I have just submitted MiscPsycho to CRAN. MiscPsycho contains functions for miscellaneous psychometrics that may be useful for applied psychometricians. MML estimation already exists in the ltm package. Hence, a jml option is provided for users who prefer this method. The jml function gives back rasch difficulties and the same Infit and Outfit statistics as Winsteps.
Also, jml is known to return biased parameter estimates. So, a correction for jml bias is provided for as an optional argument in the function. Currently, the package includes the following: 1) jml() a function for joint maximum likelihood estimation of the Rasch model 2) alpha() , coefficient alpha 3) alpha.Summary(), gives what alpha would be if item i were excluded 3) scoreCon(), create score conversion tables, 4) class.acc(), classification accuracy statistics 5) simRasch(), simulate Rasch item responses 6) classical(), point-biserial and p-values Future versions will include Master's partial credit model, DIF statistics, procedures for linking scales (e.g., Stocking-Lord), lattice graphics for item characteristic curves, and bayesian scoring methods (EAP). Below is a sample session: set.seed(1) # for replication only xx <- simRasch(200, 10) # Simulate data for 200 persons and 10 items classical(xx$data) # get p-values and point-biserials alpha(xx$data) # coefficient alpha alpha.Summary(xx$data) aa <- jml(xx$data) # estimate item parameters scoreCon(aa$params) The student in row 1 has a number correct score of 3 out of 10. From the score conversion table, his theta estimate is -1.36. So, we can ask, what is the probability that his true score is above, say, .5 on the theta scale. class.acc(as.numeric(xx$d[1,]), aa$params, .5, aboveQ=T) Any recommendations, bugs, hints, comments, are welcome. Harold Doran [[alternative HTML version deleted]] _______________________________________________ R-packages mailing list [EMAIL PROTECTED] https://stat.ethz.ch/mailman/listinfo/r-packages ______________________________________________ R-help@stat.math.ethz.ch 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.