PAFILE= person anchor file

The PFILE= from one run can be used unedited as the person anchor file, PAFILE=, of another.

The person parameter values (thetas) can be anchored (fixed) using PAFILE=. Person anchoring can also facilitate test form equating. The persons common to two test forms can be anchored at the values for one form. Then the measures constructed from the second form will be equated to the measures of the first form. Other measures are estimated in the frame of reference defined by the anchor values.

In order to anchor persons, a data file must be created of the following form:

1. Use one line per person (or person range) to be anchored.

2. Type the sequence number of the person in the current analysis, a blank, and the measure-value at which to anchor the person (in logits if USCALE=1, or in your user-rescaled units otherwise).

               Further values in each line are ignored. An IFILE= works well as an IAFILE=.

3. If the same person appears more than once, the first anchor value is used.

Examples:

2        3.47        ; anchors person 2 at 3.47 logits (or USCALE= values)

10-13        1.3        ; persons 10, 11, 12, 13 are each anchored at 1.3 logits

2        5.2        ; person 2 is already anchored. This person anchoring is ignored

1-50        0        ; all the unanchored persons in the range 1-50 are anchored at 0.

Anything after ";" is treated as a comment.

PAFILE = filename

       Person anchor information is in a file containing lines of format

               person entry number       anchor value

               person entry number       anchor value

PAFILE=*

       Person anchor information is in the control file in the format

               PAFILE=*

               person entry number     anchor value

               person entry number     anchor value

               *

PAFILE=$SnnEnn        or        PAFILE=$SnnWnn

Person anchor information is in the person data records using the column selection rules, e.g., starting in column Snn and ending in column Enn or of width Wnn.        Blanks of non-numeric values indicate no anchor value. PAFILE=$S10E12 or PAFILE=$S10W2 means anchor information starts in column 10 and ends in column 12 of the person's data record (not person label). This can be expanded, e.g, PAFILE = $S23W1+"."+$S25W2 places the columns next to each other (not added to each other)

Example:        The third person in the test is to be anchored at 1.5 logits, and the eighth at -2.7.

1. Create a file named, say, "PERSON.ANC"

2. Enter the line "3 1.5" into this file, meaning "person 3 is fixed at 1.5 logits".

3. Enter the line "8 -2.7", meaning "person 8 is fixed at -2.7 logits".

4. Specify, in the control file,

       PAFILE=PERSON.ANC

       CONVERGE=L                ; only logit change is used for convergence

       LCONV=0.005                ; logit change too small to appear on any report.

or, enter directly into the control file

       PAFILE=*

       3 1.5

       8 -2.7

       *

       CONVERGE=L                ; only logit change is used for convergence

       LCONV=0.005                ; logit change too small to appear on any report.

or, include the anchor information in the data record

       PAFILE=$S1E4

           NAME1=5

           ITEM1=11

       NI=12

       CONVERGE=L                ; only logit change is used for convergence

       LCONV=0.005                ; logit change too small to appear on any report.

       &END

       .....

       END LABELS

   Fred  111010111001        ; this is the first data line

   Mary  011010111100

1.5 Jose  101001111010        ; this data line has an PAFILE= anchor value

   Jo    111110011101

etc.

To check: "A" after the measure means "anchored"

+----------------------------------------------------------------------------------------+

|ENTRY    RAW                        |   INFIT  |  OUTFIT  |PTMEA|        |              |

|NUMBER  SCORE  COUNT  MEASURE  ERROR|MNSQ  ZSTD|MNSQ  ZSTD|CORR.|DISPLACE| PERSONS      |

|------------------------------------+----------+----------+-----+--------+--------------|

|     3     32     35     1.5A    .05| .80   -.3| .32    .6|  .53|     .40| Jose         |