Hi Herv?, thanks for your answer, you are right, package is drc on CRAN, and this is its reference manual: http://cran.r-project.org/web/packages/drc/drc.pdf Further searches returned the package ic50 (http://cran.r-project.org/web/packages/ic50/) as more appropriate for this analysis, just in case for next users. Sorry for my late reply 'cause of holidays, thanks you again, Andrea Citando Hervé Pagès <hpages at="" fhcrc.org="">: > On 11-08-10 02:04 AM, andrea.grilli at ior.it wrote: >> Hi to all, >> I have 4 cell lines, 2 in group A and 2 in group B, for which I >> calculated IC50. >> I want to know if there is some difference between the 2 groups: a >> simple t-test seems to me a not correct test for this case. Do you know if exists in DRC package (or in any other package) a more specific test and how to perform it? > > I don't know anything about those tests but just wanted to mention that there is no DRC package in Bioconductor (there is a drc pkg on CRAN though...) > >> I checked in manual but I didn't find a solution. > > It would probably be helpful to know which manual you checked exactly. > > Cheers, > H. > >> >> Thanks in advance, >> Andrea