I'm not sure if you can read the link below, but it's a wall street journal report on whether stock research appears more reliable with recent changes. But note two things, the average four year return for these research firms recommendations is about zero. And the only two firms that have positive recommendations on GM, appear to have investment banking business with GM.
WSJ report on analyst recommendations.
Which leads me to the conclusion that wall street research still has inherent biases, and usually worthless.