There are at least three different kinds of generalization, and each can be
a concern for external validity.
1. Generalization from a sample to the general population. Most research
questions concern a large group of individuals known as a population.
For example, a researcher may be interested in preschool children or
adults with an eating disorder. In each case, the population contains
millions of individuals. However, the actual research study is conducted
with a relatively small group of individuals known as a sample. For
example, a researcher may select a sample of 50 preschool children to
participate in a study. One concern for external validity is that the sample
is representative of the population so that the results obtained for the
sample can be generalized to the entire population. If, for example, a
researcher finds that television violence influences the behavior of
preschool children in a sample, the researcher would like to conclude tha