Michel Gauquelin and his wife Francois are French researchers who studied over 20,000horoscopes using scientific methods to try to test the validity of astrology. While they did not find evidence for astrology as it is generally practiced, they did find statisical proof of a relationship between the planets and personality.
They studied people who were extremely successful in their occupation, and those who were considered average. Those who were extremely successful were found to have planets in common more often than if by chance.
Their findings may be limited because they only studied 10 occupations. They found the Moon, Venus, Mars, Jupiter, or Saturn occupying 4 specific areas in the horoscope chart to be significant at the time of birth. The two areas of the chart they found most important roughly correspond to the ascendant and midheaven areas of a chart using Placidus houses. The two less important, but still significant, areas are in the area of the descendant and the IC.
Gauqelin says that only planets in those specific positions in a birthchart will manifest and the traits of planets in those positions will manifest exactly. However, the way these traits are used will depend on each person's condition in life, environmental factors such as family, education, community, social status, and even luck.
The Gauqelins also found hereditary astrological factors. They say that if a parent has one of the above mentioned planets in one of the important areas in their charts there will be a tendency for their children to be born with that planet in one of the significant areas.