Facet control characters

Control characters can be difficult to understand at first. On first reading, skip down to the sections on "Examples" and "Matching" to get the feel of what this is all about.

Facets are positioned in the same order in the Model= specification as they are positioned in the data lines. Each model definition includes one entry for each facet in a data line. Zero terms, "0", in the Entry= specification are bypassed.

Model= Facet control characters	Meaning for this facet

?	Model can match a datum with any element number in this facet, e.g., any examinee.

#	Model can match a datum with any element number in this facet, e.g., any item. Also, each element of this facet matched to this model has its own rating scale, i.e., "#" specifies a "partial credit" model.

blank	Ignore this facet when matching the Model= statement to a datum, but verify that the element number for this facet for a datum that matches this model statement is listed after Labels=. Typed as ",,".

X	Ignore this facet when matching data to this Model= statement. Do not check for the element number in this facet for validity when a match occurs.

0	Model can only match a datum in which this facet does not participate, i.e., when element number 0 is used for this facet in the datum reference.

- e.g., -? or -#	Reverses the orientation of the measure of the element of facet, when combined with other facet control characters. "-?" means can match any element, but with the element's measure reversed in direction and sign. When using -?, it is recommended that the data be entered twice, once with each facet as -?, and the Models= be weighted 0.5.

an element number, e.g., 23	Model can only match a datum with exactly this element number in this facet.

number-number, e.g., 23-36	Model can match a datum with any element number from the specified range in this facet.

number#, e.g., 23# or 23-36#	Model can match a datum with a matching element number from the specified number, but each element number is associated with a unique "partial credit" scale.

B, e.g., Model= ?B,?,?B,R	Generate Bias interaction estimates for combinations of the elements of each facet marked by "B". At least two "B" terms are needed. The "B" is appended to one of the other facet control characters, e.g., "?B". The bias interactions are coded in one or more model statements, but act as though they are coded in all model statements. Model statements with different combinations of facets marked by "B" each produce separate sets of bias estimates for all the data.

Example: A test in which every item has a different rating scale (partial credit) with a different numbers of categories. The highest numerical category of any item "6".

Model = ?, ?, #, R6 ; this allows items with categories such as 0,1,2 and also 1,2,3,4,5,6