I'm undertaking Rasch analysis, using Winsteps, on two separate scales, using survey data. This is for a conference presentation next month (ACSPRI/RC33 in Sydney), and I hope to eventually publish the results in a journal article. The first scale I am working with is dichotomous true/false data with 14 items. It's going well, apart from I can't work back from the person measure to the expectation for each item (using the output observation file XFILE data). The person measure seems to be very close to the mean of the log(expectation/1-expectation) values for the items for each person, but not exactly the same.
I would love to be able to say which output values can be used to substitute in for the original True/False values to run further analyses, say structural equation modelling or factor analysis, on the results. But these require item-level results for each person and not a total score. Do I just divide the log(expectation/1-expectation) by the number of items to get the score to use for each individual item?
Any comments appreciated. This is just for extension for the audience, and in case I get questions.