Consumer prices in the metropolitan region fell last month compared with a year earlier on a sharp drop in the cost of energy.

The federal Bureau of Labor Statistics reported Friday its consumer price index for the 31-county region that includes Long Island declined 0.1 percent in March compared with a year ago.

It was the second year-over-year drop of 2015; the index was off 0.5 percent in January.

The last time there was a decline, year over year, was in September 2009.

Martin Kohli, the bureau's chief regional economist, said the decreases were unusual. "It's the volatility of energy prices, and in particular big, big double-digit changes in gasoline, that gives us every few years ... an over-the-year decline in CPI."

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Gasoline prices were down 32.5 percent last month compared with March 2014. Natural gas and electricity were off 19.7 percent and 8.5 percent, respectively.

The cost of groceries increased 2.5 percent in March compared with a year earlier.

Residential rents were up 3.1 percent, year over year.

Clothing prices rose 4.3 percent, while the cost of medical care climbed 3.8 percent.