Gauquelin seems to have been the author for most of the studies mentioned, so I will point out the problems with those studies.

There are problems with Gauquelin's methodology. First of all he used the wrong numbers in some of the statistics (using N for number of traits rather than number of subjects) which inflated the findings. Using the correct statistics diminished the effects by a great deal. Secondly, he didn't use a blind procedure - the trait extraction was done by Gauquelin AFTER her knew the positions of the planets. He therefore could have unconsciuosly affected the results. From the astrology and science website: "Gauquelin accepted that a Gauquelin extraction bias had "very likely ... played a role in the [personality] studies", because computer checks of his manual results had confirmed the presence of Gauquelin bias in his sector calculations. But the calculation bias affected his results only slightly, so he felt it was "unlikely ... that [extraction] bias in the studies explains 100% of the results" (Correlation 10(2), 22, 1990). But biassing the translating of trait words (where there is always a range of English words for each French one) is easier than biassing the sector corresponding to a given birth time (where only a small proportion will be ambiguous). And in this case it needed only 1 in 12 translated traits to be biassed to produce the mean observed effect size of 0.10. So Gauquelin could be 11/12ths or 92% unbiassed, at first sight a level not worthy of suspicion, yet enough bias would remain to explain his results."

A replication was done by Ertel (1990) which avoided extraction bias, and no significant effect was found.

There are also apparently problems with older data caused by parents providing birth data and there was evidence that parents faked birth data to suit prevailing beliefs - the effects seem to disappear with newer data when the data is supplied by hospital records.

Astrologers seem very keen to quote those gauquelin studies which found effects, but never seem to mention his negative results...