Southwestern Energy Company ( SWN ) was the biggest decliner on the S&P 500, falling almost 11% to $13.15. Concerns over the U.K.'s potential exit from the European Union and a disappointing May CPI report from China contributed to investors' anxiety. Conclusion In over 50 years of studying equity investments, I have never observed a stock market that rose for so many months against such a plethora of bad news.