Just because U.S. corporate profit growth has ground to a halt doesn't mean the impact of earnings announcements in the stock market has diminished. In fact, it's never been bigger.

Swings such as Alcoa Inc.'s 11% plunge last week have become increasingly common since the financial crisis, according to a study by Leuthold Group that looked at how shares reacted in 193,000 instances going back to 1996. The Minneapolis-based fund manager found that earnings-day stock moves exceeding 5% doubled in seven years, even as the accuracy of analyst forecasts deteriorated only slightly and market volatility stayed the same.

Some investors pin the trend on the rise of computerized market makers whose hair-trigger algorithms have supplanted the deliberation of their human predecessors. To others, the swings are evidence not of a faster market, but a slower one. They say the likely culprit is the meteoric rise of passive index funds, which fail to appreciate differences among companies and their shares, throwing the process of price discovery out of whack.