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Help desk => Questions and Answers => Topic started by: cucho_veas on November 25, 2019, 06:16:59 PM

Hi. After running a multidimensional Rasch analysis of a 3category scale, the estimates of the step categories are shown with the Table Item Parameter Estimates, but the value of the last step is constrained. Is it possible to free this parameter so that I can see the real value?

No, the constraint of the last step parameter to be the negative sum of the rest is a necessary identification constraint for the model.
An easier way to interpret the rating scale or partial credit model you are estimating would be to look at the Thurstonian Thresholds (e.g., table 7 in the Show: `show ! tables = 1:2:3:4:7;`). In your example of it item scored 0, 1, 2, there will be 2 thresholds, labeled x.1 and x.2 (where x is your item numbers). Each threshold can be interpreted as the location on the latent trait at which the probability of achieving score >= 1 is > 0.5 (x.1) and score >=2 is 0.5 (x.2).

Thank you for the information. I've checked the thresholds correctly.