Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect media-related companies to thrive over time as our growing population craves more information and entertainment, the PowerShares Dynamic Media ETF (NYSE: PBS) 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 0.63%. The fund is on the small side, too, so if you're thinking of buying, beware of occasionally large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has performed rather well, trouncing the world market over the past three years and beating it over the past five. 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?
More than a handful of media-related companies had very strong performances over the past year. Lionsgate Entertainment (NYSE: LGF) soared 117%, managing a movie library of more than 12,000 titles and putting out about 12 to 15 new films per year. Its television production and syndication division boasts titles such as Mad Men, Nurse Jackie, and Weeds. The company has been expanding into Asia and has grown its revenue eightfold over the past decade.

Madison Square Garden (NYSE: MSG) surged 77%, posting strong revenue and earnings numbers in its last quarter. Its future rests largely on its broadcast deals, but factors such as NHL labor disputes can disrupt its performance. Meanwhile, the company's president recently resigned, and with a forward P/E of about 30, the stock doesn't look like a bargain right now.

Sirius XM Radio (Nasdaq: SIRI), up 70%, is broadening its scope, recently inking a deal with Nissan to offer "telematics" services such as roadside assistance and stolen-vehicle tracking. The company has been boosting its subscriber rolls and its prices, but some worry about its dependence on carmakers as well as competitive threats from Pandora and even Apple. Meanwhile, leadership turnover appears to be around the corner, which can introduce uncertainty.

Marketing, events, and tourism specialist Viad (NYSE: VVI) advanced 25%, and telegraphed a lot of confidence in itself with a 150% dividend increase recently. In its second quarter, revenue and earnings rose 3% and 36%, respectively, over year-ago levels, and management noted that it expects 2012 to be stronger than 2011 due to cost-cutting and restructuring.

The big picture
Demand for media 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.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.