Hi Ewen, Let me apologise first, and explain that when I saw your message, I misunderstood, and did not parse it correctly as a question, but simply as someone giving a useful further example of a previous problem. Working through issues in the ZeligMultilevel package is on list of current issues and on the near-horizon, and I had read your message as a useful code example of the issue, rather than a question to move this to the top of the list. I've fixed the immediate issue in the "ls.mixed" model. You can download a revision of ZeligMultilevel with this fix as: install.packages("ZeligMultilevel", repos="http://r.iq.harvard.edu", type="source") And then the following now runs: library(Zelig) library(ZeligMultilevel) z.out<-zelig(Reaction ~ Days + tag(Days|Subject), data=sleepstudy, model="ls.mixed") x.out<-setx(z.out, Days=4.4) x1.out<-setx(z.out, Days=6.6) s.out<-sim(z.out, x=x.out, x1=x1.out) s2.out<-sim(z.out, x=x.out) We are currently building a package for Panel data, and in the course of that, reevaluating what exactly the various quantities of interest are in Panel and Multilevel models, with group level indicators, and how it might be best to change setx() or sim() to allow building more specific or precisely controlled quantities of interest. If people have thoughts, please feel free to comment on or off list. Also, as we update the quantities of interest for ZeligMultilevel, we'll change and improve the related plot abilities, and so any ideas there are great too. Thanks again for the code example that illuminated the problem in this model, James. -- James Honaker, Senior Research Scientist //// Institute for Quantitative Social Science, Harvard University ________________________________________ From: zelig-bounces(a)lists.gking.harvard.edu [zelig-bounces(a)lists.gking.harvard.edu] on behalf of Ewen Harrison [mail(a)ewenharrison.com] Sent: Thursday, May 16, 2013 4:10 AM To: zelig(a)lists.gking.harvard.edu Subject: Re: [zelig] Persistent mixed models error Ewen Harrison <ewen.harrison@...> writes: whether a fix was found. The error is replicated using the sleepstudy data included in lme4. z.out<-zelig(Reaction ~ Days + tag(Days|Subject), data=sleepstudy, model="ls.mixed") in array(x, c(length(x), 1L), if (!is.null(names(x))) list(names(x), : attempt to set an attribute on NULL Pity not to get any response to this. I've had a lot of difficulties with Zelig 4 which are all resolved by going back to Zelig 3.5. For anyone finding this thread, it's straightforward: Download this: http://cran.r-project.org/src/contrib/Archive/Zelig/Zelig_3.5.5.tar.gz Run this: install.packages("C:/*YOUR PATH*/Zelig_3.5.5.tar.gz", repos = NULL, type="source") Best wishes, Ewen - -- Zelig Mailing List, served by HUIT Send messages: zelig(a)lists.gking.harvard.edu [un]subscribe Options: http://lists.gking.harvard.edu/mailman/listinfo/zelig Zelig program information: http://gking.harvard.edu/zelig/ Zelig mailing list Zelig(a)lists.gking.harvard.edu To unsubscribe from this list or get other information: https://lists.gking.harvard.edu/mailman/listinfo/zelig