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In the Fit measure group, select C.
The Plot window displays the following graph:
Figure 22-6: Scree plot for C
In this scree plot, the point with coordinate 17 on the horizontal axis has coordinate
64.271 on the vertical axis. This represents the fact that the best 17-parameter model
( ) fits better than the best 16-parameter model ( ), with the
difference being . Similarly, the height of the graph at 18
parameters shows the improvement in C obtained by moving from the best 17-
parameter model to the best 18-parameter model, and so on. The point located above
21 on the horizontal axis requires a separate explanation. There is no 20-parameter
model with which the best 21-parameter model can be compared. (Actually, there is
only one 21-parameter model—the saturated model.) The best 21-parameter model
( ) is therefore compared to the best 19-parameter model ( ). The
height of the 21-parameter point is calculated as . That is, the
improvement in C obtained by moving from the 19-parameter model to the 21-
parameter model is expressed as the amount of reduction in C per parameter.
C 3.071=
C 67.342=
67.342 3.071 64.271=–
C 0=
C 2.761=
2.761 0–()2⁄