2.6.2.3. External validity. External validity refers to
the domain to which a study’s findings or presumed
causal relationships may be generalized (Cook and
Campbell, 1979; Kidder and Judd, 1986; Yin, 1989).
Within the overall criticism of lack of rigor, one of
the most serious charges against case-based research
is the claim that the “sample of cases” is normally
too small to allow generalization of the results. If
this criticism were valid, it would severely limit the
usefulness of case-based methods. However, it stems
from a misunderstanding between two types of generalization.
Survey research relies on statistical generalization,
whereas case studies (as with experiments)
rely on analytical generalization (Yin, 1989, p. 43).