These stocks are proven summertime winners

• Health care has been a consistent outperformer in the June through August period.
• Oppenheimer said seasonally this is the best time for health-care bulls.
• Materials and consumer discretionary sectors have lagged the S&P 500 the most.

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Even through the dog days of August, health care has been a consistent summertime outperformer.

The S&P health-care sector has outperformed the with an average relative gain of 1.4 percent in the June through August period, since 1990.

Health care will certainly be in the headlines this summer as the Senate attempts to replace Obamacare.

Ari Wald, technical analyst at Oppenheimer, did the analysis, and says even though health care is seasonally a winner, be careful. The sector has outperformed the S&P 63 percent of the time since 1990.