Just as there are different interpretations of probability, leading to
different kinds of inferential statements and different conclusions a
bout statistical models and questions, so there are different theories
of measurement, which in turn may lead to different kinds of statisti
cal model and possibly different conclusions. This has led to much con
fusion and a long running debate about when different classes of stati
stical methods may legitimately be applied. This paper outlines the ma
jor theories of measurement and their relationships and describes the
different kinds of models and hypotheses which may be formulated withi
n each theory. One general conclusion is that the domains of applicabi
lity of the two major theories are typically different, and it is this
which helps apparent contradictions to be avoided in most practical a
pplications.