It may not be the only explanation for abysmally slow job growth. But it’s a powerful one.

Startups are starting smaller. They’re not adding jobs at the rate they have in the past. There are fewer of them. And not as many startup businesses are surviving as once did.

Those are some of the conclusions of an analysis of Census and Bureau of Labor Statistics data released this morning by the Ewing Marion Kauffman Foundation for Entrepreneurship. And the analysis goes a long way toward explaining slow job growth that actually predates the Great Recession of 2007 to 2009.

As the authors write in their report:

In fact, since 2006, the annual number of new employer businesses tracked in government statistics has plummeted 27 percent for new independent firms and approximately 23 percent when considering a broader measure of new “establishments” (new independent businesses and new expansions of existing businesses).

Another important, but often overlooked, measure is the rate of business survival for all new firms.

Somewhat remarkably, the overall trend in this statistic was relatively stable prior to the Great Recession, with roughly 45 percent to 50 percent of new businesses surviving five years. Recent business births, however, are showing starkly lower survival rates.

Sixty-one percent of firms born in 2007 survived for two years, while 65 percent reached that threshold in earlier periods. It’s even worse if you look at five-year survival rate. For firms born in 2004, less than 45 percent have survived.

What that means is one of the most important engines of job growth in the United States is suffering, has been suffering since before the onset of the recession in 2007, and conditions for startups have worsened even as the economy in general has slowly recovered from the disastrous years at the turn of the decade.

Not only are fewer startups surviving, those that do find their footing are doing it with fewer employees. Back in 2002, the average startup got off the ground with 10.8 employees. In 2009, that figure had fallen to “fewer than 8 employees.”

The jobless rate has grown every month for the past three months, and now stands at 9.2 percent, a government report released Friday shows.

Emerging businesses are hugely important to that rate, the Kauffman report shows, and startups haven’t been pulling the weight they have in past decades.

The authors write: "Startups created an average of 3.5 percent of total U.S. jobs annually in the 1980s, but in the 2000s contributed only 2.6 percent of total U.S. jobs. While diminished in number, these jobs still were the difference between positive and negative overall net job growth in the United States."

In fact, employment at startups has been declining since the tech bubble burst. It hit a high of about 4.7 million new jobs a year from 1997 to 2000 and had fallen to about 2.5 million in 2010.

The conclusions in the report point to a major challenge for policymakers: How can they encourage more and healthier startups that hire more workers? Because if no one can figure that out, the new normal may well be unemployment in 9-percent range.

"While the recession certainly deepened the jobs deficit, the U.S. economy stopped producing enough new jobs well before the downturn," said Robert Litan, Kauffman Foundation vice president of research and report coauthor. "Historically, startups are the key to long-term employment growth, and they have been hiring fewer people for the last several years. We won’t fix our core unemployment problem in the United States until young businesses get back on track."