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The U.S. volunteer rate has hit its lowest level in 14 years, according to a new report from the Bureau of Labor Statistics, declining from 25.3 percent in 2014 to 24.9 percent in 2015.

"That is significant," said Nathan Dietz, senior research associate in the Center on Nonprofits and Philanthropy at the Washington, D.C.-based Urban Institute. The volunteer rate was relatively stable in the mid-2000s, he said, but "now we are seeing declines. We should probably take notice because something is going on."

Dietz said the recession is now far enough in the past that it probably isn't responsible for current declines. The volunteer rate was 27.4 percent in 2002 and peaked in 2005 at 28.8. The current slide began in 2012.

There is some good news, however. Other surveys show that the total number of hours contributed to volunteer work is staying the same, even as the overall volunteer rate declines, Deitz said, meaning that the people who are volunteering are giving more time on average.

People may also be engaging in solving community problems in ways other than volunteering, he added. "It's not always bad news when we see the volunteer rate decline."

Dietz also pointed out that the volunteer rate today is higher than in 1989 and about the same as in 1974.

"Volunteer rates have never been as high as 30 percent nationally and they've never been as low as 20 percent nationally," Dietz said. "They've always been in that fairly narrow window."

Roughly 62.6 million people volunteered at least once between September 2014 and September 2015, the report found.

The survey was conducted in conjunction with the Census Bureau's Current Population Survey in September 2015. It asked 60,000 households about the activities of civilian members of the household age 16 and older, and it defined volunteers as people who did unpaid work through or for an organization.

The survey reveals several other trends in volunteering:

1. Women volunteer more than men — and they engage in different activities.

The volunteer rate for women is more than six points higher than the rate for men, and the gap hasn't changed over time. This past year, the rate among women — especially women without children — showed a significant decline, said Megan Dunn, economist at the BLS.

The gap raises some interesting questions, Dietz said. Women are more likely to be engaged with school-based organizations, and if there are kids at home, they might be the parent less likely to work or work part-time, he said.

Dunn also said another gender divide stood out to her: the fact that men and women engage in different volunteer activities. Men were most likely to perform general labor or to work with sports teams, while women were most likely to provide food, to tutor or teach, or to fundraise.

2. People in midlife are most likely to volunteer, but their rates are declining the most.

The typical pattern for volunteering over the life cycle is for rates to be high among teens, lower among young adults, high in midlife and tapering off after that, said Dietz. One reason for the high levels among those age 35 to 54 is that people with children living at home are more likely to volunteer.

This year, however, Dietz was concerned to note declines among those age 35-44, whom he calls the "backbone of the volunteer force."

But he noted that there was an increase among those age 25-44, which bodes well for the future.

"Every generation at this (age) gets an unfair reputation for being lazy and self-absorbed … but the youngest millennials are holding their own in terms of being engaged," he said.

3. People are most likely to volunteer for religious organizations.

A third of volunteers identified the main place they volunteer as a religious organization — more than any other type of group.

There are, however, large divides by age when it comes to where people volunteer. Among those 65 years of age and above, 42.7 percent said they volunteer primarily for a religious organization. But that figure is just 22 percent among those age 20-24 years, who were more likely to volunteer for an educational or youth service organization.

It's unclear what long-term effect this difference could have, Dietz said.

4. There are large socio-economic and racial differences in volunteer rates.

Those with a college education are by far the most likely to engage in volunteer service, the BLS report found.

Those with more education are also more likely to provide professional or management assistance or to tutor or teach, while those with less education are more likely to provide food or general labor.

When it comes to race, there are also significant differences, with whites most likely to volunteer.

"Education and income have a much larger impact than race and ethnicity," said Dietz.

Even after controlling for education and income, there are still racial differences, he said. This is probably due to a number of factors, he said, one of them being that some organizations are less likely to bring on minority teenagers as volunteers because they worry that they will be harder to hold accountable or keep under control than if they were paid.

But whatever racial gaps exist now are not consistent from year to year, Dietz said, and they do sometimes disappear.

Twitter: @allisonpond