They're still better than basing your opinions on anecdotal data. For example, I previously believed that the majority of HN users were in the Bay Area, mostly

They're still better than basing your opinions on anecdotal data. For example, I previously believed that the majority of HN users were in the Bay Area, mostly because it seems like users mention that they're there a lot. I was probably basing that opinion on less than a dozen data points.