Dear friends,

I would like to analyze the effect of a policy on the number of patents using the Diff-in-Diff identification strategy. Firm FE are added to see how the same firm's patenting activities change from before to after the policy. I would also like to control for the registration type of the firm---prior research shows that firms of different registration types (foreign-invested, state-owned, etc.) can differ fundamentally In their decision making and, in my sample, sometimes a firm changes registration type over time, e.g., changes from stated-owned to foreign-invested.

My question is: Does adding registration FE (in addition to firm FE) mean that the same firm is treated as two separate firms, each under a unique registration type? Is this the right way of understanding?

Thank you so much!