Research of Astrology

Astrology has repeatedly failed to demonstrate its effectiveness in numerous controlled studies. Effect size studies in astrology conclude that the mean accuracy of astrological predictions is no greater than what is expected by chance, and astrology's perceived performance has disappeared on critical inspection. When testing for cognitive, behavioral, physical and other variables, one study of astrological "time twins" showed that human characteristics are not molded by the influence of the Sun, Moon and planets at the time of birth. Skeptics of astrology also suggest that the perceived accuracy of astrological interpretations and descriptions of one's personality can be accounted for by the fact that people tend to exaggerate positive 'hits' and overlook whatever does not fit, especially when vague language is used. They also argue that statistical research is often wrongly seen as evidence for astrology due to uncontrolled artifacts. A large-scale study, with a sample size of about 15,000 "astro-twins", was published in 2006. It examined the relationship between date of birth and individual differences in personality and general intelligence, and found no evidence that a connection existed. It also found no relationship between the zodiacal signs and participants' personal traits.

French psychologist and statistician Michel Gauquelin claimed to have found correlations between some planetary positions and certain human traits such as vocations. Gauquelin's most widely known claim is known as the Mars effect, which is said to demonstrate a correlation between the planet Mars occupying certain positions in the sky more often at the birth of eminent sports champions than at the birth of ordinary people. A similar claim is made by Richard Tarnas in his work Cosmos and Psyche, in which he explores correspondences between planetary alignments and historically significant events and individuals.

Since its original publication in 1955, the Mars effect has been the subject of critical studies and skeptical publications which refute it, and studies in fringe journals claiming to support or expand the original claims. Gauquelin's research has not received mainstream scientific notice.

The Forer effect is seen in astrology when most people simply accept their horoscopes as custom even if, by logic, it would mean that 1/12 of the world would have the exact same day or week.