CURVES= curves for Tables 2, 21 = 111, all

Interpreting rating (or partial credit) scale structure is an art, and sometimes counter-intuitive. See the examples in RSA.

Table 21 provides three curves for each rating (or partial credit) scale definition. Table 2 provides the equivalent response locations for each item. The first curve shows the probability of response in each category. The second curve shows the expected score ogive. The third curve shows the cumulative probability of response in each category or below. The 50% cumulative probability medians are at the intersections of these curves with the .5 probability line. The control indicators of "1" and "0", in the 1st, 2nd or 3rd position of the CURVES= variable, select or omit output of the corresponding curve.

1??        Probability curves

?1?        Expected score ogives, model inter characteristic curves

??1        Cumulative probability curves, showing .5 probability median category boundaries.

       CURVES=000        indicates no curves are to be drawn - Table 21 will be skipped, unless STEPT3=N, in which case only the structure summaries are output.

       CURVES=111        draw all 3 curves in Table 21 (and 3 versions of Table 2)

       CURVES=001        draw only the 3rd, cumulative probability score, curve.