On Thu, Aug 7, 2014 at 10:13 AM, Zofia Ecaterina Taranu <
zofia.taranu@gmail.com> wrote:

> Hi All,
>
> I have a very basic question about the lme4 package and glmer model
> convergence:
>
> Is there a threshold for tolPwrss after which results are no longer
> reliable? I noticed a post online indicating that increasing tolPwrss to
> 0.01 or 0.1 might inflate fixed effect coefficients. On a related, how can
> one detect when coefficient inflation has occurred?
>
> Any suggestions on reference material to read further on this subject
> would be greatly appreciated!
>
> Thank you very much in advance,
>
> Zofia Taranu
>

  It's been quite a  while since I did any experimenting with the tolPwrss
settings -- recent versions (e.g. in the past year or so) have been
sufficiently stable that I haven't needed to mess with the tolPwrss
settings.  If you do, it sounds like you've got a fairly unstable problem
-- have you looked at the data for outliers, weird data, etc.?  Have you
tried with other optimizers (e.g.
https://github.com/lme4/lme4/blob/master/misc/issues/allFit.R ) ?

http://www.math.mcmaster.ca/bolker/R/misc/NM_tolpwrss_vs_deviance.pdf
shows one example of the effects of using different tolerances (I think on
the standard cbpp example included with the package -- I could dig out the
code) -- but this is from a very old version of lme4, don't know what it
would look like if re-done with the current version.

The only real way to know that something bad has happened (as far as I
know) is to test with simulations, i.e. in cases where you know the true
answer.

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