One thing this methodology doesn't account for is company culture. It would be tough to predict in aggregate, though...
You could start by crawling for key words in job board posts. Companies that value, for instance, 'vacation', 'open source contributions', and '20% time' might (depending on who you are) be preferable to those listing 'nerf gun fights' and 'free beer' as perks.
Another idea would be to look at the age of the founders and early employees, as well as the schools attended. I don't have the data on this, but I suspect that a more diverse employee background would correlate with a stronger company culture. Then again, small companies will tend to hire within their personal networks, naturally selecting for people with similar backgrounds, so you shouldn't necessarily see a relatively homogenous company as a red flag, unless they are larger than ~10 employees and are actively hiring more. (Of course, if the company is very homogeneous but lines up with you exactly, that might also indicate a 'good' match.)
There are probably other ways to predict company culture, but ultimately you won't really know until you have a chance to visit their offices, meet the team, etc. But by doing a bit of research up front you may be able to narrow down your search based on a few red flags here and there.
