Oh wow, they really were comparing Kit-Kat & Mars bars as an "economic-value-based food-choice task". If the scientists' criteria was economic, why were subject

Oh wow, they really were comparing Kit-Kat & Mars bars as an "economic-value-based food-choice task". If the scientists' criteria was economic, why were subjects asked "which of two food items they would prefer to eat at the end of the experiment"? And then they call this decision "Willingness To Pay", even though the subjects receive the chocolate for free. Maybe we should just strip this back to actual facts. Scientists observed that subjects in a trial typically spent 250ms longer choosing between a free KitKat & Mars bar (that they may receive after the experiment), than they did on choosing between two groups of random dots on a screen.