Hi everyone!

I am doing my master thesis using panel data regression. However, before proceeding to estimation I did diagnostics tests such as:

1) normality test
2) multicollinearity test
3) heteroskedasticity test.

Out of these 3 tests, I didn't pass normality and heteroskedasticity tests. And what is the difference to perform a test before panel data estimation and after? This forum suggested doing it before, while my supervisor said to perform tests after the panel data regression.

Secondly, how can I now control the normality and heteroskedasticity errors in my panel data? Can you please provide me detail steps in controlling these errors?
I tried to run fixed and random effect models with xtreg and "robust" suffix to control heteroskedasticity and it was showing me that the probability is not anymore significant, what should I do now? Run pooled OLS regression?

I will really appreciate your answers.

With kind regards,
Temirlan.