Skip to main content

Verified by Psychology Today

Cognitive Dissonance

Are Your Blind Spots Derailing Your Decisions?

“Our very eyes are sometimes, like our judgments, blind.” –Cymbeline

Key points

  • Survivorship bias is focusing on positive information while neglecting negative data, which may be of equal or greater importance.
  • The reasons for failures may provide greater insight than the reasons for successes.
  • Survivorship bias may be thought of as failure to check one's blind spots.

During World War II, the Allied forces sought ways to minimize the loss of bombers and their crews to anti-aircraft fire. They commissioned a study of planes that took hits and were still able to return safely to base. It seemed plausible that armoring the most frequently hit areas on these planes would reduce crashes from strafing. (Armoring the entire surface area of planes was not an option, as this made them too heavy.)

A group of experts at Columbia University was commissioned to study the problem. Abraham Wald, a statistician working on the project, realized that focusing on data from safely-returned bombers was exactly the wrong approach. Instead, the Allies should focus on those areas of planes that, when hit, caused them to crash. The returning planes typically showed hits to the wings and tail. But none of the returning planes sustained serious damage to the engines or cockpit. Bombers hit in those areas crashed and were lost. So the armor should be applied to the areas not damaged on the returning planes.

Wald’s study of World War II aircraft is the origin of the term “survivorship bias”—erroneously focusing on the areas of planes that remained serviceable when damaged while disregarding the areas that failed under fire. Today the term is usually defined as making decisions based only on positive information while disregarding negative data, which may be just as important or even more so.

Once you know the story of Abraham Wald and the World War II bombers, the term “survivorship bias” is quite understandable. However, I think “blind spot bias” is a better term. People know what a blind spot is whether or not they are familiar with the Abraham Wald story.

A Case of Blind Spot or Survivorship Bias

When I was a full-time professor, students would occasionally drop by my office to discuss some multi-level marketing (MLM) scheme that had recruited them. They claimed to want my advice, but when I gave it to them, they would usually argue with me and launch into their memorized talking points.

One such student remains especially memorable. He had signed on with a travel-related MLM. I had not heard of this company before, so as he described in rapturous tones the riches he expected to make, I Googled the company. I showed him that they had a “D” rating with the Better Business Bureau. I also showed him page after page of complaints from both disillusioned sales representatives and from dissatisfied customers. This evidence made no impression on him. Instead, he attempted to recruit me into this MLM before I cut him off. A couple of weeks later, he dropped out of college to become a full-time salesman for this MLM—but not before alienating most of his classmates by pressuring them to join.

This is a textbook example of a fatal blind spot—i.e., survivorship bias. This student allowed himself to be lured by the siren song of this MLM based on the alleged success of a few insiders at the top of this pyramid scheme. Yet he willfully disregarded substantial evidence of failed salespeople, ruined friendships, strained marriages and relationships, and financial disaster.

Other Examples

The self-help book, The 7 Habits of Highly Effective People, became a best-seller. The title implies that practicing these seven habits can help make you a highly effective person. Nevermind that the definition of “highly effective” is likely to vary from person to person. Failing to consider the many thousands of people who have practiced these habits and yet have not become “highly effective” (whatever that means) would be a blind spot or survivorship bias.

A reasonable question might be: Did “highly effective” people get that way because of these habits, in spite of these habits, or were these habits of no effect one way or the other? Were the habits the cause, or were they merely correlated?

A university where I formerly taught wanted to improve “student success”—which is academic speak for students who stay in school, pass their courses, and graduate. The university wanted to minimize drop-outs and fail-outs. So they began collecting data on students who were doing well and making progress.

Much like The 7 Habits of Highly Effective People, the university sought to help at-risk students by mentoring them on how to be more like successful students (e.g., better study habits, improved note-taking, etc.). That approach made only trivial improvements in student success outcomes. What it mostly did was postpone students’ dropping out or failing academically. The university’s blind spot or survivorship bias was in failing to concentrate its investigation on the characteristics of students who dropped out or failed their courses. Then the school could have supported these students with a food pantry (if hunger was an issue), with need-based scholarships (if financial distress was an issue), and so on.

Subaru advertises that 96% of all its vehicles sold in the past 10 years are still on the road, and they assert that this is a better percentage than Toyota or Honda. This may be true, and it may be due entirely to the quality of Subaru vehicles. However, if we accept this claim at face value, what is/are our blind spot(s)?

Notice that Toyota and Honda are mentioned, but other makes of vehicles are not. Are there car companies with results equal to or better than Subaru? Why didn’t they say that no company can match Subaru's 96% record if that is true? Might Subaru’s 96% ratio be attributable to the safe driving habits and regular maintenance practices of people who tend to buy Subarus more than to the quality of the vehicles? Could other makes and models be more susceptible to theft and other types of loss? Are other brands of cars more likely to be purchased by younger or less safe drivers, thereby driving down the ratios of those brands compared to Subaru's 96%? You may not be able to discover answers to such questions, but before being swayed by an advertised assertion, it is wise to consider such possibilities. At least you will know you haven't neglected your blind spots.

“Ignorance is the root of misfortune.” –Plato

© Dale Hartley. Connect with me on social media.

More from Psychology Today

More from Dale Hartley MBA, Ph.D.

More from Psychology Today