Democratic nominee for D.C. mayor Muriel Bowser; independent mayoral candidate David Catania. (Melina Mara; Sarah L. Voisin/The Washington Post)

A new poll finds Democrat Muriel E. Bowser with a double-digit lead over independent David A. Catania with 15 days left in the D.C. mayoral race.

Bowser carried 45 percent support among likely D.C. voters, with Catania holding 33 percent support and fellow independent Carol Schwartz with 12 percent. Only 7 percent said they were undecided.

The survey was commissioned by Economic Growth D.C., a pro-business advocacy group, and reached 800 likely voters via landlines and cellphones between Thursday and Sunday. It was performed by Greenberg Quinlan Rosner Research, a prominent Democratic polling firm, and carries a margin of error of plus or minus 3.5 points.

Economic Growth D.C. commissioned the last published poll of the mayor’s race, which found an 8-point margin between Bowser and Catania in late September.

Like the previous poll, the new Economic Growth D.C. poll selects respondents from a voter list rather than by dialing random numbers, as in most media polls. In the late September survey, 53 percent of likely voters were white, while 42 percent were African American. In the new poll, 48 percent of likely voters are black and 43 percent white — hewing more closely to the demographic split seen in the mid-September NBC4/Washington Post/Marist poll that put Bowser 17 points ahead of Catania.

The earlier poll showed 27 percent undecided, while the new poll shows 7 percent undecided. “It seems that Democrats who may have been on the fence have come home to council member Bowser,” said Dave Oberting, Economic Growth D.C.’s executive director. “Any momentum that Catania might have had seems to have been blunted.”

Still, a memo prepared by the polling firm identified “an element of fluidity left in the race” despite Bowser’s lead: “One-in-five voters in this electorate are weak Bowser supporters, and another 7 percent remain undecided. Further, as the following table shows, Bowser’s advantages on key images all fall short of her overall 12-point lead on the ballot.”

On two of those “images” — “Will improve the economy and create jobs in the District”; “Represents people like me” — Bowser holds a significant advantage over Catania. On the other hand, voters asked who “will work with the business community to grow and create jobs” and who “represents a change from the current administration” give Catania an advantage. On the questions of who “will reduce crime and drugs” and who “will improve public schools,” Bowser and Catania are statistically tied.

Peyton M. Craighill contributed to this post.