Research and consultancy firm NPD Group found that a third of customers who bought breakfast foods at lunch or dinner hadn't ordered from McDonald's at all before the launch of all-day breakfast on Oct. 6.

Breakfast food orders rose to 47 percent of McDonald's total orders after the launch, from 39 percent before, according to NPD's analysis, which used a database of more than 27,000 McDonald's receipts.

All-day breakfast was launched nationwide on Oct. 6, and was heralded by observers as a shot in the arm to a company coming off years of sluggish sales. Weeks after the launch, McDonald's said all-day breakfast was driving momentum in a sales turnaround. Some franchisees complained the launch complicated their food preparation, was slowing order times and in some cases was leading customers to choose cheaper breakfast items over pricier sandwiches.

But McDonald's CEO Steve Easterbrook said last month that it was actually leading customers to buy more per visit, a point the NPD confirmed. The study showed that average purchases went up during lunch hours, the chain's busiest time of day, as customers combined breakfast and lunch items in a single order.

McDonald's, in data shared with the Tribune last week, said that one in four people are grabbing fries with their breakfast items, and about 20 percent are ordering hash browns as a side at lunch.