﻿ UPMEAN= the mean or center of the person abilities

# 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

Item Easiness = Reversed Item Difficulties

The reversal formula for the items on the maps in Tables 1.10, 1.11, 1.12, 1.13, 12.12, and 16.13 is:

Item Easiness = 2*Mean Person Ability - Item Difficulty

For  a full set of item easiness statistics, set the Mean Person Ability as the reference point, then reverse the user-scaling:

For the person ability statistics:

UEXTREME = Yes

UPMEAN = 0 or preferred reference value

USCALE = current value of USCALE=

For the matching item easiness statistics:

UEXTREME = Yes

UPMEAN = 0 or preferred reference value

USCALE = - current value of USCALE=

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Rating Scale Analysis, Wright & Masters Introduction to Rasch Measurement, E. Smith & R. Smith Introduction to Many-Facet Rasch Measurement, Thomas Eckes Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments, George Engelhard, Jr. & Stefanie Wind Statistical Analyses for Language Testers, Rita Green
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