I'm using the fwdmsa package to identify deviant cases in a Mokken scale analysis. I've run into a problem. When I use scales comprising a few items, iI tend to get an error: Error in y[order(res[-msamp])][1:(length(samp) + 1 - length(msamp))] : only 0's may be mixed with negative subscripts
I understand that the error is triggered when the algorithm is fetching cases to enter into the next step of the forward search. I don't understand what I can do to remedy this error. The data are dichotomized (1,0) respsonses from a multiple-choice exam that 150 students have completed. If I run the entire test (37 items) , the fwd.msa algorithm works fine. However, the entire test is not unidimensional, so I want to perform separate analyses with the several unidimensional scales comprised by the entire test. Yet when I select those 4-5 item scales, I run into this error. Any ideas how to proceed? The data are 150 responses to a 37 item test. For the first 15 items, they look like this (the variable names are cumbersome and so have been removed) : > head(by364.data) 1 1 1 1 0 1 0 1 1 0 1 0 1 1 1 1 2 1 1 1 0 1 1 1 1 1 1 0 0 1 1 1 3 0 1 1 1 0 0 1 0 1 1 1 0 1 1 0 4 1 1 1 0 0 1 1 1 1 1 1 1 0 1 1 5 1 1 1 1 0 1 0 1 1 1 1 0 1 1 0 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 When I run the fwd.MSA(by364.data) on the full data set "works" fine. However, with shorter (for reasons of unidimensionality) scales, I continuously run into the error above. Any suggestions? Robert -- View this message in context: http://r.789695.n4.nabble.com/small-scales-in-fwdmsa-tp4493479p4493479.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.