The screenshot below is from a paper that I am reading and the author says it is a non-parametric regression. The explanation below just seems like a normal OLS with some covariate, fixed effects.. etc. What exactly is a non-parametric regression and how do we see it from the equation below? When do we use it? The only noticeable difference from standard OLS seems to be the L function, which I don't understand.. Also, when running a non-parametric regression, is the function at STATA different from the normal xreg?



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