Hi everyone, I am trying to estimate the production function for manufacturing firms in India and I have a lot of 0 investments. I want to use an intermediate input as a proxy but I also want to control for the selection bias. I know that I can use -levpet- to use intermediate input as a proxy but does LP (20030 and -levpet- control for self-selection as well? LP don't discuss selection in their paper so I was wondering if the selection part from OP is still valid. Some resources on the internet suggest that it does, but I am not sure whether the model or the command -levpet- do so. You help will be greatly appreciated. Thanks!