The Dow Jones Industrial Average, also known as the DJIA or simply as "the Dow," is made up of 30 stocks and is designed to give a snapshot of how American big business is doing. So far in 2018, the Dow hasn't performed too well. As of mid-July, the index is up by just 1.6% for the year.

However, there's a wide variety of performance among those 30 Dow components, and not all have been so-so investments in 2018. In fact, here are five Dow stocks that have outperformed the index by more than 10% over the past six and a half months and why each has done so well.

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Company (Symbol)

Recent Stock Price

Market Capitalization

Year-to-Date Price Change

Nike (NYSE:NKE)

$77.78

$99.8 billion

24.3%

Microsoft (NASDAQ:MSFT)

$105.94

$813.9 billion

23.9%

Visa (NYSE:V)

$139.70

$249.5 billion

22.5%

Boeing (NYSE:BA)

$357.04

$208.0 billion

21.1%

UnitedHealth Group (NYSE:UNH)

$249.90

$240.1 billion

13.3%

Data Source: TD Ameritrade. Prices, market capitalizations, and YTD performance as of July 17, 2018.

An impressive turnaround

Nike is the best-performing Dow component of 2018 so far. After a few difficult years, it seems like the athletic-wear giant has gotten its groove back. Despite rising revenue, margins had been steadily falling due to a highly competitive environment.

Well, the most recent quarterly report showed that things might be changing. As my colleague Travis Hoium recently wrote, Nike's revenue jumped 13% in the company's latest quarter, and margins finally started to move higher. Its push to grow its digital channels appears to be paying off as well, with digital commerce revenue up 25% over the past ear. Furthermore, Nike's sales in high-growth China were especially impressive, up 35% year over year. This combination of sales growth and increasing profitability has propelled the stock significantly higher over the past few months.

A strong tech market makes Microsoft a close second

Tech behemoth Microsoft is just behind Nike for the year in terms of performance. To put it mildly, the tech market has been on fire lately -- just look at the performance of the FANG stocks through the first half of the year.

To be clear, this isn't a late-1990s style tech bubble. Rather, the performance is backed up by solid numbers (at least in Microsoft's case). Microsoft's sales are up 16% over the past year and net income is up by a staggering 35%. Analysts are expecting the company's upcoming earnings report to be even better, so it's no surprise that Microsoft is one of the best performers on the light-on-tech Dow.

The leading payment processor has been on fire

Visa's stock price is up by more than 22% this year, and this is just the latest in an extremely impressive performance history. Over the past decade, Visa's stock price (split-adjusted) has increased by more than 670% on the rise in e-commerce and impressive revenue growth -- especially internationally. In the latest quarter, Visa's international transaction revenue jumped by 19%.

With e-commerce continuing to increase year after year and the "war on cash" dramatically increasing card payment volumes all over the world, Visa's growth story could continue for years to come.

Boeing is keeping busy these days

Aircraft manufacturer Boeing is another stock that has steadily outperformed for years, up by 445% over the past decade. In a nutshell, airplanes are selling extremely well right now.

There are several reasons for Boeing's 2018 success as my colleague Lee Samaha reported. The 787 Dreamliner is selling well, the company is producing the popular 737 aircraft in increasing volume, and Boeing boosted its full-year guidance in its latest earnings report. The aviation industry as a whole is doing quite well, and if this continues, Boeing could have even more growth ahead.

Strong numbers from this health insurer

Despite a small dip after issuing its second-quarter earnings report, health insurance giant UnitedHealth Group still finds itself in the Dow's top five stocks of 2018 so far.

The big catalyst for UnitedHealth was a strong first-quarter earnings report, in which the company increased its full-year guidance. In fact, until that time, the stock was roughly flat for the year -- virtually all of the gains are since its mid-April earnings report. To be sure, the second-quarter earnings were quite strong, with 12% revenue growth and nearly 28% earnings growth, plus the company raised its full-year guidance yet again.

Teresa Kersten is an employee of LinkedIn and is a member of The Motley Fool's board of directors. LinkedIn is owned by Microsoft. Matthew Frankel has no position in any of the stocks mentioned. The Motley Fool owns shares of Visa. The Motley Fool recommends Nike and UnitedHealth Group. The Motley Fool has a disclosure policy.