Has anyone ever been challenged to pick a stock (within the S&P 500) that will beat the S&P 500? I am wondering what factors people look at to tell the strength of a stock or index or the weakness of another. I've attached a picture of the QQQ index and the DIA index on the same chart. Notice how one outperforms the other for a while (by moving higher), then the other outperforms the one for a while (by losing less). What factors could I have looked at to get clues about one being stronger? And what could I have looked at to get clues that they were about to change dominance? This may be a fundamental analysis question, but any suggestions?