A few years back in an interview I remember being asked to derive the Sharpe ratio from the correlation between a pre-open daily signal and the open-close returns. I think you had to make some assumptions regarding the risk/reward and accuracy but you could start with a correlation of say 0.05 and back out a sharpe ratio.
I'm interested in revisiting this and can't seem to find anything similar online. Anyone know of any resources?
Update: Happy with comment answer, thanks!