eivastausvääristymän

Eivastausvääristymä, also known as survivorship bias, is a logical error where one focuses on the people or things that made it past some selection process, and overlook those that did not, typically because of their lack of visibility. This can lead to false conclusions because the successful group is not representative of the entire group.

A classic example of survivorship bias involves the analysis of World War II bomber planes. When studying returning bombers to determine where to add more armor, statisticians initially focused on the bullet holes in the planes that came back. They observed that certain areas, like the fuselage and tail gunner positions, were heavily damaged. The initial conclusion was to reinforce these heavily damaged areas. However, Abraham Wald pointed out that this was a case of survivorship bias. The planes that returned were the ones that *survived* their missions. The areas that were *not* damaged on the returning planes were actually the critical areas. Planes hit in those locations likely did not return. Therefore, the armor should have been added to the areas that appeared undamaged on the surviving planes.

Survivorship bias can appear in many fields, including business, medicine, and finance. For instance, when studying successful companies, one might overlook the many companies that failed, leading to an overestimation of the ease of achieving success. Similarly, in medicine, focusing only on patients who recover from a disease might lead to an inaccurate understanding of the disease's typical progression or mortality rate. Recognizing and accounting for survivorship bias is crucial for making sound decisions based on data.