[R-sig-ME] Logistic modelling with guessing parameter

[Ben Bolker]

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  Quick possibility: PIRLS failures are often a symptom of the
algorithm hitting a non-finite (infinite/NaN) value internally (this
should be better instrumented).  I would try instrumenting your
link/inverse-link/dmu.eta functions to have them warn/stop if they
would be returning a non-finite value ...



On 15-05-07 01:13 PM, Peter Harrison wrote:
> Hello everyone,
> 
> I'm currently modelling response data for a musical error detection
> experiment. Participants' responses can either be correct (1) or
> incorrect (0); the difficulty of the question is predicted by a
> number of factors, including accuracy (accurate performance ->
> errors are difficult to detect) and musical piece ("audio_name").
> 
> The model I'm fitting is similar to a 3-PL IRT model, with a
> constrained guessing parameter of 0.5 (i.e. the most difficult
> questions should be answered with a 50% success rate). However,
> instead of the normal conception of item difficulty, probability of
> correct response is given by a linear combination of
> difficulty-related predictors (such as accuracy and audio_name).
> Therefore:
> 
> probability of correct response = 0.5 + 0.5 / (1 +
> exp(predictors))
> 
> where predictors = e.g. a*accuracy + b*audio_name + c (but with
> audio_name dummy coded, with different b for each level of
> audio_name).
> 
> I've been using a script kindly posted by Ken Knoblauch back in
> 2010
> (https://stat.ethz.ch/pipermail/r-sig-mixed-models/2010q4/004531.html)
> to achieve this using lme4, simply changing a few terms to keep it
> up-to-date with current package versions (see bottom of message for
> the script). It seems to work fine with "accuracy" as a fixed
> effect and "p_ID" as a random effect. However, I want to add
> "audio_name" as a fixed effect, i.e. responses ~ accuracy +
> audio_name + (1|p_ID). But when I do this, I get the following
> error message: (maxstephalfit) PIRLS step-halvings failed to reduce
> deviance in pwrssUpdate.
> 
> I'm not sure what this error message means, but have been assuming
> it is talking about a convergence problem. I've tried various
> things to fix it, including
> control=glmerControl(optimizer="bobyqa"),
> control=glmerControl(optimizer="Nelder_Mead"), and nAgQ=3, but none
> of these have worked.
> 
> Would anyone be able to help me with this error message, and what
> to do about it?
> 
> Thanks so much! Peter
> 
> 
> Key to data file:
> 
> accuracy = accuracy of the music clip (higher accuracy -> question
> is more difficult) = continuous variable audio_name = musical piece
> played = categorical variable (27 levels, coded with text strings) 
> p_ID = participant ID = categorical variable (229 levels, coded
> 1:229) behind_beat = whether clip was behind the beat or not =
> dichotomous (1 = TRUE, 0 = FALSE)
> 
> Script:
> 
> library(lme4) data <-
> read.csv("https://dl.dropboxusercontent.com/s/szq2e2sxwfsuxo6/data.csv",
> header = TRUE)
> 
> mafc.logit <- function (.m = 2) { .m <- as.integer(.m) if (.m < 2) 
> stop(".m must be an integer > 1") linkfun <- function(mu) { mu <-
> pmax(mu, 1/.m + .Machine$double.eps) qlogis((.m * mu - 1)/(.m -
> 1)) } linkinv <- function(eta) { 1/.m + (.m - 1)/.m *
> binomial()$linkinv(eta) } mu.eta <- function(eta) ((.m - 1)/.m) *
> binomial()$mu.eta(eta) valideta <- function(eta) TRUE link <-
> paste("mafc.logit(", .m, ")", sep = "") structure(list(linkfun =
> linkfun, linkinv = linkinv, mu.eta = mu.eta, valideta = valideta,
> name = link), class = "link-glm") }
> 
> mod1 <- glmer(responses ~ accuracy + (1|p_ID), family =
> binomial(mafc.logit(2)), data=data) summary(mod1)
> 
> [[alternative HTML version deleted]]
> 
> _______________________________________________ 
> R-sig-mixed-models at r-project.org mailing list 
> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
> 

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