I got a question about how to deal with my variables for my uni project. I am doing a multiple regression and I got an independent and a dependent variable (both interval scale). To make my model better I control on several confounder variables and one of them is firm size (measured: 1, 2-5, 6-50, 51 or more employees). So basically this means it is on an ordinal scale and hence I learned I would need to make it as a dummy variable, which in return only allows statements compared to the base level and not about my independent variable and which creates a lot of variables to my model. Is it possible/allowed to use this variable (firm size) just as an interval scaled variable or a better way of dealing with this variable?
Thank you so much for your help!
Best Katharina and Michael