But how do you find out if turnover is high? It would be interesting if you could measure this with LinkedIn - as in looking at the profiles of all developers

But how do you find out if turnover is high? It would be interesting if you could measure this with LinkedIn - as in looking at the profiles of all developers who worked for company X and determine how long they stayed on average. Of course it would rely on people actively updating their profiles. But if you could it would be interesting to see how much high turnover at a company correlated with bad reviews for said company on sites like Glassdoor.