I am trying to run a regression model where the Y is concentration and predictors are stove type (e.g., stove1, stove 2, stove 3) and fuel type (e.g., wood, crop waste, LPG). Stove 3 uses only the fuel type LPG, while Stove 1 and Stove 2 use wood and crop waste. When conducting the multiple linear regression, the fuel type LPG gives me a coefficient of "NA" (I am using R statistical software). I am not really clear as to why this is coming up as NA, other than to say something along the lines of because Stove 3 only uses 1 fuel type, LPG, it is returning NA for the regression results. Is this an example of collinearity and if not what is it and can I still use the regression model as I have set it up?
Thanks.
Thanks.