIDITY 157

normally distributed population, in which case, the issue of statistical regression
contaminating the experiment does not arise.

Mortality. Since members dropped out of two experimental groups, the effects
of mortality could affect internal validity.
In effect, three of the seven threats to internal validity do apply in this case.
The history, testing, and mortality effects are of concern and hence the internal
validity will not be high.

INTERNAL VALIDITY IN CASE STUDIES

If there are several threats to internal validity even in a tightly controlled lab
experiment, it should become quite clear why we cannot draw conclusions
about causal relationships from case studies that describe the events that
occurred during a particular time. Unless a well-designed experimental study,
randomly assigning members to experimental and control groups and success-
fully manipulating the treatment, indicates possible causal relationships, it would
be impossible to say which factor causes another. For instance, there are several
causes attributed to “Slice,” the soft drink introduced by Pepsico Inc., not taking
off after its initial success. Among the reasons given are (1) a cutback in adver-
tisement for Slice, (2) operating on the mistaken premise that the juice content
in Slice would appeal to health-conscious buyers, (3) Pepsico’s attempts to milk
the brand too quickly, (4) several strategic errors made by Pepsico, (5) underes-
timation of the time taken to build a brand, and the like. While all the above
could provide the basis for developing a theoretical framework for explaining the
variance in the sales of a product such as Slice, conclusions about cause-and-
effect relationships cannot be determined from anecdotal events.

FACTORS AFFECTING EXTERNAL VALIDITY

Whereas internal validity raises questions about whether it is the treatment
alone or some additional extraneous factor that causes the effects, external
validity raises issues about the generalizability of the findings to other settings.
For instance, the extent to which the experimental situation differs from the set-
ting to which the findings are to be generalized is directly related to the degree
of threat it poses to external validity. To illustrate, subjects in a lab experiment
might be given a pretest and a posttest. Those findings, however, cannot be
generalized to the organizational world, where a pretest followed up by a
posttest is rarely administered to employees. Thus the effects of the treatment
will not be the same in the field, and external validity suffers a diminution.
Another threat is the selection of the subjects. In a lab setting, the types of sub-
jects selected for the experiment could be very different from the types of
employees recruited by the organizations. For example, students in a univer-
sity might be allotted a task that could be manipulated to study the effects on
their performance. The findings from this experiment cannot be generalized,