Economic growth in the United States has been disappointing for more than a decade now. Some of the reasons are complex and hotly debated, and will be the subject of a series of posts here starting next week. But one of the reasons is not mysterious at all. It simply reflects demographic changes.

The share of Americans who are working age — old enough to be out of school but young enough not to be retired — is no longer growing. Only about 53 percent of the population was between the ages of 25 and 64 last year, unchanged from 2007 and up only slightly from 52 percent in 1997. Between 1967 and 1997, by contrast, the share grew 8 percentage points, to 52 percent from 44 percent. As more baby boomers retire, the share will begin to fall.



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Fewer people of working age means, obviously enough, fewer workers. It also means fewer potential entrepreneurs creating new businesses that hire people.

And aging isn’t the only demographic weight holding back the economy. For most of the 20th century, the share of women in the labor force was rising. It reached 60 percent in 1997, up from just 32 percent in 1948.

But the share isn’t rising anymore. It fell below 60 percent in the 2001 recession, spent most of the last decade around 59 percent and, in the long aftermath of the financial crisis, was only 57.6 percent last month.

The same logic applies to the female trends as the overall population trends: absent an ever-growing flow of new workers, the economy will struggle to grow as quickly.

How important are these demographic trends to the great growth slowdown of the last 12 years?

The reason that the statistic known as productivity receives so much attention is because it measures economic growth while controlling for demographics. Productivity is simply average hourly output across the economy. It is not directly affected by how many people are working.

When you look at the productivity trends, they are not quite as grim as the economic growth trends. The growth rate has fallen sharply over the last decade but it is not at a 60-year low. The average annual growth of productivity over the last decade, 1.9 percent, is somewhat below the average rate of the last 60 years, 2.2 percent.

From the mid-1990s to the early part of last decade, by comparison, productivity was growing at its fastest rate since the 1960s. So the drop-off in the past decade has been sharp.

By extension, it seems clear that demographics are an important reason that the American economy has slowed but only one part of a much bigger story.

Our mission next week will be to dig into that story. We will begin exploring the causes of the slowdown in Americans’ income growth, a result of both the slowdown in economic growth and a rise in inequality. Based on the hundreds of reader comments on our initial Agenda post and on follow-up conversations with economists, I came up with a list of 14 major potential causes.

We will post the list on Monday and invite readers to tell us which causes they believe are the most important. We’ll also tell you what we are hearing about the list from a range of the country’s top economists.