Basically, the reason for a country's "brain drain" is because these "brains" (so to speak) are not appreciated and/or required in that country. The determinants that TS listed all boil down to whether the human resource of that country is being truly appreciated and, if so, justly rewarded. Yes, political stability does play a part, and for some a very important part, but at the end of the day people still go where the rewards are after taking into consideration the opportunity costs.