Finally, emerging markets have a lot of people. China, India, Indonesia and Brazil are four of the world's five largest countries (the U.S. ranks third) and together account for roughly half the global population. Brazil's per-capita GDP is only about one-fourth that of the U.S.; China's is less than one-fifth. They have a long way to go.

So now, when developing markets are flat on their backs, is the time for contrarian investors to look closely at them. The easiest way to invest is to buy an ETF, such as iShares MSCI Emerging Markets, which charges 0.69 percent per year. (That expense ratio is high compared with the typical domestic ETF but lower than most actively managed emerging-markets funds.) Stocks from Asia account for 64 percent of the portfolio; Latin America, 16 percent; Eastern Europe, 8 percent; and Africa and the Middle East, the rest.

Among mutual funds, I like Vanguard Emerging Markets Stock Index (VEIEX), which tracks the FTSE Emerging index, and Harding Loevner Emerging Markets (HLEMX), an actively managed fund that has done a bit better over the long run. (The Harding Loevner fund is a member of the Kiplinger 25.) I slightly prefer the Vanguard fund because its annual expense ratio of 0.33 percent is less than one-fourth that of the Harding offering. The broad exposure to the global economy of the large-company stocks in such funds tends to dampen volatility, and they do own loads of stocks in real emerging markets, such as China, India and Brazil.

If you can absorb more risk, focus, in these dark days, on India. One of my favorite ETFs is EGShares India Consumer (INCO), linked to the Indxx India Consumer index. It holds firms that sell to the huge domestic market, including Zee Entertainment, a film- and TV-production firm; and United Breweries, India's largest beer purveyor.

Another way to get the most out of emerging markets is to invest in the stocks of small companies, which tend to have more of a local focus. Consider SPDR S&P Emerging Markets Small Cap (EWX), an ETF with an expense ratio of 0.65 percent and holdings such as China Everbright International, a developer of environmental projects, and Kroton Educacional, the third-largest for-profit education firm in Brazil.

Market Vectors Brazil Small-Cap (BRF) is an ETF whose top holding is another chain of post-secondary private schools, Brazil's Anhanguera Educacional Participacoes. It also owns Qualicorp, which offers insurance to unions and trade associations, and Marfrig Alimentos, a meat processor that is expanding to China.

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I would stay away from individual stocks of small companies and emerging-markets bonds. Bonds, too, have been clobbered in 2013, but although risks are lower than for stocks, they are still too high for the potential rewards.

You can't time emerging markets any better than you can time domestic ones, but there's no doubt that it's better to buy when investors are heading for the exits. And that's just what they're doing.

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