One facet must be non-centered in most analyses.

 

This specifies which facets are not to be centered. Other facets are centered, unless they are anchored. Centered facets are constrained to have a mean element measure of zero for non-extreme measures. In most analyses, if more than one facet is non-centered, the frame of reference is not sufficiently constrained and ambiguity results. The usual convention is to center the frame of reference on the agents of measurement: items, tasks, judges. This establishes the origin. Then the objects of measurement, persons, are positioned with respect to this origin.

 

Extreme measures (corresponding to minimum and maximum possible scores) are included in the Means in Table 7, so that these may not be 0 for centered facets.

 

If both Noncenter= and Center= are specified, only the first encountered is actioned.

 

When any element within a facet is anchored, or group anchored, then the origin of the scale for that facet is set by the anchoring. Both Center= and Non-center= are ignored.

 

Example 1: Persons are facet 2 and are not to be centered, then

Noncenter=2

 

Example 2: Facet 1 contains the boys, and facet 3 the girls:

Noncenter=1,3

 

Example 3: All facets are anchored or centered or self-defined:

Noncenter= or Noncenter=0

 

Self-definition occurs when there is only one active facet so that the item difficulties are defined relative to an implicit origin, as in the "Three Mile" example.