Astrology Debunked - Again

Star signs predict well-being about as well as random numbers

A new paper in the journal Kyklos finds no reliable associations between people’s star signs and their happiness, health, work satisfaction, financial satisfaction, or marital happiness.

Drawing on data from 12,791 participants in the General Social Survey, the paper found that star signs explain less than 0.3% of the variance in people’s responses. To be fair, 0.3% isn’t 0%. However, the paper also found that if you randomly assign people a number from 1 to 12, those numbers “explain” just as much of the variance as the star signs. This suggests that the explained variance is really just random wobble, and that actually star signs explain nothing at all.

Needless to say, these aren’t the first findings to challenge the predictive power of astrology. There are many other examples, some as amusing as they are enlightening.

One of my favorites comes from Christian Rudder, co-founder of the dating website OKCupid. Rudder analyzed data from 500,000 users to see if their star signs predicted who they matched with. Nope! Star signs had zero effect on how compatible people were.

Another example comes from the mathematician and entrepreneur Spencer Greenberg, who compared the predictive power of zodiac signs to that of the Big 5 personality traits for 37 important life outcomes. You can read about the findings here and here, but the basic message is captured nicely in the following graph.

Here’s an excerpt from an open-access astronomy textbook, discussing various other empirical tests of astrology.

In a fine example of such a test, two statisticians examined the reenlistment records of the United States Marine Corps. We suspect you will agree that it takes a certain kind of personality not only to enlist, but also to reenlist in the Marines. If sun signs can predict strong personality traits - as astrologers claim - then those who reenlisted (with similar personalities) should have been distributed preferentially in those one or few signs that matched the personality of someone who loves being a Marine. However, the reenlisted were distributed randomly among all the signs.

More sophisticated studies have also been done, involving full horoscopes calculated for thousands of individuals. The results of all these studies are also negative: none of the systems of astrology has been shown to be at all effective in connecting astrological aspects to personality, success, or finding the right person to love.

Other tests show that it hardly seems to matter what a horoscope interpretation says, as long as it is vague enough, and as long as each subject feels it was prepared personally just for him or her. The French statistician Michel Gauquelin, for example, sent the horoscope interpretation for one of the worst mass murderers in history to 150 people, but told each recipient that it was a “reading” prepared exclusively for him or her. Ninety-four percent of the readers said they recognized themselves in the interpretation of the mass murderer’s horoscope.

Geoffrey Dean, an Australian researcher, reversed the astrological readings of 22 subjects, substituting phrases that were the opposite of what the horoscope actually said. Yet, his subjects said that the resulting readings applied to them just as often (95%) as the people to whom the original phrases were given.

This video shows the magician and skeptic James Randi conducting a similar experiment.

None of these findings should be surprising, of course; there’s no reason at all to think that star signs would predict anything other than people’s answer to the question “What’s your star sign?” Still, it’s good to have decent data to help persuade the undecided that astrology is simply bunk.

And if they’re still not persuaded, perhaps xkdc’s economic argument against astrology and other pseudoscientific beliefs will finally tip the scales…

• You can access a free copy of the star-signs-and-wellbeing paper here.

• Follow Steve on Twitter/X.

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