Select by clicking on "Test Information" or from the Graphs menu. This shows the Fisher information for the test (set of items) on each point along the latent variable. The test information function reports the "statistical information" in the data corresponding to each score or measure on the complete test. Since the standard error of the Rasch person measure (in logits) is 1/square-root (information), the units of test information would be in inverse-square-logits. See also TCCFILE= and Table 20.
In practice, the values of the information function are largely ignored, and only its shape is considered.
We usually want the test information function to peak
1. where the most important cut-point is (criterion-referenced tests)
2. where the mode of the sample is (norm-referenced tests)
The width of the information function is the effective measurement range of the test.
Buttons are described in Graph window.
To increase the maximum possible Measure range, set EXTREMESCORE=.01 or other small value.
