Research

The Mars effect: relative frequency of the diurnal position of Mars in the birth chart of eminent athletes.

Studies have repeatedly failed to demonstrate statistically significant relationships between astrological predictions and operationally-defined outcomes.

Effect size studies in astrology conclude that the mean accuracy of astrological predictions is no greater than what is expected by chance.

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.

Researchers 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.