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The case for and against astrology
End of a shouting match

"If I doubt astrology to a believer, I am looked at with a shocked and bewildered stare, as if I were attacking apple pie and motherhood." Anthony Standen, Forget Your Sun Sign, 1977.

Abstract -- Eleven representative views of astrologers 1863-2006 imply that astrology is all-revealing, factual, inarguably true, applicable to everything including past lives, enthralling to thinkers, soon to dominate scientific thought, the key to a new world view, and more. Just study it seriously, they say, and you will be convinced it works. But seven representative views of scientists 1930-1998 who studied it seriously imply the exact opposite. This conflict of views can be explained by differences in what astrology means to different people, by differences in what astrology claims, and by the failure of astrologers to allow for non-astrological factors (hidden persuaders) that lead to astrology-like outcomes. The case against astrology is that it is untrue, it has failed hundreds of tests, and astrologers do not usefully agree on what a given birth chart indicates. The case for astrology is that a warm and sympathetic astrologer provides low-cost non-threatening therapy that is otherwise hard to come by. Much the same applies to sun sign astrology but at a more basic level. In short, there is more to astrology than being true or false. But astrology is an easy target for commercial abuse. It also faces strong competition from hundreds of self-help psychology books that it may or may not survive once its true nature becomes more widely known. Includes tests of validity and agreement, and insights into how not to test astrology.

End of a shouting match
Astrology has been a field made quarrelsome by a shortage of facts. Could astrology be true? Could the stars really correlate with human affairs? Such questions have been furiously debated without resolution for more than 2000 years. Astrology has been the world's longest shouting match.

Not any more. Advances in related areas (astronomy, psychology, statistics, research design) and a decisive technology (personal computers) have since 1975 put astrology under the scientific microscope like never before. Today, most questions can be answered. Quarrelling is no longer the option it once was. In what follows we ignore the usual tired arguments against astrology (sun signs do not agree with the constellations, there is no known way it could work) in favour of the only question that matters: What is the case for and against astrology?

Unfortunately the media generally see astrology only as a sales gimmick (eg sun signs in Sunday supplements) or as a source of sensation, as when phoneline astrologers earn huge sums or when crooked astrologers fleece the public. If your knowledge of astrology comes from what you read in the media, be aware that you are likely to be seriously misinformed both for and against astrology.

Views of astrologers
Astrologers leave you in no doubt that astrology works:

In short, astrology is all-revealing, factual, inarguably true, applicable to everything including past lives, enthralling to thinkers, soon to dominate scientific thought, the key to a new world view, and more. Just study it seriously and you will be convinced it works. Or so astrologers lead us to believe. Now a word from scientists who have studied it seriously.

Views of scientists
The following views reflect serious studies up to the 1990s:

Evidently astrology works if studied by astrologers but not if studied by scientists. How is such disagreement possible? To find out we must first look at what is meant by "astrology".

What is meant by "astrology"?
Astrology means different things to different people and leads to different levels of interest. In Western countries there are four broad levels of interest in astrology as shown below with the rough percentage of the population involved at each level. For comparison the proportion of people who are dentists is roughly 0.05%.

Level of interest
1. Superficial -- Reads sun signs, seeks entertainment, 50%
2. Some knowledge -- Has own chart, seeks self-examination, 2%
3. Deep involvement -- Calculates charts, seeks meaning to life, 0.02%
4. Scientific -- Performs tests, seeks answers, 0.00002%

On going through the levels there is a huge falling off in numbers and a dramatic change in what astrology means. At the first level are the readers of sun sign columns. They see astrology as entertainment. At the second level are those who have their birth chart calculated and read. They see astrology as an intriguing way of exploring themselves. At the third level are those who read charts to find meaning in their lives. They see astrology as a form of religion unconnected with the entertainment of sun sign columns. At the fourth level are those who test astrology scientifically. They see astrology as a popular belief worthy of study regardless of whether the belief is actually true.

The previous views of astrology by astrologers apply to levels 2 and 3, which also apply to people who consult astrologers. In the USA roughly one million people a year consult astrologers, which seems like a convincing vote in favour of levels 2 and 3. But even this number is only about 2% of the millions of Americans who at any one time are seeking answers to their psychological problems, and is less than 1% of those who read newspaper horoscopes. So the popularity of astrological consultations is perhaps no more remarkable than the popularity of any of 99 flavours of ice cream -- if it exists then some people will try it. Which of course does not explain why astrologers are convinced that astrology at levels 2 and 3 really works. For this we need to put astrology to the test.

Putting astrology to the test
Astrologers claim they can tell your character, abilities, health, love life, events, destiny, and more, just from your birth chart. It seems amazing that a handful of planets could show all this. Indeed, polls consistently show that many people don't believe it. But astrologers have the perfect answer -- just try it. Put astrology to the test, they say, and you'll be convinced it works. What could be more reasonable? So this is precisely what research has done.

Take sets of birth charts jumbled up with descriptions of their owners. Can astrologers match charts to owners? In astrology books they do it all the time. So we expect the proportion of successful matches to pile up close to 100%. To date a total of 54 studies have made this test using a total of 742 astrologers and 1407 birth charts. Despite these impressive numbers the average success rate was no different from the 50% expected by chance, see figure below. For these astrologers (many of them among the world's best) astrology performed no better than tossing a coin.

Astrologers fail to match charts to owners better than chance

Here the results expected by chance were determined by picking matches at random for each of the 54 studies and repeating 10,000 times. The difference between the 51.7% success rate achieved by astrologers and the 50.0% expected by chance is easily explained by the tendency of journals to accept positive results and reject negative results, and is in any case not even weakly significant (p=0.77).

For astrologers this is bad news, which they dismiss in various ways. They say the tests were unduly difficult or were run by people ignorant of astrology (in fact many were run by astrologers). They say you cannot test astrology (which if true would mean they could never know anything about it). Or they see the bad news as proof of astrology's subtlety, so it is right even when it is wrong (ditto). But once again research comes to the rescue with an ingenious test that avoids any need to match charts with owners.

How well do astrologers agree on what a given birth chart indicates? To date a total of 28 studies have put this to the test using a total of 559 astrologers and 762 birth charts. Typically each test looked at how well 5 to 30 astrologers agreed on what a given chart indicated about its owner. Their average agreement was dismal -- better than tossing a coin but nowhere near the minimum acceptable, see figure below. Again many of these astrologers were among the world's best.

Astrologers fail to usefully agree on what a chart means

In general no test of individuals is acceptable unless the agreement between practitioners or between applications is above 90% where chance agreement is 50%, that is, where first and second opinions agree better than chance in 4 out of 5 cases. However, if we are interested only in large differences rather than small ones, as in measuring blood pressure, then agreement down to 75% may be acceptable provided nothing better is available elsewhere. But anything below 70% is generally useless because first and second opinions will agree better than chance in less than 2 out of 5 cases. The average agreement among astrologers was 54.9%, or better than chance in barely 1 out of 10 cases.

The next question is obvious. If astrologers cannot usefully agree on what a birth chart indicates, how can they know that astrology works? Indeed, why should anyone bother with astrology in the first place? It is here that we need to ask what is meant by "astrology works".

What is meant by "astrology works"?
One of the key inspirations of recent research has been to recognise that astrology, however defined, delivers statements that (like statements generally) can contain (1) factual information such as "you have red hair", and (2) personal meaning such as "you are here to fulfil your destiny". As shown below, the distinction between facts and meaning helps to explain why astrology can be seen to work even when it doesn't.

At one extreme are people who seek only personal meaning. For them astrology works if it provides meaning. Here "it works" means "it is meaningful." This kind of astrology does not need to be true, and attacking it would be like attacking Superman comics or a religious faith. At the other extreme are people who seek only factual proof. For them astrology needs to be true. Here "it works" means "it delivers results beyond those explained by non-astrological factors", of which more later.

In between are people who see astrology as meaningful but grounded in the kind of factual statements ("Leos are generous") that fill astrology books. This allows research findings to be welcomed if positive ("it confirms astrology!") and rejected if negative ("astrology is not like that!"). But it does not end there.

How to convince yourself that astrology works
Linda Goodman says Leos are warm, generous, independent, and dislike being told what to do. So you ask one hundred Leos if this is true. Ninety say yes, the rest say it depends but generally yes. Cautiously you press on. Astrologers say a Mars-Neptune conjunction signifies a person who is idealistic and concerned with values such as consideration for others. So you ask one hundred people with a Mars-Neptune conjunction if they are idealistic. Ninety-five say yes.

Still cautious, you have your birth chart read. The astrologer tells you things she could not possibly have known, like you have a sense of humour and you sometimes worry about money. Amazingly, everything fits. You are now convinced that astrology works. You haven't the foggiest idea how it works but it certainly works. You conclude that disbelievers have no idea what they are talking about.

For astrologers that is the end of it. Millions of people have tested astrology in this way, and millions have ended up convinced that it works. For them this is end of story. Astrology really works! No doubt about it!

Why scientists are not convinced
But scientists are not convinced. They know we can be fooled into seeing faces in clouds by a whole host of non-astrological factors such as hidden persuaders (reasoning errors and statistical artifacts). They also know that the remedy is simple -- do what astrologers never do, namely use switched data as controls. So they put the same questions to non-Leos and people without a Mars-Neptune conjunction, and they have their chart read after giving the astrologer someone else's birth data.

The results confirm their suspicions. Whereas 90% of Leos said they were like Leo, so did 90% of non-Leos. Absence of a Mars-Neptune conjunction made no difference to people's idealism. And someone else's chart fitted them just as well as their own -- a point repeatedly confirmed by astrologers whenever they inadvertently use the wrong chart. Many tests with switched data have been made, always with results like these. Which of course is consistent with the studies shown earlier, where astrology performed no better than tossing a coin, and astrologers failed to usefully agree on what a given chart indicated.

For scientists that is the end of it, at least until the evidence indicates otherwise. Your sun sign and birth chart may fit you exactly but so do sun signs and birth charts not your own. Astrologers and clients cannot tell the difference. Like the Emperor's New Clothes, astrology seems to be built on self-deception. At which point the message is clear.

The message is clear
Before deciding whether or how astrology works we need to test switched data. We must stop asking if Leos are generous and ask instead if Leos are more generous than non-Leos. Without such comparisons our tests will be meaningless. But during twenty centuries astrologers have rarely tested switched data. So they cannot claim to know whether astrology works. If we bring together the evidence from hundreds of studies, and from articles elsewhere on this website, the case for and against astrology can be stated as follows. First the case against.

The case against astrology
The case against astrology is that it is untrue. It has not contributed to human knowledge, it claims the prestige of science without the methods of science, it has failed hundreds of tests, it does not deliver benefits beyond those produced by non-astrological factors (hidden persuaders), and users do not usefully agree on basics such as which zodiac to use or even on what a given birth chart indicates. No hint of these problems will be found in astrology books, which is why some scientists see astrologers as misguided or even fraudulent. In fact astrologers are mostly nice people who genuinely wish to help others.

But the claim that astrologers repeatedly make (astrology is true because based on experience) is simply mistaken -- what they see as its strength (experience) is actually its weakness (the experience is not assessed using switched data). They show little awareness of the factors such as the absence of accurate feedback that prevent learning from experience, or of the numerous hidden persuaders that give the illusion of such learning in its absence. Astrologers also show little interest in procedures that avoid the weaknesses of experience, and every interest in ignoring unwelcome evidence. Together these attitudes have created a case against that is longer and stronger than the case for.

The case for astrology
The case for astrology is that it is among the most enduring of human beliefs, it connects us with the cosmos and the totality of things, it provides a basic means of describing ourselves, and there is a wide range of approaches. In practical terms a warm and sympathetic astrologer provides low-cost non-threatening therapy that is otherwise hard to come by. You get emotional comfort, spiritual support, and interesting ideas to stimulate self-examination. And new ideas are always emerging that could raise spiritual awareness. In a dehumanised society an astrologer provides personal support at a very low price. Where else can you get this sort of thing these days?

Much the same applies to sun sign astrology but at a more basic level -- and many people seem to want it. Or as historian and social critic Theodore Roszak says in his book Why Astrology Endures (Briggs, San Francisco 1980): "For a growing number of people, the rich imagery of these old traditions has become a more inspirational way of talking [about ourselves] ... than conventional psychiatry. The astrological universe is, after all, the universe of Greco-Roman myth, of Dante, Chaucer, Shakespeare, Milton, Blake. It has poetry and philosophy built into it."

Conclusion
There is more to astrology than being true or false. But integrity and validity are crucial because astrology lends itself to commercial abuse, as in sun sign columns and phonelines, and to exploitation of the gullible. It also faces strong competition from thousands of self-help psychotherapy books that typically describe a problem and how to attack it, all supported by examples. Such books, especially if based on sound scientific principles, can help as much as psychotherapy does, see Clinical Psychology Review 13, 169-186, 1993. So it remains to be seen whether astrology can survive such competition once its own true nature becomes more widely known.

You can find more on tests of astrology in Research results, which gives abstracts for 91 studies typical of those made in the 1980s and 1990s, and in Meta-analyses, which gives overviews of all studies made in particular areas. Both articles are on this website under Doing Scientific Research.

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