Astrology doesn't work. Many careful tests have now shown that, despite their claims, astrologers really can't predict anything.After all, we don't need to know how something works to see whether it works. During the last two decades, while astrologers have somehow always been a little too busy to conduct statistically valid tests of their work, physical and social scientists have done it for them. Let's consider a few representative studies.Psychologist Bernard Silverman of Michigan State University looked at the birth dates of 2,978 couples who were getting married and 478 who were getting divorced in the state of Michigan. Most astrologers claim they can at least predict which astrological signs will be compatible or incompatible when it comes to personal relationships. Silverman compared such predictions to the actual records and found no correlations. For example "incompatibly signed" men and women got married as frequently as "compatibly signed" ones.Many astrologers insist that a person's Sun sign is strongly correlated with his or her choice of profession. Indeed, job counseling is an important function of modern astrology. Physicist John McGervey at Case Western Reserve University looked at biographies and birth dates of some 6,000 politicians and 17,000 scientists to see if members of these professions would cluster among certain signs, as astrologers predict. He found the signs of both groups to be distributed completely at random.=09To overcome the objections of astrologers who feel that the Sun sign alone is not enough for a reading, physicist Shawn Carlson of the Lawrence Berkeley Laboratory carried out an ingenious experiment. Groups of volunteers were asked to provide information necessary for casting a full horoscope and to fill out the California Personality Inventory, a standard psychologists' questionnaire that uses just the sorts of broad, general, descriptive terms astrologers use.A "respected" astrological organization constructed horoscopes for the volunteers, and 28 professional astrologers who had approved the procedure in advance were each sent one horoscope and three personality profiles, one of which belonged to the subject of the horoscope. Their task was to interpret the horoscope and select which of the three profiles it matched.Although the astrologers had predicted that they would score better than 50 percent correct, their actual score in 116 trials was only 34 percent correct - just what you would expect by guessing! Carlson published his results in the December 5, 1985, issue of Nature, much to the embarrassment of the astrological community.Other tests show that it hardly matters what a horoscope says, as long as the subject feels the interpretations were done for him or her personally. A few years ago French statistician Michel Gauquelin sent the horoscope for one of the worst mass murderers in French history to 150 people and asked how well it fit them. Ninety-four percent of the subjects said they recognized themselves in the description.Geoffrey Dean, an Australian researcher who has conducted extensive tests of astrology, reversed the astrological readings of 22 subjects, substituting phrases that were the opposite of what the horoscopes actually stated. Yet the subjects in this study said the readings applied to them just as often (95 percent of the time) as people to whom the correct phrases were given. Apparently, those who seek out astrologers just want guidance, any guidance.Some time ago astronomers Culver and Ianna tracked the published predictions of well-known astrologers and astrological organizations for five years. Out of more than 3,000 specific predictions (including many about politicians, film stars, and other famous people), only about 10 percent came to pass. Veteran reporters - and probably many people who read or watch the news - could do a good deal better by educated guessing.If the stars lead astrologers to incorrect predictions 9 times out of 10, they hardly seem like reliable guides for decisions of life and affairs of state. We must speak out whenever it is useful or appropriate - to discuss the shortcomings of astrology and the shaky ground it is based on.