How to understand the ODS output table ItemInfoCurve in PROC IRT ?

[karlbang]

When I specify

ods output IRT.ItemInfo.ItemInfoCurve=II;

the output data set seems to be stacked (~100 lines per item), but with no indication about which item provides which values ?

[Rick_SAS · Accepted solution]

You are correct: that output is unclear and difficult to work with.

By looking at the output data, you can see that each curve is represented by 101 points. Therefore if you create a new variable PlotNum=ceil(_N_/101), you will correctly identify the curves.

Here is an example that uses the data in the Getting Started example in the PROC IRT documentation:

proc irt data=IrtBinary plots(unpack)=IIC;
   var item1-item10;
   ods output ItemInfoCurve=II_0;
run;

data II;
set II_0;
PlotNum = ceil(_N_ / 101);
run;

proc sgpanel data=II;
   panelby PlotNum / columns=3 rows=2;
   series x=Trait y=ItemInfo;
run;