Table 8.1 Item infit fit plots

(controlled by FRANGE=, MRANGE=, MTICK=, LOCAL=, MNSQ=, OUTFIT=)

 

These tables are plots of the t standardized fit statistics, INFIT or OUTFIT, against the parameter estimates. INFIT is a t standardized information-weighted mean square statistic, which is more sensitive to unexpected behavior affecting responses to items near the person's measure level. OUTFIT is a t standardized outlier-sensitive mean square fit statistic, more sensitive to unexpected behavior by persons on items far from the person's measure level. The standardization is approximate. Its success depends on the distribution of persons and items. Consequently, the vertical axis is only a guide and should not be interpreted too rigidly. The NORMAL= variable controls the standardization method used.

 

Letters on the plot indicate the misfitting person or items. Numbers indicate non-extreme fit or multiple references. The letters appear on Tables 6, 17, 18, 19 for persons, and Tables 10, 13, 14, 15 for items.

 

Use MNSQ= to change the y-axis to mean-squares.

 

       -4     -3     -2     -1      0      1      2      3      4      5     

      |-----------------------------------------------------------------|      

    5 |                             |     B                             |  5

      |                             |  A                                |     

I   4 |                             |                                   |  4

T     |                             |                                   |     

E   3 |                    C        |                                   |  3

M     |                       D    I|                                   |     

    2 |--------------------------F-G|--Q-M-------------U----------------|  2

I     |                    E       H|                                   |     

N   1 |                            J|T                                  |  1

F     |                      R      |1S       11  1      1   1          |     

I   0 |------------------K-----1----|1-Z1-21-1--1--12-----------------W-|  0

T     |                        O    2 L1    1 x   y  1          1       |     

   -1 |                            1N t22  lnp  r  u       1            | -1

      |                             |vVh     j i     o                  |     

S  -2 |-----------------------------|-w--eg--f----k---------------------| -2

T     |                             | b     d                           |     

D  -3 |                             | a      c                          | -3

      |-----------------------------------------------------------------|     

       -4     -3     -2     -1      0      1      2      3      4      5     

                                  ITEM MEASURE                             

            

PERSON 1   1   2   2    2    3     2       5     4    1    2

        T            S             M            S            T

%TILE  0      10       20   30    60      80    90        99               

 

The person distribution and person percentiles are shown beneath the plot.