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I am trying to do an LRSM Rasch analysis of 72-item data. This data has 67 binary items and 5 ternary items. I need to create a "design matrix" in order to analyze this data. I do not really know what a design matrix is, nor do I know how to create one for my data. Could someone please give me some clues on getting started?

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    $\begingroup$ A design matrix is also called a model matrix. Follow the links to find hundreds of posts about them. $\endgroup$
    – whuber
    Commented Apr 15, 2016 at 15:23

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Design matrix groups all your variables together, typically for regressions. If a variable is categorical, it'll be coded.

You can use model.matrix in R to construct one. However, you shouldn't need to do it yourself because whatever analysis you'll be using should automatically do it for you.

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    $\begingroup$ Thank you very much! That tells me a lot. It turns out I was having trouble due to using an improper analysis. So, I really did not need to construct one. $\endgroup$
    – Fortilto
    Commented Aug 23, 2017 at 16:05

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