NASHVILLE, TN - Nashville is one of the strongest metropolitan economies in America, according to a new study that looked at nearly two dozen factors over 20 years. POLICOM recently released its yearly community "economic strength" rankings, and Nashville came in at 4th in the country.

That's six spots higher than the area's 2016 and 2017 ranking. POLICOM ranked all 383 metropolitan statistical areas as well as all 550 micropolitan statistical areas, which refers to smaller economies. Here's how other metropolitan cities in Tennessee ranked:

Knoxville (73)

Memphis (136)

Chattanooga (143) Here's how other micropolitan cities in Tennessee ranked: Cookeville (31)

Shelbyville (33)

Sevierville (68) For the second consecutive year, Austin, Texas, topped the list for metropolitan areas.

"With a diversified economy, the area has enjoyed consistent economic growth for a very long time," the company said in a release. Bozeman, Montana, jumped up a spot from last year to take the top spot for micropolitan areas, as a result of what the company said was rapid growth in professional services and manufacturing.

"The top rated areas have had rapid, consistent growth in both size and quality for an extended period of time," company President William Fruth said in a release.

POLICOM, based in Palm City, Florida, studies local and state economies and gives them advice on how they can improve. While the rankings reflect how an area has behaved, it doesn't necessarily indicate why it has behaved that way. Individual communities each have their own economic characteristics and can grow — or decline — for a myriad of reasons. Even so, a local economy's growth and expansion is directly tied to the amount of money flowing into the area, Fruth said.

"For the most part, money is imported to a community by way of the business activity of the primary or contributory industries," he said. "These enterprises sell their goods or services outside the area, thus importing wealth to the economy."The strongest economies have "nurtured and caused" their main businesses to grow and expand, Fruth said. In the weakest areas, the main businesses failed, causing the overall economy to dip. The company used data from 1997 to 2016 for its latest study.A metropolitan area must be at least one county and have a city with at least 50,000 residents.