At first glance, the stock market in 2016 is nothing like it was last year, when winners kept winning and gains seemed to be concentrated in a handful of stocks.

Nowadays leadership bounces around. Since January, the S&P 500 Index’s strongest group has shifted among utilities, energy producers and technology companies, as investors swapped defensive shares for those that respond to economic growth.

At the same time, not all is well in the breadth department. One ominous signal that marked trading in 2015 has begun to reassert itself, a pattern in which the benchmark index hovers near a 52-week high while the proportion of stocks that are similarly elevated dwindles.

Such divergences, measured by comparing the S&P 500 and the number of constituents trading above their 50-day moving average, have been rare since 1990 — and are generally bad news for investors. In the seven instances that occurred before this year, all but two portended further losses in the next three months, with the S&P 500 falling a median 1.3 percent, according to data compiled by Sundial Capital Research Inc.

“This recent weakening in breadth is troubling,” Jason Goepfert, president of Minneapolis-based Sundial, wrote in a note to clients. “It rarely ends well for stocks — usually, the indexes follow breadth as opposed to the other way around.”