PROC IRT True Score Curve

[wadams]

Hi Everyone,

Does anyone have good coding resources for outputting a true score curve from PROC IRT results?

Thank you,

Bill

[ballardw]

You might provide, as a minimum, the code you are using to create your IRT model so have some idea what your results might look like.

I am not familiar with the term 'True Score Curve' in this context. Can you provide a link to the definition you are using?

[wadams]

Hi ballardw - I have not written any syntax for this analysis yet.  I am deciding on using PROC IRT or IRTPRO.  As an example, if I used PROC IRT to score a five-item examination and, for individuals with an ability of 1.17, the results show that the probability of a correct response to item 1 = 0.99, to item 2 = 0.93, to item 3 = 0.89, to item 4 = 0.78, and to item 5 = 0.74, then I know their expected true score on the original score scale should simply be the sum of these probabilities or 0.99 + 0.93 + 0.89 + 0.78 + 0.74 = 4.33.  That is how I am defining "true score" here (though I know it often called a trait score as well). 

So, ultimately, I want the true (or trait) score on the y-axis and latent trait on the x-axis (sort of like the attached Figure from the RJ de Ayala IRT textbook).  Thank you!

Bill