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)
i386-pc-mingw32

locale:
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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