The Bureau of Labor Statistics (BLS) is out with its most recent ranking of the 20 fastest-growing occupations in the U.S.. Coming in at #1, with median pay of $83,580 a year and a growth rate of 53 percent between now and 2022: "Industrial-organizational psychologists." What the heck is that?

Whatever it is, its growth rate beats that of every other occupation, including personal care aids (49 percent), home health aides (48 percent), diagnostic medical sonographers (46 percent), stonemasons (43 percent), stone masons laying down "segmented paving stones" (38 percent) and the members of 14 other fast-growing occupations.

The Society for Industrial and Organizational Psychology says its members are versatile scientists "specializing in human behavior in the workplace." Employers hire them—either in-house or as consultants—because their expertise results in better hires, increased productivity, reduced turnover, and lower labor costs.

Says the BLS, "Industrial-organizational psychologists [I-O psychologists] apply psychology to the workplace by using psychological principles and research methods to solve problems and improve the quality of work life. They study issues such as workplace productivity, management or employee working styles and employee morale. They also work with management on matters such as policy planning, employee screening or training and organizational development."

In short, you hire I-O psychs to improve the efficiency of your organization. Unlike many other kinds of consultants you might hire, they can show causality between their contribution and improved performance of your business.

Henry Kasper, the BLS supervisor who tracks this occupation, tells ABC News that it's one of the smallest that BLS follows: There are maybe 1,600 such psychologists. Though their job growth is indeed forecast to be robust, total growth between now and 2022 is only 900 jobs.

Nonetheless, says Kasper, "Companies see they can get a lot of benefit from hiring them (I-O psychologists) on a contract basis. They come in and help improve productivity. The trend is up—and in a pretty significant way. Given it's so small, you don't need to add that many jobs to get a massive percentage increase."

Tracy Kantrowitz, an I-O psychologist and director of RD for consulting firm SHL, says she wasn't surprised by BLS's ranking her profession #1. "It's consistent with what we've seen in recent years," she tells ABC News. "Applications to grad schools are way up." A masters degree in psychology or a doctorate are important--if not essential--prerequisites to getting hired, she says.

A number of other fast-growing occupations, as defined by BLS, require no degree and involve far bigger numbers of workers. Personal care aides and home health aides will be needed to care for the ever-swelling tide of aging Baby Boomers. Diagnostic medical sonographers will be in demand because the technology of sonography is advancing rapidly: it provides a way to look inside the body without subjecting it to radiation, as with X-rays.

Certain building trades jobs will advance as that industry recovers, and because these jobs enjoy special advantages within the trade. Segmental pavers will be in demand, says BLS's Kasper, because prefabricated, interlocking paving stones present a cheaper alternative to concrete.

Herewith, the top 20 fastest-growing occupations between now and 2022, as defined by BLS: