Hi all I am not an experienced user of R. I am trying to perform DIF analysis using Lordif and I get the follow error:
> GroupDIF <- lordif(resp.data=Resp, group=Group, criterion="R2", > pseudo.R2="McFadden", R2.change=0.02) Iteration: 500, Log-Lik: -137340.437, Max-Change: 0.00119 EM cycles terminated after 500 iterations. (mirt) | Iteration: 1, 14 items flagged for DIF (22,25,34,60,64,71,73,75,81,82,83,86,94,95) Iteration: 500, Log-Lik: -131933.514, Max-Change: 0.00033 EM cycles terminated after 500 iterations. ERROR: The following items had negative slope parameters. 87,89,91,93,95,99ERROR: The following items had negative slope parameters (87,89,91,93,95,99). Error in probgrm(theta, DISC[i], CB[i, ]) : slope is missing or negative Does anlyone knows what the poblem might be? Any help is appreciated! Best regards Caroline [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.