Abraham Wald

Abraham Wald was a Hungarian-American mathematician and statistician who founded the field of sequential analysis, a framework for statistical hypothesis testing in which data is evaluated as it is collected and a decision to stop and reach a conclusion can be reached before a predetermined sample size is met. Wald also laid foundational work in statistical decision theory, developing a general mathematical framework for choosing among possible actions under uncertainty by minimizing the maximum possible loss, an approach that influenced both statistics and economics. During the Second World War, working with the Statistical Research Group at Columbia University, Wald analyzed the pattern of damage found on Allied bomber aircraft that returned safely from missions, in order to recommend where to add armor; his key insight was that the missing data mattered most, since the visible damage on returning planes showed locations a plane could be hit and still survive, while planes hit in the truly vital, unobserved locations did not return at all, a foundational illustration of what is now called survivorship bias. Wald emigrated to the United States in 1938 after facing antisemitic restrictions on his academic career in Austria, and he spent his career at Columbia University until his death in a plane crash in India in 1950 while on a lecture tour.