7. Putting it to the Test

Of course, it isn’t necessary to know how something is supposed to work, in order to prove that it doesn’t. To test whether or not a hypothesis is correct, you carry out tests or experiments, and predict what the outcome should be, if the hypothesis is correct; then you check whether or not the observed outcome matches the predicted one.
Testing whether or not astrology works is very simple. If we start with the hypothesis that it has some validity, then we would expect any statistical test of its “predictive” abilities to achieve significantly better results than those which would be expected due to pure chance. ( Think of a multiple choice exam, in which each question has four possible answers. Even if you didn’t know any of the answers, you would expect to get 25% correct by random guessing. )
Many statistical tests of astrology have been carried out; not surprisingly, not a single one has ever shown any evidence that it works. I’ll describe some particularly good ones in Section 7.2 – but first, we’ll look at some studies of another kind.

7.1. If you want to believe...

Astrologers rely very heavily on the fact that those who want to “believe” will do, no matter what; they will accept just about anything in a horoscope or profile, as long as they believe that it was personally written for them. Numerous studies have been performed, which provide strong evidence that this is indeed the case. Most of the examples which follow are taken from an article which appeared in Sky and Telescope, the world’s foremost astronomy magazine, many years ago2.
The American illusionist James Randi is well known for exposing the trickery of so-called “psychics”, “clairvoyants” and people who claim to talk to the dead; he reproduces many of their “feats”, while never claiming to be anything but an illusionist. He has also done the same for astrology. He once visited a college, posing as an astrologer, and pretended to write personal horoscopes for each student in a class. He then asked them all to rate the accuracy of “their” horoscopes, and the majority claimed them to be accurate. Randi then told them to pass the horoscopes around, revealing that they were in fact all identical. The single horoscope had been written in the usual vague terms, such that those who wanted to “believe” could read into it whatever they liked.
Australian researcher Geoffrey Dean conducted a test using “real” astrological readings, which were done by an astrologer for a number of “believers”. Half of the subjects – the control group – were given their horoscopes as they were; for the other half, Dean “reversed” the horoscopes, substituting phrases which were the opposite of what the original said. Of those in the second group, just as many – 95% - claimed that the readings applied to them as those who had been given the “correct” readings!
But my favourite example is that of French researcher Michel Gauquelin in the 1980s. He got an astrologer to write the horoscope of a certain individual, then sent identical copies to 150 people, telling each one that it had been written for them, and again asked them to rate its accuracy. 94% of the subjects said they recognised themselves in the description. The actual subject of the horoscope was in fact – wait for it... one of France’s most infamous mass murderers!

7.2. Statistical tests

One of the commonest claims of astrology is that people of certain “star signs” are “compatible” with each other, and other combinations are not, with regard to romance and marriage. Psychologist Bernard Silverman put this to the test; he checked the “star signs” of nearly 3000 couples who were getting married, and over 400 who were getting divorced, against astrologers’ definitions of “compatible” and “incompatible” pairings. Not surprisingly, he found no correlation whatsoever; the statistics showed that supposedly “incompatible” couples get married just as often as “compatible” ones – and conversely, supposedly “compatible” couples get divorced just as often as “incompatible” ones.
Many astrologers also claim that a person’s “star sign” is correlated with their choice of profession; career advice is one of the worthless “services” offered by modern day astrologers. Physicist John McGervey looked at the biographies and birth dates of several thousand politicians and scientists, to see whether any particular “signs” dominated among those professions, as would be expected if the astrologers’ claims were correct. Once again, there was no correlation whatsoever; among both groups, people’s “signs” were distributed completely randomly.
Of course, “serious” astrologers claim that that there is far more to it than just a person’s “star sign”. Another physicist, Shawn Carlson, carried out an experiment which proved highly embarrassing to them. A group of volunteers were asked to provide all the personal information needed to cast their “full” horoscopes, and to complete a psychologists’ questionnaire, which used the same kind of general information.
A “respected” astrological group was asked to produce a horoscope for each subject. 28 other astrologers, who had agreed to take part, were then each sent a number of sets of data, each consisting of one horoscope and three of the psychological profiles, one of which belonged to the same person as the horoscope. Their task, in each case, was to interpret the horoscope and decide which of the profiles it matched – a one in three choice. In over 100 trials, their success rate was – wait for it... 34% - almost exactly what you would expect due to random guessing!
The aforementioned Geoffrey Dean, and psychologist Ivan Kelly, carried out a large-scale metastudy3 - a correlation of the results of several studies – and found that not one of them showed any results significantly different from pure chance. Some of these studies involved “time twins” – pairs of unrelated people who were born within a few minutes of each other and in the same city – and in many cases, just a few metres apart in the same hospital. ( Such pairs are not uncommon, as in a big city of a million people, at least a couple of hundred babies are born every day. Finding them is difficult, but not impossible; the researchers advertise in the media for volunteers, asking for people who were born in a given city and on one of a few specified dates. ) This should be the definitive test; if astrology had any basis at all, then such people would surely be expected to have very similar personalities. Needless to say, no such similarities were found.
Dean and Kelly’s paper can be read at www.imprint.co.uk/pdf/Dean.pdf.


2. Andrew Fraknoi, Your Astrology Defence Kit, Sky and Telescope, August 1989.
3. G. Dean and I. W. Kelly, Is Astrology Relevant to Consciousness and Psi?,
Journal of Consciousness Studies, 10, No. 6-7, 2003.

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