Hi,

I have data of rainfall for each state and year, and I am explaining it based on the size of the state (just an example). I am running

water_(state,year) = constant + \beta * size + error

I want to introduce year fixed effects, in which case I type

reg water size i.year

The previous line works fine. However, when I want to interact the variable size with the year fixed effects, typing:

reg water size i.year size#i.year

I get the following error:

factor variables may not contain noninteger values

Is there an easy way to get rid of the error, or should I just multiply the variable size with each dummy for each year?