Unemployment has fallen, and the stock market has soared. So why has the economic expansion since the recession been so tame, with sluggish productivity and, at least until recently, anemic wage growth?

Economists say the answer, to some degree, can be found in a start-up slump — a decline in the creation of new businesses — and a growing understanding of what’s behind it.

A total of 414,000 businesses were formed in 2015, the latest year surveyed, the Census Bureau reported Wednesday. It was a slight increase from the previous year, but well below the 558,000 companies given birth in 2006, the year before the recession set in.

“We’re still in a start-up funk,” said Robert Litan, an economist and antitrust lawyer who has studied the issue. “Obviously the recession had a lot to do with it, but then you’re left with the conundrum: Why hasn’t there been any recovery?”