In 1980, according to the Census Bureau data, roughly one in eight companies had been founded in the past year; by 2015, that ratio had fallen to fewer than one in 12. The downward trend cuts across regions and industries and, at least since 2000, includes even the beating heart of American entrepreneurship, high tech.

Although the overall slump dates back more than 30 years, economists are most concerned about a more recent trend. In the 1980s and 1990s, the entrepreneurial slowdown was concentrated in sectors such as retail, where corner stores and regional brands were being subsumed by national chains. That trend, though often painful for local communities, wasn’t necessarily a drag on productivity more generally.

Since about 2000, however, the slowdown has spread to parts of the economy more often associated with high-growth entrepreneurship, including the technology sector. That decline has coincided with a period of weak productivity growth in the United States as a whole, a trend that has in turn been implicated in the patterns of fitful wage gains and sluggish economic growth since the recession. Recent research has suggested that the decline in entrepreneurship, and in other measures of business dynamism, is one cause of the prolonged stagnation in productivity.

“We’ve got lots of pieces now that say dynamism has gone down a lot since 2000,” said John Haltiwanger, a University of Maryland economist who has done much of the pioneering work in the field. “Start-ups have gone down a lot since 2000, especially in the high-tech sectors, and there are increasingly strong links to productivity.”

What is behind the decline in entrepreneurship is less clear. Economists and other experts have pointed to a range of possible explanations: The aging of the baby-boom generation has left fewer Americans in their prime business-starting years. The decline of community banks and the collapse of the market for home-equity loans may have made it harder for would-be entrepreneurs to get access to capital. Increased regulation, at both the state and federal levels, may be particularly burdensome for new businesses that lack well-staffed compliance departments. Those and other factors could well play a role, but none can fully explain the decline.