The American middle class isn't shrinking, but it continues to fall further behind upper-income households financially, research shows.

About half (52%) of American adults lived in middle-class households in 2016, according to Pew research, but income disparity has increased between the middle class and wealthier class.

According a recent Brookings Institution report that examines where the middle class lives, the presence of the middle class varies considerably across U.S. metro areas. National policies aimed at improving the conditions of the middle class, and helping people rise to join it, will impact metropolitan areas differently. Therefore, the report concludes, interventions like the Earned Income Tax Credit or Medicaid can have important local implications.

Local economic factors can shape the size of the middle class. These include the types of industries and the jobs available, education and skills of workers, and access to transportation, housing and education, according to Brookings.

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So where does the middle class live? And where don't they live?

Because salaries and cost of living vary geographically, for the purpose of the study, the report defines middle-class as U.S. households with incomes between about $25,000 and $120,000 in 2017, then adjusts them based on regional price parities and average household size.

The study examined data from 382 metro areas to determine the share of households that were low, middle, and high income.

Here are the 15 places with the largest share of middle class, and the 15 with the smallest share of middle class.