A significant, perhaps growing proportion of research at universities is carried out by postdocs¹. Postdocs are typically employed on fixed-term contracts. Personally, I know several people who have been employed on chains of temporary research contracts for well over ten years, including some all the way to retirement: their work is good enough to satisfy their PI, but not good enough (or perhaps not interested) for promotion. Some may seek to move to industry, not because the work is more interesting but because a permanent contract is easier to get, such as suggested in this Dutch-language article), but a response in the same article denies that there is a brain drain.
Is there any evidence for a brain drain from academia to industry, lured by permanent² contracts?
NB: although personal stories/anecdotes are interesting (I could offer my own) it would be even more interesting to see if there is actual research into this question.
Edit: I welcome answers that challenge the assumption that job security as a researcher is more easily achievable outside academia than inside. Some PhDs do of course become professors, but I've rarely seen professors that have much time to do research, as opposed to supervise research. My question supposes the perspective of people who wish to do research themselves rather than in a supervisory role.
¹I use postdoc here in the meaning of any time-limited contract which is mainly or entirely focussed on research.
²Of course, no job is certain until retirement, but getting a mortgage without a permanent contract is likely hard/impossible.