If you own funds or ETFs and you're watching the market slide, you understandably might be concerned. In fact, some of you might even be worried enough to consider making a change to your fund investments or overall allocation. But that's probably a bad idea.

Before I explain why, here's a bit of perspective: My Morningstar colleagues and I conduct research on thousands of funds and ETFs globally. We assign a rating to every fund we analyze, with that rating signaling our level of conviction in the fund's future prospects. While the rating isn't advice, it offers a sense of how strongly we believe a fund is likely to outperform or underperform in the future.