Dear Sir/Madam,

I am interested in the scaling procedure of WLE scores of PISA 2015 databases. The descriptions about how to compute WLE scores from the PISA 2015 technical report are listed below:

"For the regular scales, international item and person parameters were obtained from a GPCM (see formula 16.3) in a single analysis based on data from all persons in all countries using the mdltm software (von Davier, 2008). For each scale, only persons with a minimum number of three valid responses were included. Students were weighted using the final student weight (W_FSTUWT), and all countries contributed equally to the estimation. Additional analyses on the invariance of item parameters across countries and languages were conducted and unique parameters were assigned if necessary (see section “Cross-country comparability” in this chapter). Once this process was finished, weighted likelihood estimates (WLE; Warm, 1989) were used as individual participant scores and transformed to an international metric with an OECD mean of zero and an OECD standard deviation of one."

I tried to use Stata 14.2 to compute the WLE scores but can't work successfully.
What the command I used are:

irt gpcm varlists [weight=w_fstuwt]


The results are like the picture below. But the "Discrim value" from the results are not the same as the data in PISA technical report(showed as the second picture below).
Can anyone help me? What's wrong with it? And how to get the WLE scores at next step by following with this procedure?
May I use the command "predict" ?

Thank you very much for help.

Sincerely,
Doris


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