It's a truism of stock investing: The surest way to make money is to pinpoint well-managed companies that provide products and services everyone must have into the foreseeable future.

Few necessities are as crucial as medical care. Add a graying population and the expansion of federal health coverage to the mix, and UnitedHealth Group (UNH - Get Report) , the nation's largest health carrier, should outperform over the long haul.

With a market share of 13.6% and more than 84 million policyholders, UnitedHealth is not to be taken lightly. The stock did get clobbered last Thursday in the wake of its earnings release. By the time the market closed on Thursday, UnitedHealth shares had regained some of their earlier intraday losses but they were still down 1.6% at $120.17. They're slightly below that level on Monday. The recent selloff just makes this stock a rare bargain.

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Think of it as the health-industrial complex: Health-related spending in the U.S. now approaches $3 trillion annually and continues to grow every year.

Whether you think the Affordable Care Act, a.k.a. Obamacare, is socialism run amok or sound public policy is immaterial. As an investor, you should be shrewd enough to put aside your political bias and focus on the fact that Obamacare is the law of the land and it will generate massive growth for select companies.

Obamacare winners include Humana (HUM - Get Report) , Pfizer (PFE - Get Report) , Merck (MRK - Get Report) and Johnson & Johnson (JNJ - Get Report) , but none of them are getting punished right now as badly as UnitedHealth.

Investors are too preoccupied with the mixed operating results that UnitedHealth unveiled last week. Fact is, this health behemoth remains well positioned to capture a major chunk of the health sector's future spoils.

With a market cap of $114.5 billion, UnitedHealth provides health benefit plans for individuals and public and private employers of all types and sizes. Among the company's health insurance and delivery products are pharmacy benefit management plans, benefit plan design, and claims processing services.

UnitedHealth last week announced third-quarter results that actually beat earnings and revenue forecasts, but not by as big a margin as investors were hoping for. The culprit for these modestly disappointing results was the company's higher costs and lower profit margins, but this probably is a temporary bump in the road. These higher costs actually bode well for future growth, as the company invests in promising segments such as Medicaid health maintenance organizations.

UNH posted third-quarter earnings per share of $1.65, up from $1.63 a share in the same quarter a year ago and a penny ahead of Wall Street's consensus. Revenue jumped 27% year over year to $41.5 billion, beating the consensus estimate of $40.17 billion. Investors were spooked, however, by higher costs, as the company spends more to achieve higher ratings under Medicare's five-star rating program that designates how much insurers reimburse services.

Management maintained its full-year 2015 EPS guidance of $6.25 to $6.35, a sign that the company remains on the right track over the long haul.

UnitedHealth's greatest growth potential lies in the field of Medicaid, the federal-state program that provides health care for the poor. A major reform wrought by Obamacare is that millions of lower-income Americans without health coverage will qualify for Medicaid.

The nonpartisan Congressional Budget Office projects that 11 million to 16 million needy Americans will be newly insured through Medicaid by 2016. States now pay about half the cost of this coverage; Obamacare offers federal financial assistance for states to expand coverage.

This Medicaid expansion started in January 2014, steering millions of new customers through the doors of Medicaid HMOs. UnitedHealth Group is the leader in the Medicaid HMO market and should see Medicaid revenue swell in future quarters.

With a strong balance sheet, an edge in the booming Medicaid business and optimistic EPS guidance for full-year 2015, UNH should withstand the market volatility that we're likely to experience for the rest of this year and into 2016.

Now sporting a trailing 12-month price-to-earnings ratio of only 19, UnitedHealth Group stock is an incredible bargain if you consider that the broader health care sector has a P/E of 44.5.

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John Persinos is an editorial manager and investment analyst at Investing Daily. At the time of publication, the author held no positions in the stocks mentioned.