Hello, I am trying to perform a fit.contrast() on a lme object with this code: attach(error_DB) model_temperature <- lme(Error ~ Temperature, data = error_DB,random=~1|ID) summary(model_temperature) fit.contrast(model_temperature, "Temperature", c(-1,1), conf.int=0.95 ) detach(error_DB) but I got this error Error in `contrasts<-`(`*tmp*`, value = c(-0.5, 0.5)) : contrasts apply only to factors My database is a dataframe, very similar to that of the Orthodont. Could anyone give me some advise on how to solve the problem? Best, Dani -- Daniel Valverde Saub? Grup de Biologia Molecular de Llevats Facultat de Veterin?ria de la Universitat Aut?noma de Barcelona Edifici V, Campus UAB 08193 Cerdanyola del Vall?s- SPAIN Centro de Investigaci?n Biom?dica en Red en Bioingenier?a, Biomateriales y Nanomedicina (CIBER-BBN) Grup d'Aplicacions Biom?diques de la RMN Facultat de Bioci?ncies Universitat Aut?noma de Barcelona Edifici Cs, Campus UAB 08193 Cerdanyola del Vall?s- SPAIN +34 93 5814126