Headlines From Psychology, Part 2

Here’s part 2. (And if you missed it, here’s part 1.) Again, if you are either interested or skeptical, leave me a comment and I’ll point you to the evidence.

Statistically, Divorce is Not a Good Strategy for Getting a Better Marriage: 50 to 67% of first marriages end in divorce. 60 to 77% of second marriages end in divorce.

Your Brain Has Trouble Giving Information About Probabilities Due Weight, So Pay Attention to Base Rates: We have trouble taking the actual prevalence of events into account when making decisions. For example, people tend to be more afraid of dying in a plane crash (lifetime chance: 1 in 20,000) than dying in a car wreck (lifetime chance: 1 in 100) or even of a heart attack (lifetime chance: 1 in 5). One reason for this is that we confuse the ease with which we can think of an example to be an indication of how likely something is. Try this: What do you think is more common, words beginning with “r” or words with “r” as the third letter?

If You Test Positive For a Very Rare Disease, You Still Probably Do Not Have That Disease: This is a headline that should come from medicine, not psychology, but psychologists are better at probability than doctors, who are no better than laypeople, at least when it comes to thinking about this: Even with a very accurate test, if a disease is very rare, a positive result is still much more likely to be a false positive than an accurate positive. I’m going to explain this, but if you don’t get it, don’t worry. Just remember the headline. It’s true.

The table below shows a hypothetical situation with super-round numbers to make it easier to get. You have gotten positive results on a test that is 99% accurate for a disease that occurs only once in 10,000 people. Most people figure they are 99% likely to have the disease. They are wrong:


Test Results
Disease Present? Test Results Positive Test Results Negative Row Totals
Disease Present 99 1 100
Disease Not Present 9,999 989,901 999,900
Column Totals 10,098 989,902 1,000,000

Since your test results are positive, you are somewhere in the left-hand column. You are either one of the 99 who both have the disease and whose test results are positive, called “hits,” or one of the 9,999 who do not have the disease but whose test results are positive, called “false positives.” As you may see, even though your test results are positive, you still are 99% likely to be a false positive and not a hit, simply because the disease is so rare.

Yes, this is counter-intuitive. That’s why it’s important. And that’s why statistics are important. Again, if you don’t understand, don’t worry. If you don’t believe it, though, come up with a specific question, leave it as a comment, and I’ll answer it.

If You Need Help, Ask Someone Specific for Something Specific: Bystanders generally do not help people who are in trouble. The bigger the crowd, the less likely someone will help. It’s not because they are bad or lazy. It’s a specific kind of well-documented confusion. Kind of like in the clip below. What you need to know is, if you need help, even if it seems like it should be completely obvious to anyone around, like you’re having a heart attack, falling to the ground, gasping, whatever, point to a specific person and give them specific instructions: “You, in the red shirt. I’m having a heart attack. Call an ambulance.” Do not assume anything will happen that you did not specifically ask for. A corollary of this headline is, if you think someone might be in trouble, don’t assume they would ask you for help, and don’t assume someone else is helping them. Help them yourself. It could mean the difference between them living or dying.

Get Help For Your Marriage When the Trouble Starts (Or Before): On average, couples wait 6 years after their marriage is in trouble to get help. The average marriages last 7 years. That means that most people who come to couples counseling are deeply entrenched in problems that would have been relatively easy to resolve earlier. It is not uncommon for a couple to come in to counseling with a covert agenda to use the counselor to make their inevitable divorce easier. We can do this, but believe me we’d much rather meet you earlier and help you stay together! Also, I’m not joking about “or before.” Couples counselors are well-trained to give “tune-ups” to couples who are doing well. It’s a good idea.

Anger Is Not Destructive of Relationships, Contempt and Defensiveness Are: Everybody argues. Everybody screws up their communications. It’s the ability to repair things that is the key, and contempt and defensiveness get in the way of that.

[First published on Nathen’s Miraculous Escape, January 24, 2010.]