UIMEAN= or UMEAN= the mean or center of the item difficulties = 0

Assigns your chosen numerical value to the average measure of the non-extreme items (UEXTREME=No) or all items (UEXTREME=Yes), i.e., a criterion-referenced measure. UMEAN= and UIMEAN= are the same specification. The last UIMEAN= or UPMEAN= values in the control file is actioned.

 

UIMEAN= and UPMEAN= are ignored when there are anchor values, IAFILE= or PAFILE=. Anchor values are treated according to UASCALE=

 

Table 20 gives the UMEAN= and USCALE= values for a conversion that gives the measures a range of 0-100.

 

Example 1: You want to recenter the item measures at 10 logits, and so add 10 logits to all reported measures, to avoid reporting negative measures for low achievers:

UIMEAN = 10

 

Example 2: You want to recenter and user-rescale the item measures, so that the range of observable measures goes from 0 to 100.

Look at Table 20.1. Beneath the Table are shown the requisite values, e.g.,

UMEAN = 48.3 ; this is the same as UIMEAN=48.3

USCALE = 9.7

 

For more examples, and how to compute this by hand, see User-friendly rescaling

 

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Rescaling with anchor values:

 

When you do the analysis, you need the anchored values and their scaling:

UASCALE=  anchor values per logit

IAFILE=*

1 20

2 34

...

*

 

Then you have options:

 

A. Use the "Help" menu scaling USCALE= calculator to discover the new values you want:

UIMEAN= new mean

USCALE= new scaling

 

B. If you know the rescaling you want, include in the control file:

TFILE=*

UIMEAN= new mean

USCALE= new scaling

*

 

In both options, use the Output Tables menu or Output Files menu to produce the output you need.