Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect consumer products companies to prosper as our domestic and global population grows and economies improve, permitting more purchasing, the PowerShares Dynamic Consumer Discretionary ETF (NYSE: PEZ) 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 PowerShares ETF's expense ratio -- its annual fee -- is 0.60%, which is a bit steeper than some other ETFs, but far lower than the typical stock mutual fund.

This ETF has performed reasonably well, beating the S&P 500, on average, over the past five years. 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.

What's in it?
Several consumer stocks have done very well over the past year. McDonald's (NYSE: MCD) surged about 39%, offering inexpensive fare to people pressured by our difficult economy. It hasn't been complacent over the years, either, as it has added items such as fancy coffees to its menus and is expanding aggressively abroad. Since 1980, the stock has advanced 8,000%!

Not as venerable, but also with an impressive long-term record, is priceline.com (Nasdaq: PCLN), up 20%. Much of its recent success stems from explosive growth in its international division. Some see the stock as overvalued, but it has long looked that way while it has kept growing.

Other consumer companies haven't done as well lately but could rebound in the future. Ford (NYSE: F) and vehicle component maker Tenneco (NYSE: TEN), down 31% and 32%, respectively, are good examples. Our sluggish economy has had many consumers delaying car purchases -- indeed, the average age of an American's car recently hit an all-time high of 10.8 years.

Ford has been turning itself around well, though, and its revamped Fusion looks to be a strong competitor for the Camry and Accord. Fool analyst Jacob Roche isn't so excited about Tenneco, though, noting recently that its debt is massive, with interest threatening the company's ability to service the debt.

The big picture
Demand for consumer discretionary products tends to drop during tough times, but it won't go 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 5 ETFs that could soar in 2012. And if you're looking for some great investments beyond ETFs, consider these 12 dividend stocks for 2012.