I doubt that there are many companies as willing or open as avast to admit there is such a thing as a false positive, let alone be open enough to have publicly available stats about the numbers of FPs they have.
All AVs, anti-malware software is likely to suffer FPs, it is how quickly they respond to and deal with FP reports. In that regard I believe avast to be excellent.
If anyone learns anything about FPs it should be, 'delete in haste, repent at leisure' your first action should be move to chest, investigate and not delete.
I believe I have only experienced 1 FP in just over a year, but then again I don't get many true virus detections either. So the more secure your system, and using common sense in your browsing habits, etc. the less likely you are to suffer either FPs or true virus detections.