An index designed to predict the future health of the U.S. economy posted a fourth straight solid gain in December.

The Conference Board says its index of leading indicators increased 0.5 percent in December after a revised gain of 0.4 percent in November. The index also posted solid gains in September and October after a flat reading in August.

The December increase reflected strength in a number of components of the index. Conference Board economists said this suggested the economy was gaining momentum at the end of last year.