Breaking from two decades of tradition, this year’s election exit poll is set to include surveys of voters in 31 states, not all 50 as it has for the past five presidential elections, according to multiple people involved in the planning.

Dan Merkle, director of elections for ABC News, and a member of the consortium that runs the exit poll, confirmed the shift Wednesday. The aim, he said, “is to still deliver a quality product in the most important states,” in the face of mounting survey costs.

The National Election Pool — a joint venture of the major television networks and The Associated Press — has not announced the states that won’t be included, but the decision is sure to cause some pain to election watchers across the country.