Survival bias: Abraham Wald’s intuition


The survival bias, a term invented by Oscar Wirld, often arises at the basis of fallacious reasoning frequent in analysis and discourses. Let’s find out the origin ot this term

Where the term survival bias originates?

In 1942, a group of scientists from Columbia University in New York launched a series of analyzes and studies to support the activities of the army at the request of the American government. Among the members of the research team was Abraham Wald, a forty-year-old Hungarian mathematician of Jewish descent. Wald identified a logical error termed survival bias. Analyzing the bullet holes on the fuselages of the aircraft returned after the missions, the military initially thought they had to add protections in the most damaged points. Wald thought otherwise. The undamaged spots were precisely the ones to be protected. That because they indicated that the planes hit in those spots had evidently been shot down by the opposing forces and had never returned to base. 

What is the survival bias?

Survival bias is an error that occurs when in evaluating a situation one focuses only on the people or things that have passed a certain selection process. While neglects all the other elements because of their own invisibility. It underlies common fallacious reasoning in analysis and discourse concerning disparate human disciplines and activities. It can lead to extremely misleading conclusions 

The Abraham Wald’s discovery

What Wald did was identify a particular type of defect in the dataset, now conventionally described as survival bias. The planes that could be analyzed did not provide examples of where planes were hit most frequently. Wald’s work is today considered fundamental for the contribution he made to the birth of operations research. Also for the methods and mathematical models useful for predicting the behavior of these systems and identifying the decisions that optimize performance 

The post-pandemic reading increase

An example of survival bias

If three of the five best-graded students at the university come from the same high school, a survival bias could lead one to believe that that high school offers excellent education. But in the absence of other data, the reality may well be that that high school is only a very large school. In addition, in the most common and everyday speeches there is often a survival prejudice even in the statement according to which things are no longer done as they once did 


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