I have a data set about 125 companies. For each company I have the salary and some other variables about the top 5 managers in each company. One observation contains the top 5 managers in each one of the 125 firms from 2010 to 2018, so every company has the data for its managers for each year. For some companies some years are missed or it is for less than top 5 managers. I want to check the effect of a regulation that occurred in 2016, and my question is :
Is it OK to do linear regression for the observations before 2016 at once ?, I am not sure about that because every year has the same companies with the data of that year.
Can anyone tell me if it is Ok to do that or help by advising another regression method