Table 2.4 Andrich thresholds (structure calibrations)

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

 

Table 2 for multiple-choice items.

Table 2 for polytomous items.

 

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.

 

Andrich Thresholds (Rasch model parameters: equal-adjacent-probability structure measures) (ILLUSTRATED BY AN OBSERVED CATEGORY)

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

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

|                                                  d    |   55  al07  newspaper

|                                                 c     |   64  sa01  magazine

 

---

 

Polytomous items

 

Table 2.4 shows the Rasch structure calibrations which are the Rasch-Andrich thresholds, also called 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.  There are always one less thresholds than categories. In Table 2.4, "1" is the Andrich threshold between categories 0 and 1. "2" is the Andrich threshold between categories 1 and 2.

 

 

Andrich Thresholds (Rasch model parameters: equal-adjacent-probability structure measures) (ILLUSTRATED BY AN OBSERVED CATEGORY)

-6       -4        -2         0         2         4         6

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

|                                     1       2             |    5  FIND BOTTLES AND CANS

|                                                           |

|                                    1       2              |   23  WATCH A RAT

|         1        2                                        |   18  GO ON PICNIC

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

-6       -4        -2         0         2         4         6

 

                               1

                      12 2 2117083563422342 111 1 1   1     1  KID

                     T      S      M      S     T

                      0    10 30 50 70 80 90               99  PERCENTILE