Category: Psychology

You don’t understand numbers

You are terrible with numbers, unless there is a very good reason why you are different from the subjects of the psychological experiments described below. See this post at the always interesting Overcoming Bias blog:

Then how about this? Yamagishi (1997) showed that subjects judged a disease as more dangerous when it was described as killing 1,286 people out of every 10,000, versus a disease that was 24.14% likely to be fatal. Apparently the mental image of a thousand dead bodies is much more alarming, compared to a single person who’s more likely to survive than not.

But wait, it gets worse.

Suppose an airport must decide whether to spend money to purchase some new equipment, while critics argue that the money should be spent on other aspects of airport safety. Slovic et. al. (2002) presented two groups of subjects with the arguments for and against purchasing the equipment, with a response scale ranging from 0 (would not support at all) to 20 (very strong support). One group saw the measure described as saving 150 lives. The other group saw the measure described as saving 98% of 150 lives. The hypothesis motivating the experiment was that saving 150 lives sounds vaguely good – is that a lot? a little? – while saving 98% of something is clearly very good because 98% is so close to the upper bound of the percentage scale. Lo and behold, saving 150 lives had mean support of 10.4, while saving 98% of 150 lives had mean support of 13.6.

Or consider the report of Denes-Raj and Epstein (1994): Subjects offered an opportunity to win $1 each time they randomly drew a red jelly bean from a bowl, often preferred to draw from a bowl with more red beans and a smaller proportion of red beans. E.g., 7 in 100 was preferred to 1 in 10.

According to Denes-Raj and Epstein, these subjects reported afterward that even though they knew the probabilities were against them, they felt they had a better chance when there were more red beans. This may sound crazy to you, oh Statistically Sophisticated Reader, but if you think more carefully you’ll realize that it makes perfect sense. A 7% probability versus 10% probability may be bad news, but it’s more than made up for by the increased number of red beans. It’s a worse probability, yes, but you’re still more likely to win, you see. You should meditate upon this thought until you attain enlightenment as to how the rest of the planet thinks about probability.

See full article for more examples and references.

In a follow-up article he has another great example. When subjects were asked to choose between a 7/36 chance of winning $9 or a 100% chance of winning $2, only 33% chose to go for the $9. That seems reasonable. But when (a different set of) subjects were asked to choose between these two choices:

Choice 1: 7/36 chance of winning $9 or a 29/36 chance of losing 5¢
Choice 2: 100% chance of winning $2

Strangely, 60.8% of the subjects chose choice 1! Note that this is strictly worse than the corresponding choice in the previous experiment. Apparently,

After all, $9 isn’t a very attractive amount of money, but $9/5¢ is an amazingly attractive win/loss ratio.

You can make a gamble more attractive by adding a strict loss to it! Isn’t psychology fun?

Again the full article contains even more goodies.

Why beautiful people have more daughters

The title of this post is the name of a book on “evolutionary psychology” written by two scientists trying to explain a lot of human behavior on the basis of evolutionary principles last seen in action during the stone age. This interview with one of the authors is rather interesting. The following excerpt explains the title of the book:

The basic idea is this: Whenever parents have genetic traits they can pass on to their children that are more valuable for boys than for girls, then they have more sons than daughters. Conversely, whenever parents have genetic traits they can pass on to their children that are more valuable for girls than for boys, then they have more daughters than sons. Physical attractiveness — being beautiful — is good for both boys and girls, but it’s much more advantageous for girls. Physical attractiveness of a woman is one of the most important considerations for men when they select both long-term and short-term mates, but a man’s physical attractiveness is important for women only when she’s looking for short-term mates. Women like to have affairs with good-looking men, but they don’t necessarily want to marry them, unless of course they are also rich and powerful.

So beautiful daughters will be more likely to take full advantage of their physical attractiveness than beautiful sons. Beautiful daughters are more likely to pass on their genes successfully to the next generation than beautiful sons, because they are more likely to find themselves in stable marriages to desirable spouses. In a representative sample of 3,000 young Americans, those who are “very attractive” had 36% greater odds of having a daughter compared to everyone else. Similarly, studies have found that big and tall parents are more likely to have sons, and short and thin parents are more likely to have daughters, because body size is more of an advantage to men than to women. Women are attracted to big and tall men much more than men are attracted to big and tall women.

See full article.

Resisting one temptation makes you vulnerable to another

Recent research suggests that:

As hu­mans, we have lim­it­ed re­sources to con­trol our­selves, re­search­ers say; all acts of con­trol draw from one source. So when us­ing this re­source in one do­main, such as di­et­ing, we’re more likely to run out of it in an­oth­er do­main, like stu­dy­ing hard.

Once these re­sources run out, our self-con­trol abil­ity is di­min­ished, ac­cord­ing to sci­ent­ists.

In an experiment, the scientists:

asked par­ti­ci­pants to sup­press their emo­tions while watch­ing an up­set­ting mov­ie. The idea was to de­plete their re­sources for self-con­trol. The par­ti­ci­pants re­ported their abil­ity to sup­press their feel­ings on a scale from one to nine. Then, they com­plet­ed a Stroop task, which in­volves nam­ing the col­or of printed words (i.e. say­ing red when read­ing the word “green” writ­ten in red), yet an­oth­er task that re­quires self-con­trol.

The re­search­ers found that those who sup­pressed their emo­tions per­formed worse on the task, in­di­cat­ing that they had used up their self-con­trol re­sources while hold­ing back their tears dur­ing the film.

See full article. Scott Adams has a humorous take on this that might amuse you.