To grasp why Standard Life agreed to buy Aberdeen Asset Management for £3.8bn this week, it helps to recall an experiment at the Oregon Research Institute in the 1960s, that rated how good doctors were at making judgments compared with formulas they helped to design.The models won, as Michael Lewis records in The Undoing Project, his book about the economics Nobel Prize-winning psychologist Daniel Kahneman and his late collaborator Amos Tversky. Not only did it cost less to use them to identify cancers and psychological disorders in patients than doctors, but they were more accurate.