[R] parsing an lmer error with interaction term

From: Brian Riordan <bwriordan_at_gmail.com>
Date: Mon, 14 May 2007 09:57:05 -0400

I'm trying to specify a model using lmer with a binary response and interaction term, but I get an error I can't parse (see below).

Here is some sample data:

Subject Concord Age Disc
SVC999MX148SU-F yes u int
TOU999JU030S1 yes u int
TOU999JU030S1 yes u int
TOU999JU030S1 yes u int
TUT578MX037S2 yes g int
COL140MX114S2 yes yf mix
COL140MX114S6 yes u mix
COL140MX114S2 yes yf mix

COL425MX075S2 yes of mix
COL425MX075S2 yes of mix
COL425MX075S2 yes of mix
STP560JG118S14 no g pnl
STP560JG118S22 no g pnl
STP560JG118S20 no g pnl
STP560JG118S15 no g pnl
STP560JG118S20 no g int

And here is the model:

lmer_int_ageXdisc <- lmer(Concord ~ Age*Disc

    + (1|Subject), family="binomial", data=d, method="Laplace")

In the actual data set the AgexDisc interaction should have 16 levels.

This produces the error:

Error in devLaplace(PQLpars) : Leading minor of order 7 in downdated X'X is not positive definite

What does this mean? This error is not thrown for other interactions I specify from my data.

Here is my session info:

R version 2.4.1 (2006-12-18)

LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] "stats" "graphics" "grDevices" "utils" "datasets" "methods"
[7] "base"

other attached packages:

       lme4 Matrix lattice
"0.9975-13" "0.9975-11" "0.14-17"

Thanks in advance for your help!

Brian Riordan
NICHD Postdoctoral Fellow
Psychological and Brain Sciences
Indiana University

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