I am running an international regression, the number of observations and adjusted R-squared is as below
In Column 1, we only consider the effect of a leniency law without any additional controls, and, in Column 2, we add firm-specific variables and several other variables to capture macroeconomic conditions, in Column 3, we add some industry-level variables, In Column 4, I excluded the industry-level variable and add industry * year fixed effects, In column 5, I added region * year fixed effect. And In the last column, I exclude US out of my sample.
I follow Dong, 2019 and his result is like below, and he did not concern the number of observations
I am wondering if I should concern the change in the number of observations and normally when we should concern the change in the number of observations?