Edit: The subset of the dataframe I provided way giving a different error, so I've replaced the pastebin entry with the full data frame.
Here's the top of the data frame, then read into mlogit format by
clogitdf <- mlogit.data(df1, choice= "y", shape="long", alt.var="id_var")
PriceNorm = Price of brand normalized to size (eg. $/oz.)
Inc = Income
y = (Consumer's choice: Tide, Surf, or Wisk)
Here's the model:
reg2 <- mlogit(y ~ PriceNorm | Inc, data=clogitdf, id.var="id_var", reflevel="surf")
The goal is to model how consumers prefer the three brands Tide, Surf, and Wisk. When I run the model, I get a positive coefficient on
PriceNorm = 13.8. I'm confused because my interpretation of that coefficient is that for a $1/oz. increase in the price of Surf, consumer utility increases by 13.8.
It would help me if you can check my work and make sure the model is doing what I intend it to, so I know whether to trust the PriceNorm coefficient or not.
Edit: I spoke to my professor today, and
PriceNorm should definitely be negative. I think I need to include the dummy variables, but when I do, I get an error saying the model is exactly singular.