Astrology
Effectiveness

Astrology has not demonstrated its effectiveness in controlled studies and has no scientific validity. Where it has made falsifiable predictions under controlled conditions, they have been falsified. One famous experiment included 28 astrologers who were asked to match over a hundred natal charts to psychological profiles generated by the California Psychological Inventory (CPI) questionnaire. The double-blind experimental protocol used in this study was agreed upon by a group of physicists and a group of astrologers nominated by the National Council for Geocosmic Research, who advised the experimenters, helped ensure that the test was fair and helped draw the central proposition of natal astrology to be tested. They also chose 26 out of the 28 astrologers for the tests (two more volunteered afterwards). The study, published in Nature in 1985, found that predictions based on natal astrology were no better than chance, and that the testing "...clearly refutes the astrological hypothesis."

In 1955, the astrologer and psychologist Michel Gauquelin stated that though he had failed to find evidence that supported indicators like zodiacal signs and planetary aspects in astrology, he did find positive correlations between the diurnal positions of some planets and success in professions that astrology traditionally associates with those planets. The best-known of Gauquelin's findings is based on the positions of Mars in the natal charts of successful athletes and became known as the Mars effect. A study conducted by seven French scientists attempted to replicate the claim, but found no statistical evidence. They attributed the effect to selective bias on Gauquelin's part, accusing him of attempting to persuade them to add or delete names from their study.

Geoffrey Dean has suggested that the effect may be caused by self-reporting of birth dates by parents rather than any issue with the study by Gauquelin. The suggestion is that a small subset of the parents may have had changed birth times to be consistent with better astrological charts for a related profession. The number of births under astrologically undesirable conditions was also lower, indicating that parents choose dates and times to suit their beliefs. The sample group was taken from a time where belief in astrology was more common. Gauquelin had failed to find the Mars effect in more recent populations, where a nurse or doctor recorded the birth information.

Dean, a scientist and former astrologer, and psychologist Ivan Kelly conducted a large scale scientific test that involved more than one hundred cognitive, behavioural, physical, and other variables—but found no support for astrology. Furthermore, a meta-analysis pooled 40 studies that involved 700 astrologers and over 1,000 birth charts. Ten of the tests—which involved 300 participants—had the astrologers pick the correct chart interpretation out of a number of others that were not the astrologically correct chart interpretation (usually three to five others). When date and other obvious clues were removed, no significant results suggested there was any preferred chart.
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