My conclusion was that:
* some interview problems carried zero signal
* some interviewers are really good at identifying strong candidates, and others correlate negatively! On average interviewers rating is a weak signal (<0.25. Correlation)
* geographic location is a medium signal (0.2)
* a relevant degree is a strong signal (0.4)
* choice of programming language is the strongest signal (>0.8 correlation (or anti-) for some languages, and some.
There is some selection bias though since candidates who were rejected did not get a chance at the job so we didn’t have a rating for them.