Hi, I am currently trying to fit a multinomial logit model on my data. I have tried to search for some example, and this is the one that I followed and worked. http://www.ats.ucla.edu/stat/r/dae/mlogit.htm However, I am having difficulties finding out the meaning of the model specified in the following line: mlogit.model<- mlogit(brand~1|female+age, data = mldata, reflevel="1") The main issue is the "|". I found out that it means multi-part formula but I have no idea what it means mathematically in this particular case. Can anyone enlighten me? Many thanks -- View this message in context: http://r.789695.n4.nabble.com/A-basic-question-in-model-formula-specification-tp2526765p2526765.html Sent from the R help mailing list archive at Nabble.com.