The index of leading economic indicators increased in December for a second consecutive month, the Conference Board reported Thursday, pointing to sustained, gradual growth.

The Conference Board, a private research group, said Thursday that its Index of Leading Economic Indicators rose 0.2 percent last month, following a revised gain of 0.3 percent in November. The increase, which was in line with economists’ forecasts, pushed the index to 115.4, still below its high of 116.5 in May.

The gains in the index, which is intended to predict economic activity over the coming three to six months, followed five months of decline.