Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the global health-care industry to thrive as our planet's population grows and ages, the iShares S&P Global Health Care ETF (NYSE: IXJ) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.48%.

This ETF doesn't have the most impressive track record, but its future is what matters most. It outperformed the S&P 500 by a little over the past five years, on average, and underperformed it by less than a percentage point annually over the past 10. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With an ultra-low turnover rate of 6%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several of this ETF's components have made strong contributions to its performance so far this year. Abbott Labs (NYSE: ABT), up 18%, sports rising profit margins and strong fundamentals, and plans to split in two soon. Its new pharmaceuticals-only entity will be depending on anti-inflammatory-disease drug Humira for a huge chunk of earnings, which is a bit risky, as it faces competition from Vertex Pharmaceuticals (Nasdaq: VRTX), Pfizer, Incyte (Nasdaq: INCY), and others.

Other companies haven't added as much to the ETF's returns so far in 2011, but could have an effect in the years to come. Amgen (Nasdaq: AMGN), for example, gained only about 1%, but it's embarking on a big share buyback program, aiming to reduce its share count by 10%. That will leave remaining shares more valuable. It's nice, but it's also not the most exciting way to spend $5 billion -- my colleague Brian Orelli suggested that that kind of money could have been spent to buy promising companies such as Dendreon (Nasdaq: DNDN), Aeterna Zentaris (Nasdaq: AEZS), or many others.

The big picture
Demand for global health care isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about the best dividend ETFs. And if you're looking for some great investments beyond ETFs, consider these 10 stocks for your retirement portfolio.