The top five companies in the S&P 500 — Apple Inc., Microsoft Corp., Alphabet Inc., Amazon.com Inc. and Tesla Inc. — account for 21 per cent of the index, creating risk for equity investors because any big declines from those shares can quickly steer broader markets lower.
When the S&P 500 peaked in October 2007, it lost 57 per cent of its value when it finally hit its low in March 2009 in the wake of the global financial crisis.