You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
I expect this rule wouldn't work as well as you think, because it's often possible to see how a study would be biased given its methodology.
It was a joke. It'd work exactly as well as I think (i.e., it wouldn't work, as indicated by my use of "Tongue-in-cheek"). Though I do think this is an interesting set of questions to think about.
I knew you didn't think it would work; I expected that this specific aspect hadn't occurred to you and was relevant.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.
Tongue-in-cheek rule: you can only see the result of a study when you've first approved or disapproved the methodology. The result is then approvingly tweeted by you, no matter what the result was.