| Log linear analysis is an
extention of the chi-square test of independence. In
other words, it considers the situation where you have
more than two nominal independent variables and need to
test whether there is a relationship between them. The printout you receive for a log
linear analysis is similar to that of an ANOVA, but the
interpretation differs somewhat. The test of the A effect
is essentially a goodness of fit for that particular
variable. A significant A effect would mean that the
proportions of cases in each category are not equal on
that variable. What would be a significant interaction
for an ANOVA (such as AC), would mean in a log linear
analysis that a relationship exists between A and C. This
is really analogous to a main effect for A, since one
variable acts as if it were a dependent variable. By the
same logic, a significant ABC effect in log linear
demonstrates a significant relationship between A and B
on the nominal dependent variable C.
When testing effects in
log linear analysis, the goal is to reduce the number of
significant effects that it takes to explain the data.
Thus, the log linear analysis is not finished until it
reaches non-significance for the level of effect you are
testing. For example, test ABC first. If it is
significant, all effects are necessary to explain the
relationships between variables. If it is not
significant, test all lower level effects. In the end,
the equation should contain only those effects which have
been found to be significant (or necessary components of
significant effects).
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