UPMEAN = the mean or center of the person abilities = (computed)

Assigns your chosen numerical value to the average of the non-extreme abilities for persons  (UEXTREME=No) or all  persons(UEXTREME=Yes), i.e., this provides a norm-referenced user-scaling.

 

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=

 

Example 1: You want to used conventional IRT norm-referenced user-scaling with person mean of 0 and person S.D. of 1.

UPMEAN = 0

USCALE = 1 / (person S.D. in logits) ; find this from Table 3.1

If there are extreme person scores, see User-friendly rescaling

 

Example 2: I want to compare the mean performance of random samples of examinees from my database. Will UPMEAN= help in this?

 

UPMEAN=0 sets the local mean of the persons to zero (excluding extreme scores) regardless of the sampling.

If you wish to investigate the behavior of the person mean for different person samples, then

(1) analyze all persons and items: set UPMEAN=0, for convenience, and write IFILE=. For better comparison, set STBIAS=NO.

(2) anchor the items using IAFILE=

(3) analyze samples of persons with the anchored items.

The person means reported in Table 3.1 now show person means (with or without extreme scores) in the one frame of reference across all analyses defined by the anchored items.

 

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