Environmental Variables: General Threats to Internal Validity
for All Studies
It is possible that variables in the general environment of the study such as size
of room, time of day, or gender of the experimenter can become threats to
internal validity. If one treatment is administered in a large, cheerful room
and another treatment is administered in a small, dreary room, it is possible
that the type of room (and not the treatment) is responsible for any differences
between the scores in the two treatment conditions. Another example of this
type of problem is a taste-test study that compared consumer preference for
Coca-Cola versus Pepsi-Cola. In this study, individuals were asked to taste the
colas in two different glasses and identify the one they preferred. The participants
were not told which cola was in each glass but the glasses were marked