(controlled by T2SELECT=, MRANGE=, CATREF=)

 

Multiple-choice items

 

Table 2.3 shows the 50% cumulative probability points, the Rasch-Thurstone thresholds. The lower category ("a" and other wrong answers) has a greater than 50% probability of being observed up to 3.2 logits, when "d", the correct answer, has a higher than 50% probability.

 

TABLE 2.3 50% CUMULATIVE PROBABILITY: MEDIAN (ILLUSTRATED BY AN OBSERVED CATEGORY)

-4    -3     -2     -1      0      1      2      3      4

|------+------+------+------+------+------+------+------|  NUM   TOPIC

a                                                  d    d   55  al07  newspaper

a                                                 c     c   64  sa01  magazine

 

Table 2.13 is the same as Table 3, but the options are shown by their scored values, not by their codes in the data.

 

TABLE 2.13 50% CUMULATIVE PROBABILITY: MEDIAN (BY CATEGORY SCORE)

-4    -3     -2     -1      0      1      2      3      4

|------+------+------+------+------+------+------+------|  NUM   TOPIC

0                                                  1    1   55  al07  newspaper

0                                                 1     1   64  sa01  magazine

 

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Polytomous items

 

Tables 2.3 & 2.13: The "Cumulative Probability" Table: Rasch-Thurstone thresholds, selected with CURVES=001, answers the question "whereabouts in the category ordering is a person of a particular measure located?" This information is expressed in terms of median cumulative probabilities (the point at which the probability of scoring in or above the category is .5).

 

                                   CUMULATIVE PROBABILITY: MEDIAN               

               -6        -4        -2         0         2         4         6

                -------------------------------------------------------------                             

 5 FIND BOTTLES 0                                       1          2        2

23 WATCH A RAT  0                                      1          2         2

 9 LEARN WEED N 0                              1          2                 2

21 WATCH BIRD M 0                      1          2                         2

11 FIND WHERE A 0                     1          2                          2

19 GO TO ZOO    0             1          2                                  2

18 GO ON PICNIC 0         1          2                                      2

                -------------------------------------------------------------                             

               -6        -4        -2         0         2         4         6