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Each point in this graph represents a model for which C is less than or equal to that of
any other model that has the same number of parameters. The graph shows that the best
16-parameter model has , the best 17-parameter model has ,
and so on. While
Best fit is selected, the table of fit measures shows the best model for
each number of parameters. This table appeared earlier on p. 332.
Notice that the best model for a fixed number of parameters does not depend on the
choice of fit measure. For example, Model 7 is the best 17-parameter model according
to C – df, and also according to C / df and every other fit measure. This short list of best
models is guaranteed to contain the overall best model, no matter which fit measure is
used as the criterion for model selection.
You can view the short list at any time by clicking . The best-fit graph suggests
the choice of 17 as the correct number of parameters on the heuristic grounds that it is
the point of diminishing returns. That is, increasing the number of parameters from 16
to 17 buys a comparatively large improvement in C ( ), while
increasing the number of parameters beyond 17 yields relatively small improvements.
Viewing the Best-Fit Graph for Other Fit Measures
E While Best fit is selected, try selecting the other choices in the Fit measure group:
C – df, AIC, BCC, BIC, and C / df. For example, if you click BIC, you will see this:
C 67.342=
C 3.071=
67.342 3.071– 64.271=