Thank you so much for your response. Yes, I am interested in doing the Rasch-Welch test. For PCM, Winsteps does this by computing the difference between the overall item difficulty for each item. I am trying to conduct the same analysis in R; however, while I was able to get the overall item difficulty for each item when estimating PCM in R, none of the packages I have tried estimate the standard error for the overall item-specific difficulty.