Republican U.S. presidential candidate and businessman Donald Trump pats former Florida Gov. Jeb Bush on the back during the second official Republican debate of the 2016 U.S. presidential campaign at the Ronald Reagan Presidential Library in Simi Valley, California, Sept. 16, 2015. Reuters

A shrinking roster of Republican presidential candidates will meet again during the third GOP debate of the primary season Oct. 28. The event, to be hosted by CNBC and the University of Colorado Boulder, will focus on the economy.

The qualifying criteria for the debate will likely result in a smaller field of candidates during the prime-time event. To qualify for the main stage, candidates must get at least 3 percent on average in national polls. A pre-debate forum will allow lower-tier candidates to fight for attention.

“To appear in the 8 p.m. debate a candidate must have an average of 3 percent among these polls,” CNBC announced in a statement, setting the main debate for 8 p.m. EDT Oct. 28. “Candidates who average below that will be invited to the 6 p.m. debate."

The top-tier candidates will likely include Donald Trump, Ben Carson, Carly Fiorina, Marco Rubio, Jeb Bush and Ted Cruz. It's unclear if John Kasich, Mike Huckabee, Chris Christie or Rand Paul will make the main event as they did in the previous two GOP debates. Bobby Jindal, Rick Santorum, George Pataki and Lindsey Graham are expected to remain on the pre-debate stage. CNBC will consider poll data from NBC, ABC, CBS, Fox, CNN and Bloomberg released between Sept. 17 and Oct. 21.

The debate, titled “Your Money, Your Vote: The Presidential Debate on the Economy,” will focus on jobs, taxes, the deficit and the health of the U.S. economy. “Presidential elections are often won or lost based on core economic positions, understandings and values,” said Mark Hoffman, CNBC chairman. “Our nation’s economy and place in the world, job growth, entrepreneurship and the pursuit of the American dream live at the very center of CNBC’s mission each day and will be the centerpiece of our line of focused questioning at this debate.”

Students will receive tickets to the event, making for a potentially younger crowd than usual. “We are delighted to host the first of the Republican presidential candidate debates to be held on a university campus,” said CU-Boulder Chancellor Philip P. DiStefano. “We appreciate the opportunity to partner with CNBC and feel this debate will be a memorable experience for our students and the entire community.”