Doctors are 15 percentage points more likely to order breast-cancer screening for patients they see first thing in the morning than they are right before lunch. Shown matching descriptions of hypothetical offenses, 208 federal judges differed by an average of more than 3.5 years in the length of the prison sentences they recommended. These professionals rarely realize how noisy their decisions are unless someone measures them. Investing is equally rife with unwanted and undetected variation. Read more at Wall Street Journal.