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

 

Multiple-choice items

 

Table 2.4 shows the item difficulties (or more generally the Rasch-Andrich thresholds) coded by the option of the higher category. For item "al07" this is "d", the correct option.

 

TABLE 2.4 STRUCTURE MEASURES (Rasch model parameters: equal-adjacent-probability thresholds) (ILLUSTRATED BY AN OBSERVED CATEGORY)

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

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

|                                                  d    |   55  al07  newspaper

|                                                 c     |   64  sa01  magazine

 

Table 2.14 is the same as Table 4, the Rasch-Andrich thresholds, but the options are shown by their scored values, not by their codes in the data.

 

TABLE 2.14 STRUCTURE MEASURES (Rasch model parameters: equal-adjacent-probability thresholds) (BY CATEGORY SCORE)

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

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

|                                                  1    |   55  al07  newspaper

|                                                 1     |   64  sa01  magazine

 

---

 

Polytomous items

 

Tables 2.4 & 2.14 show Rasch structure calibrations: Rasch-Andrich thresholds (step parameters, step measures, step difficulties, rating (or partial credit) scale calibrations). These are the relationships between adjacent categories, and correspond to the points where adjacent category probability curves cross, i.e., are equally probable of being observed according to a Rasch model.

 

STRUCTURE MEASURES (Rasch Parameters)

-40 -30   -20   -10     0    10    20    30    40    50

|-----+-----+-----+-----+-----+-----+-----+-----+-----|  NUM   ACT

|                                 1      2            |    5  FIND BOTTLES AND CANS

|        1                  2                         |    1  WATCH BIRDS

|               2    1                                |   13  GROW GARDEN

|                                                     |

|                2                                    |   12  GO TO MUSEUM

|                                                     |

|      1                2                             |   11  FIND WHERE ANIMAL LIVES

|                                                     |

|        1         2                                  |   10  LISTEN TO BIRD SING

|                                                     |

|                                                     |

|        1  2                                         |   19  GO TO ZOO

|      2      1                                       |   18  GO ON PICNIC

|-----+-----+-----+-----+-----+-----+-----+-----+-----|  NUM   ACT

-40 -30   -20   -10     0    10    20    30    40    50