I'm writing an essay, and want to know the promotion rate and average duration from assistant professor to associate professor and associate professor to professor in recent years. Sadly I don't know the data for the US. Could anyone tell me?
The US National Science Foundation collects a lot of data from surveys of recent doctoral recipients that it publishes on this web page. The precise thing you are looking for (tenure success rate) does not seem to appear, but there is a lot of relevant information. Specific professional societies collect similar information. For instance, the American Mathematical Society publishes an annual survey of information on recent doctoral recipients; it includes data about the salaries and employment situation of recent doctoral recipients in the mathematical sciences.
Well, I'm sure this is too late for the essay, but I happened to come across some (old) data for US medical school faculty from the AAMC. They look at average number of years to promotion and percentage of faculty promoted within a ten-year period, both from assistant to associate, and associate to full, broken down into various categories (gender, degree earned, whiteness, clinical vs theory, etc).
The 10-year promotion rates, both to associate and full, are generally in the 30-50% range, and for those specifically in tenure-track positions, around 50%.
I suspect the numbers would be higher for Arts & Sciences or Engineering faculty.