Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some mega caps -- stocks with massive market capitalizations -- to your portfolio but don't have the time or expertise to hand-pick a few, the Vanguard Mega Cap 300 Value Index ETF (MGV -0.26%) could save you a lot of trouble. Instead of trying to figure out which stocks 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. This ETF, focused on mega caps, sports a tiny expense ratio -- an annual fee -- of 0.11%. It also offers a dividend, recently yielding nearly 2.3%.

This mega-cap ETF has lagged the S&P 500 over the past three and five years, but over the past year, it has outperformed its large-cap value category. 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.

Why mega caps?
Large companies can add some ballast to your collection. The biggest -- i.e., mega caps -- may not grow as briskly as their smaller counterparts, but having reached their current size, they likely have some strong assets and features. And some can grow quite briskly, too.

More than a handful of mega caps had strong performances over the past year. Bristol-Myers Squibb Company's (BMY -0.52%) stock, for example, has soared 45% over the past year. The company has been focusing more on specialized, niche drugs lately and less on formulas for widespread conditions. It's also shedding businesses where it sees slower growth or less profitability, such as its stake in a diabetes joint venture. Bristol-Myers Squibb has new formulas in its pipeline, targeting cancers and viruses, and has particular strength in immuno-oncology. It recently got FDA approval for its body fat disorder drug, Myalept. Bristol-Myers Squibb stock yields 2.6%.

Occidental Petroleum Corporation (OXY -2.22%) gained 17%. The oil company is spinning off its California assets and will focus more on operations in the Permian Basin, where it has been the largest producer. Its efficiency has improved substantially there thanks to advances in fracking technology. Occidental Petroleum stock offers a 3% yield.

Other mega caps didn't do quite as well over the last year, but could see their fortunes change in the coming years. General Electric Company (GE 1.99%), up 11% over the past year, has been transforming itself lately, becoming much more of an energy company, with oil and gas now its fourth-largest revenue generator. Part of General Electric's transformation involves spinning off its sizable retail finance business. GE's fourth quarter featured revenue up 3% over the year-ago quarter, earnings per share up 20%, and its order backlog growing by 8% to a record $244 billion. The company's CEO buying millions of dollars worth of shares is appealing, too. GE stock yields 3.4%.

Domestic tobacco titan Altria Group (MO -0.49%), up 12%, faces headwinds such as rising taxes, regulations, competition from discount cigarettes, a shrinking smoker base, and even counterfeit cigarettes. Bulls are hopeful about its move into electronic cigarettes (one analyst even sees them eclipsing regular cigarettes within a decade) -- but the FDA might regulate those, too. Altria's fourth-quarter results were disappointing, with Marlboro volume shrinking by 5.7% over year-earlier levels. Still, Altria offers a hefty dividend yield of 5.2%, along with substantial free cash flow to support it. That's a compelling income stream.

The big picture
If you're interested in adding some mega caps to your portfolio, consider doing so via an ETF. 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.