Market research for video games?

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My Business Intro 101 project is to make a business plan based around passion/interest/skills. I chose video games as a passion, as I do plan to one day own my own Indie business(After working for other companies for a couple of years).

Part of the assignment requires us to do market research for our business plan. So I'm researching online and now I'm thinking: How should I go about doing this? How do I do market research for video games? Or more specifically, because they are the games I want to develop, how do I do market research for online social games and RPGs?

Wouldn't it be impossible for me to tell how well/bad my game would sell based on history of sales of OTHER games? And would it even be a good idea to base my games on those sales?

I think the people who do that just wind up making some cheap reamake of World of Warcraft and Call of Duty, or Angry Birds(we've all seen plenty of those, and it's just so obvious when you see them).

Also, I plan to make PC/Online games with my main source of profit coming fromicro-transactionsns.

Where can I find a list of sales of a certain game? More specifically, one that is digitalldistributeded.

Please list ANY and ALL resources & findings on the subject. I WILL choose you as best answer just for this.