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GRFILE= probability curve coordinate output file |
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If GRFILE=filename is specified, a file is output which contains a list of measures (x-axis coordinates) and corresponding expected scores and category probabilities (y-axis coordinates) to enable you to use your own plotting program to produce item-category plots like those in Table 21.
GRFILE=? opens a Browse window
For the numbers plotted for empirical ICCs, see the "Empirical ICC" plot, "Copy data to Clipboard"
These are usually relative to the item difficulty, so
If you want the item information function relative to the item difficulty, use the GRFILE=
If you want the item information function relative to the latent variable, add the item difficulty to the GRFILE= value.
The plotted range is at least MRANGE= away from its center.
This file contains:
1. An example item number from the response-structure grouping (I5) - see ISGROUPS=
2. The measure (F7.2) (user-rescaled by USCALE=)
3. Expected score (F7.2)
4. Statistical information (F7.2)
5. Probability of observing lowest category (F7.2)
6 etc. Probability of observing higher categories (F7.2).
If CSV=Y, values are separated by commas. When CSV=T, values are separated by tab characters.
Example: You wish to write a file on disk called "MYDATA.GR" containing x- and y-coordinates for plotting your own category response curves.
GRFILE=MYDATA.GR
With CSV=Y
"PROBABILITY CURVES FOR LIKING FOR SCIENCE (Wright & Masters p.18) Jul 4 16:03 2000"
;ITEM,MEAS,SCOR,INFO,0,1,2
1,-3.00,.11,.10,.89,.10,.00
1,-2.94,.12,.11,.89,.11,.00
1,-2.88,.12,.11,.88,.12,.00
1,-2.82,.13,.12,.87,.12,.00
1,-2.76,.14,.12,.87,.13,.00
1,-2.70,.14,.13,.86,.14,.00
With CSV=N (fixed spacing)
; PROBABILITY CURVES FOR LIKING FOR SCIENCE (Wright & Masters p.18) Nov 23 23:31 2008
ACT MEAS SCOR INFO 0 1 2
1 -3.00 .11 .10 .89 .10 .00
1 -2.94 .12 .11 .89 .11 .00
1 -2.88 .12 .11 .88 .12 .00
1 -2.82 .13 .12 .87 .12 .00
1 -2.76 .14 .12 .87 .13 .00