Dear r-help members I am a newby to R and would like to estimate a simple boxcox model, e.g. (y^t - 1)/t ~ b0 + b1 * x1 + b2 * x2 unfortunately, R returns with an error message when I try to perform this with the call nls( (y^t - 1)/t ~ b0 + b1 * x1 + b2 * x2, start = c(t=1,b0=1,b1=0,b2=0), data = mydataframe) The error message is Object "t" not found Apparently R seems not to accept parameters on the left hand side of a regression model. I know that the do-it-yourself strategy is not necessary, since the package box-cox is available. Unfortunately, I want the use the box-cox transformation in a quantile regression, i.e. I have to replace nls by nlrq in the call above. Any suggestions? Thanks and best regards, Johannes Ludsteck <><><><><><><><><><><><> Johannes Ludsteck Economics Department University of Regensburg Universitaetsstrasse 31 93053 Regensburg Phone +49/0941/943-2741