While I am familiar with sites such as alexa and quantcast that show traffic on an individual basis, I cannot find a method of conducting more broad analysis.
Any ideas?
Last year my co-founder and I spent a good month basically doing data entry trying to quantify our target market. I'm very confident that no one knows as much about it as we do now. It's hard work, but it's worth it.
Just keep your scope and data points the same across everything you're quantifying otherwise the data is useless. Check the same months in the same years, use the same tool (Compete, Alexa, etc. all report different numbers, we stick with Compete which generally underreports actual traffic but it's consistent).
My advise, just get a general idea in this case just make a few assumptions. Get the number of total unique users across all sites for a given month, then divide that number by how many sites you think the average gamer frequents. That should give you a pretty damn good estimate. The most important thing is TALK TO THE CUSTOMER, research and stats hold nothing compared to understanding your customer.
I will definitely use your method for estimating the size. I just feel, however, that there's a tool out there that lets me analyze unique traffic to a range of sites instead of only a single one.
TAM, SAM and SOM. These stand for total available market, serviceable available market and serviceable obtainable market.
You should start by looking into these.
Here's a quick guide to each http://tamsamsom.blogspot.com/2009/03/tam-sam-som.html
You can also use Facebook's ad platform to see how many people fit specific targeting parameters.
These aren't perfect tools, but if you use them in conjunction with other tools you could find some pretty useful market size information.