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Sachs's Astrology File
Sun sign best seller has fatal defects

Three critiques that appeared in 1998. Two are from Correlation 17(1), the third is from Skeptiker 11(3).

Gunter Sachs, The Astrology File: Scientific Proof of the Link Between Star Signs and Human Behaviour Orion Books, London 1998, translated from the original German version published in 1997.

Abstract -- The book is promoted on the cover as a "world-wide best seller". Its blurb says "At last the proof which answers the age-old question: Is there anything to astrology?" and "If you do believe in astrology, here's the proof. If you didn't believe in astrology, you will now". Here the first critique by astrologer Peter Niehenke shows how flaws in Sachs's reasoning make his results meaningless. Sachs tested occupations (47 groups), cause of death, criminals, suicides, and compatibility. His base samples were often very large (millions of cases) and were from diverse sources such as the Swiss census of 1990. For each test he corrected for demographic effects in the total population and then applied a statistical chi-squared test to the observed and expected sign totals. There were many significant differences, which he saw as proving the effect of sun signs. But his results are largely meaningless. Many factors influence the distribution of births including climate, culture, and social class, so there are many possible explanations for the observed differences, all more plausible than astrology. And if the sample is huge, as here, even the smallest effect will become statistically significant. Furthermore, Sachs never checked the large number of existing studies, which often found differences opposite to his own. In short, his observation of significant yet contradictory results is only to be expected and does not necessarily have anything to do with astrology. The second critique by psychologist Suitbert Ertel points out that all data is tabulated. So despite the flaws in reasoning (see first critique) the data can be re-analysed by improved methods. Factor analysis of the sun sign data for occupations revealed no similarities between similar occupations such as industrial economy and political economy, or medicine and veterinary medicine, or medicince and pharmacy. Nor was there any general ordering such as sciences vs humanities. A similar analysis of the sun sign data for criminal behaviour was equally negative. As for Sachs's data for 350,763 marriages, sun sign books say the compatibility between two signs is much the same regardless of which one is male or female. But when the liking of one sign for another was ranked for each male sign, and again for each female sign, the mean rank correlation between male and female rankings for all twelve signs was a negligible 0.05, not even weakly significant (p = 0.88). So the sun sign books are wrong. Nor was it any better when Sachs's divorces were analysed in the same way. There was no hint of the links expected if Sachs's results were genuinely due to astrology. This critique is a fascinating step-by-step look at how a sympathetic scientist applies powerful methods to astrological ideas, and at how good science sorts out bad science. Altogether the next best thing to doing the work yourself. The third critique by statistician Herbert Basler finds an abundance of statistical errors and is more suitable for technical readers. Most of the print-media reviews of Sachs's book were scathingly critical of how he interpreted his results. But most reviews seemed to agree that the calculations were correct, which is not the case. Sachs regularly makes mistakes, for example in the number of results said to be significant, using the wrong average to compute certain deviations, neglecting one tail of the statistical distribution (so his reported significance levels are inflated), miscalculating the statistics in his "simplified example" (which describes as nonsignificant a drug that cures 75% of cases, whereas if the illness were AIDS it would win a Nobel prize), using samples that differ from the comparison sample (there are 8.81% Pisces births but only 8.54% Pisces deaths, so 0.27% Pisces must be immortal, suggesting that statistics is something done by Zahlenfriedhofsgaertner, gardners who work in the cemeteries where dead numbers are buried), and wrongly assuming that the comparison data are stable (his sun sign births during 1925-60 differ from those during 1954-76). Such frequent errors would make us doubt Sachs's claims, even if everything else was acceptable (which, as the other critiques show, is not the case). Nevertheless Sachs's book does have one good point -- it contradicts the idea promoted by astrologers that astrology cannot be tested by statistical methods.