Most police departments have web sites that display statistics on the types of crimes reported in a given area. the ones to watch out for are categories like "armed robbery" and "larceny from a person." These are the main crimes that affect commuters on bikes. **** is a concern for women, but the sex crime statistics are not very helpful, as they lump acquaintance **** with stranger ****. Most "assaults" are either domestic or criminal on criminal, I believe.
I found it was very reassuring to check my PD's web site and find that most of the crimes along my inner city route were drug related or domestic. I ride (literally) right through an open-air crack maret every night at 11:45. I have not had any problems with these dealers in the last 5 years. I worry much more about their intoxicated customers crashing into me with their cars.
The other thing I worry about is crazy sadistic people looking to hassle or even hurt me "just for fun." But this is quite rare, of course. And this is where it's important not to let any strangers get physically close to you.