Can someone please give me an example of how to enter starting values for a GRM (IRT) model using the ltm package? The instructions from the ltm manual are below, but when I create either a list of the values or a matrix I get the error, "start.val not of proper type." I can find no example on the web other than using NULL or Random, which won't work for me. The code I'm using looks something like this: row1 <- c(0.146, 1.505, 2.158) row2 <- c(4.124, 5.790, 1.589) row3 <- c(3.635, 4.916, 1.426) startval_list <- c( row1 , row2 , row3) Results <- grm( DelT4 , constrained = FALSE, start.val = startval_list) ...which produces the error mentioned above. Manual instructions: start.val - a list of starting values or the character string "random" . If a list, each one of its elements corresponds to each item and should contain a numeric vector with initial values for the extremity parameters and discrimination parameter; even if constrained = TRUE the discrimination parameter should be provided for all the items. If "random" random starting values are computed. Thanks Jeff