The Newsday Long Island Bloomberg Index of 30 publicly traded companies in Nassau and Suffolk counties edged down 2.8 percent in 2015, in line with bellwether U.S. indexes, despite strong returns from Cablevision Systems Inc. and Henry Schein Inc.

The tepid returns for the Long Island index were in line with the Dow Jones industrial average and the widely followed Standard & Poor’s 500 index. The Dow lost 2.2 percent, while the S&P edged down 0.7 percent. The returns for the three indexes don’t include dividends.

All three indexes were treading water at year’s end with the last trading day on Thursday determining whether they finished with gains or losses for the year.

The loss on the Long Island index followed a 12.6 percent gain in 2014.

Charles Massimo, chief executive of Deer Park-based CJM Wealth Management, said that in 2015 the U.S. stock indexes took a breather after a multiyear rally but never collapsed despite “all the doom and gloom” over rising interest rates and weakness in China’s economy.

For 2016, Massimo said that anticipation of rising interest rates already is “built into stock prices” and, barring a “huge spike,” the rate increase is unlikely to jar the market.

Still, Massimo said he would be “very cautious” about domestic markets, preferring to look overseas for value.

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The stock of Bethpage-based Cablevision, which owns Newsday, was the top performer in the index with a 54.6 percent gain in 2015, following a buyout offer worth $17.7 billion, including debt assumed, by European cable operator Altice NV. The calculation, from Bloomberg, doesn’t include dividends.

Other major Long Island index components were scooped up in what researcher Dealogic said was a banner $5 trillion year worldwide for mergers and acquisitions. Pall Corp. was bought for $13.8 billion by Danaher Corp., and Dealertrack Technologies Inc. was acquired for $4 billion by Cox Automotive Inc.

Massimo said he expected an even bigger spike in M&A in the early part of 2016 as acquirers seek to take advantage of interest rates that remain at historically low levels.

Henry Schein, the largest publicly traded Long Island company by revenue, posted a 16.2 percent gain for the year. The Melville-based distributor of dental and health care products, whose stock closed the year at $158.19, accounts for about 19 percent of the Long Island index, which, like the Dow Jones industrial average, is weighted by share price.

The S&P 500, in contrast, is weighted by companies’ stock market capitalization.

The largest sectors in the Long Island index are health care — Henry Schein and two other companies — accounting for 27.6 percent, and financials, 11 companies accounting for 27 percent.

When dividends are added, the Long Island index moved into positive ground, returning 1.3 percent, according to Bloomberg.

The worst performer in the index for 2015 was Veeco Instruments Inc. The stock of the Plainview maker of equipment for producing light-emitting diodes tumbled 41.1 percent in 2015 amid weak demand from its customers in Asia. Veeco didn’t respond late Thursday to a request for comment.