Biased Thinking

By John Carr, NMA Massachusetts Activist

Confirmation bias: the tendency to selectively accept evidence that supports existing belief, while ignoring contrary evidence

Wishful thinking

We hear a lot about safety in debates over traffic rules. We like to think safety is on our side and safety wins any argument. Much of the time we’re fooling ourselves on both counts.

Do you believe in anthropogenic global warming? Odds are you do if you’re a liberal and you don’t if you’re a conservative. We seek facts that reinforce what we already believe. If you are anti-regulation and worry about the cost of new emissions standards, you prefer climate change to be unimportant. You notice the story about climate scientists deleting original temperature data. If you dislike cars, want Americans out of the Middle East, or are already spending carbon tax revenue in your head, you want a crisis. You notice it was the warmest December on record.

At least half of you are seeing what you want to see. Realistically, far more than half of the public chooses a favorite anecdote instead of digging deeper. One instance of fraud or one temperature record does not make either side right.

A man in my neighborhood didn’t want to have to look for a passing car before pulling out of his driveway in the morning. He and his neighbors made up a story of a plague of dangerous drivers almost killing school children. A study found there was one car per minute passing through. Allegedly nonexistent sidewalks did in fact exist. No safety problem.

Who cares? You don’t get on the Transportation Committee of the Board of Aldermen by being against traffic rules. They had already made up their minds. Residents’ complaints were accepted, the engineer’s report ignored, and through traffic banned. A traffic count found the ban didn’t work. Aldermen ordered a second traffic count with a police officer to ensure it got the right answer. The first count was ignored, the second count believed, and the ban declared a success.

Wishful thinking. They saw what they needed to see to convince themselves they were right.


Part of the problem is our desire to seek absolutes. Climate change is a myth or climate change will destroy the world and we must do anything to stop it. Nothing is wrong or all the children will die and we must do anything to save them. We are biased against overt cost-benefit analysis, so the absolute needs to be on our side.

What if rising sea levels will cause $5 trillion damage and preventing sea level rise will cost $10 trillion? Drown Florida, it’s not worth saving. What if saving 100 children cost $2 billion? Run over those kids; they aren’t worth $20 million each.

Yes, a life has measurable value. In America, it’s a million to a few million dollars. Multiply per capita GDP by lifespan and you’re in the ballpark. There are other ways to calculate value, including finding out how much extra pay people want for a risky job. They give similar answers.

I like explicit cost-benefit analysis. You get interesting results when you reduce apparently unrelated figures to common units like dollars. Judge Richard Posner has written extensively on the subject, and some of his books are worth reading.

Real motives

Most traffic rules are not really about safety. That by itself doesn’t make most traffic rules wrong. I’ll give an example of a good reason that isn’t about safety, and go into bad reasons another time.

One purpose of traffic control devices is to help people share the road. I’m talking plain English here, not bicycle slogan. If gaps in traffic come less often than once a minute, you might install a traffic signal to help pedestrians cross. If side street traffic backs up badly, all way stop signs or a roundabout can help both streets share equally. Drivers tend to understand and compliance is good. Don’t mistake these for safety devices. Stop signs and signals usually do not reduce crashes.

“An accident waiting to happen” sounds more compelling than “two minute wait at a stop sign.” Children at risk are more convincing than disliking the sound of a car driving past your house before you’ve had your morning coffee. If you’re like most people you can convince yourself even in the face of contradictory evidence. But most of the time lives are not at stake and we’re better off facing that fact.

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