[R-sig-ME] Exponent random effect in nlmer

Cole, Tim tim.cole at ucl.ac.uk
Tue Oct 11 11:29:13 CEST 2016

I have a model of the form
  m1 <- lmer(y ~ f + (1 | id) )
where y is a continuous variable centred on zero, f is a unordered factor with coefficients b such 0 < b < 1, and there is a signficant random subject intercept.

The random intercept can lead to predicted values outside the valid range (0, 1). For this reason I'd like to reformulate the model as
m2 <- nlmer(y ~ (f - 1) ^ exp(1 | id) )   (using a invalid but I hope obvious notation), where the random effect is now a power centred on 1. This would constrain the fitted values to be within c(0, 1).

My question is: can this be done in nlmer, and if so how? Please can someone point me in the right direction?

Tim Cole
Tim.cole at ucl.ac.uk<mailto:Tim.cole at ucl.ac.uk> Phone +44(0)20 7905 2666 Fax +44(0)20 7905 2381
Population, Policy and Practice Programme
UCL Great Ormond Street Institute of Child Health, London WC1N 1EH, UK

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