For the August debate, Ipsos conducted a poll commissioned by the Washington Post and FiveThirtyEight to ask who the winner of the debate was, among Republican primary voters and debate watchers. Here are the details on the results and methodology for the first debate: https://www.washingtonpost.com/documents/840f8cf6-85c3-4dda-b5b8-6734f8317ff0.pdf?itid=lk_inline_manual_2

This market is in anticipation of a similar poll for the September 27th debate. The question that will resolve this market is "No matter how you plan to vote, who do you think performed best in the Republican primary debate on Wednesday?", which is Q4 in the August debate poll.

If Ipsos does not conduct a poll for the debate, I'll use the most similar question of the first poll released by a similar pollster (e.g., Emerson, Leger, or a similar reputable pollster).