Hello all, I have just started using fitting the PCM (Partial Credit Model) using eRm and have 2 problems which I cannot solve, I have checked everywhere on the net, but no joy: Firstly, I have fit a PCM model to 10 variables with differing response categories (3 for the first 6 items, 4 for the following 2 and 2 for the last two items). mat1 <- matrix(c(rasch_bart$bart_bowel, rasch_bart$bart_blad, rasch_bart$bart_toil, rasch_bart$bart_feed, rasch_bart$bart_dress, rasch_bart$bart_stairs, rasch_bart$bart_trans, rasch_bart$bart_mob, rasch_bart$bart_groom, rasch_bart$bart_bath), nrow=100, ncol=10) bart_pcm <- PCM(mat1) summary(bart_pcm)
# Item location map plotPImap(bart_pcm, item.subset=c(1,2)) but I can't get the person-item plot to work. I receive an error from R saying: Error in xb[, dim(xb)[2]] : incorrect number of dimensions. Secondly, How would you interpret the following parameter estimates i.e. the eta and beta estimates?: > summary(bart_pcm) Results of PCM estimation: Call: PCM(X = mat1) Conditional log-likelihood: -206.1496 Number of iterations: 40 Number of parameters: 19 Basic Parameters (eta) with 0.95 CI: Estimate Std. Error lower CI upper CI eta 1 0.786 0.565 -0.320 1.893 eta 2 -0.440 0.480 -1.382 0.501 eta 3 -0.709 0.565 -1.817 0.399 eta 4 -0.547 0.428 -1.387 0.292 eta 5 -2.161 0.596 -3.330 -0.992 eta 6 5.036 0.674 3.715 6.358 eta 7 4.250 0.692 2.894 5.606 eta 8 -0.813 0.410 -1.615 -0.010 eta 9 -3.735 0.657 -5.023 -2.447 eta 10 -0.727 0.397 -1.506 0.051 eta 11 -4.671 0.709 -6.061 -3.281 eta 12 -2.417 0.463 -3.324 -1.510 eta 13 3.750 0.585 2.604 4.897 eta 14 2.499 0.613 1.297 3.700 eta 15 -0.589 0.707 -1.975 0.797 eta 16 1.637 0.515 0.627 2.647 eta 17 2.164 0.561 1.065 3.264 eta 18 -0.062 0.656 -1.347 1.223 eta 19 -2.989 0.494 -3.959 -2.020 Item Parameters (beta) with 0.95 CI: Estimate Std. Error lower CI upper CI beta I1.c1 -0.262 0.560 -1.360 0.835 beta I1.c2 0.786 0.565 -0.320 1.893 beta I2.c1 -0.440 0.480 -1.382 0.501 beta I2.c2 -0.709 0.565 -1.817 0.399 beta I3.c1 -0.547 0.428 -1.387 0.292 beta I3.c2 -2.161 0.596 -3.330 -0.992 beta I4.c1 5.036 0.674 3.715 6.358 beta I4.c2 4.250 0.692 2.894 5.606 beta I5.c1 -0.813 0.410 -1.615 -0.010 beta I5.c2 -3.735 0.657 -5.023 -2.447 beta I6.c1 -0.727 0.397 -1.506 0.051 beta I6.c2 -4.671 0.709 -6.061 -3.281 beta I7.c1 -2.417 0.463 -3.324 -1.510 beta I8.c1 3.750 0.585 2.604 4.897 beta I8.c2 2.499 0.613 1.297 3.700 beta I8.c3 -0.589 0.707 -1.975 0.797 beta I9.c1 1.637 0.515 0.627 2.647 beta I9.c2 2.164 0.561 1.065 3.264 beta I9.c3 -0.062 0.656 -1.347 1.223 beta I10.c1 -2.989 0.494 -3.959 -2.020 Thank you in advance for any help which is much appreciated. Michael _________________________________________________________________ Tell us your greatest, weirdest and funniest Hotmail stories ______________________________________________ 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.