AMC Entertainment drama is exposing risks in $11 trillion world of indexing

 The difference now is that investors have poured billions of dollars into products tracking smaller and cheaper stocks in the past six months

Index funds are supposed to cut out the human-driven craziness that periodically infects markets, but the recent meme-stock fever proved the $11 trillion industry is far from immune.

The remarkable surge in shares of AMC Entertainment Holdings and a handful of other stocks is showing up in multiple exchange-traded funds, skewing portfolios, altering risk profiles, and exerting outsized influence on prices.

Take the $68 billion iShares Russell 2000 ETF (ticker IWM). In the past week through Thursday, AMC powered 70 percent of the product’s advance. The stock was responsible for less than a 10th of the fund’s return in the previous week.

It’s a timely reminder that even diversified funds on autopilot remain subject to the whims and eccentricities that frequently lash markets out of nowhere.

“For index investing, the appeal is that human decision-making, human emotions are taken out of it,” said Tom Essaye, a former Merrill Lynch trader who founded “the Sevens Report” newsletter. “That works all well and good until a stock that is supposed to be 50 basis points of the fund now becomes 6 percent.”

The AMC effect can be seen across a range of funds. Alongside IWM, the $17.5 billion iShares Russell 2000 Value ETF (IWN) and $72 billion iShares Core S&P Small-Cap ETF (IJR) have also seen the stock’s influence climb.