[R] help with the nested anova formulas

[Ben Bolker]

Robert Lynch <robert.b.lynch <at> gmail.com> writes:

>  I am modeling grade as a function of membership in
>  various cohorts.  There
> are four "cohorts".  (NONE, ISE07,ISE08,ISE09) and two times of cohorts
> coded as ISE = TRUE (ISE0#) or FALSE (NONE).  There is clear co-linearity
> but that is to be expected.
> 
>  running the following code
> 
>  CutOff <-0
>  fit.base <- lme(fixed= zGrade ~ Rep + COHORT/ISE + P7APrior + Female +
> White + HSGPA + MATH + AP_TOTAL + Years + EOP + Course,
>                  random= ~1|SID,
>                  data = share[share$GRADE >= CutOff,])
> 
>  I get the following error
> 
>  Error in MEEM(object, conLin, control$niterEM) :
>    Singularity in backsolve at level 0, block 1
> 
>  but if I take out the /ISE I get no error, simmilarly if I take out the
> COHORT/.
> 
>  I want to test for the effects of the different cohorts within the ISE
> subset and across ISE & NONE
> 
> I can send the data (the whole is too large) if you wish.

  Please send this to r-sig-mixed-models at r-project.org for more
discussion.

  The short answer is that lme can't fit models with rank-deficient
fixed effect model matrices -- in other words, there are redundant
parameters in your model because COHORT and ISE between them use
6 parameters to model 4 independent quantities.

http://stats.stackexchange.com/questions/35071/
  what-is-rank-deficiency-and-how-to-deal-with-it