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How useful is the PEG Ratio for large cap stocks?
It is not so useful because you are applying it to large capital. Think about Theory of Investment Value. It says that you must find undervalued stocks with whatever ratios and metrics. Now think about the reality of a company. For example, if you are waiting KO (The Coca-Cola Company) to be undervalued for buying it, it might be a bad idea because KO is already an international well known company and KO sells its product almost everywhere...so there are not too many opportunities for growth. Even if KO ratios and metrics says it's a good time to buy because it's undervalued, people might not invest on it because KO doesn't have the same potential to grow as 10 years ago. The best chance to grow is demographics. You are better off either buying ETFs monthly for many years (10 minimum) OR find small-cap and mid-cap companies that have the potential to grow plus their ratios indicate they might be undervalued. If you want your investment to work remember this: stock price growth is nothing more than You might ask yourself. What is your investment profile? Agressive? Speculative? Income? Dividends? Capital preservation? If you want something not too risky: ETFs. And not waste too much time. If you want to get more returns, you have to take more risks: find small-cap and mid-companies that are worth. I hope I helped you!