In the early 1980s, Paul Sackett, a psychologist at the University of Minnesota, began measuring the speed of cashiers at supermarkets. Workers were told to scan a few dozen items as quickly as possible while a scientist timed them. Not surprisingly, some cashiers were much faster than others.
But Mr. Sackett realized that this assessment, which lasted just a few minutes, wasn’t the only way to measure cashier performance. Electronic scanners, then new in supermarkets, could automatically record the pace of cashiers for long stretches of time. After analyzing this data, it once again became clear that levels of productivity varied greatly.