After nine years of relatively smooth sailing, U.S. equity investors have been hard hit with a wave of volatility, driven by a variety of concerns including global trade tensions, rising interest rates, tightening monetary policy and broader geopolitical uncertainty. Such fears have dragged on the S&P 500 index, which is up a modest 1.6% year-to-date (YTD) as of Monday afternoon. (See also: Trade War Could Tip US Into Full Recession: BofA.)

The 10 worst-performing stocks in the S&P 500 index in the first half of 2018 include L Brands Inc. (LB), Dentsply Sirona Inc. (XRAY), Unum Group (UNM), Brighthouse Financial Inc. (BHF), Incyte Corp. (INCY), DISH Network Corp. (DISH), Symantec Corp. (SYMC), Invesco Ltd. (IVZ), Goodyear Tire & Rubber Co. (GT) and Albemarle Corp. (ALB). (See also: Best Performing S&P 500 Stocks So Far in 2018.)

Industry Disruption, Changing Consumer Preferences 

Many of this year's poorest performers have been impacted by widespread disruption in their industries, such as traditional health care providers with the entrance of Amazon.com Inc. (AMZN), which just bought pharmacy delivery company PillPack in another multi-billion-dollar deal. Others in industries such as apparel retail have been similarly hit by the e-commerce revolution, failing to convince investors that they can innovate and transform fast enough to meet rapidly changing consumer preferences. 

Shares of Victoria's Secret parent company L Brands, down over 40% YTD and the most out of any other S&P 500 component, have suffered on investor concerns regarding piling inventories and a new level of competition from brands like American Eagle Outfitter's Aerie. Earlier this year, analysts at Jefferies criticized the clothing giant for increasing its promos in desperation to save its "broken" Victoria's Secret brand, which accounts for about 60% of L Brand's total sales. 

DISH Network, down more than 30% YTD, saw its shares crash in May on news that the company would not partner with a TV network anytime in the near future. As the satellite-TV businesses shrinks in favor of direct-to-consumer streaming offerings from platforms like Netflix Inc. (NFLX), DISH's new Sling TV has been slow to offset a drop off in revenue from traditional subscribers. (See also: Why 3 Big Cable Stocks Face Steep Declines.)

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