What is the easiest way of getting a number controlled for various factors? An average.

Most people stop thinking about the consequences right about here, but the harsh reality is that in many cases, an average is a terrible idea - especially if you don't know the data you're working with in the first place!

Consider what would happen if you start using averages to fill in missing data. or the potential for disasters with trying to average qualitative data expressed as numbers.

I'll spend 20 minutes raking the concept of averages over the coals. Bring marshmallows.