When such claims are made there must be some data to back them up.

"Must be"? According to whom? Even more importantly, which data is relevant here? And beyond that, whose data would satisfy whom - if anyone?

There have been only a handful of scientific studies done on astrology to date, bobad, as pointed out several times already on this thread.    ANd most of the results have been negative. Take a look - I posted a great link called "astrology and science" a few days ago, with a few such articles and studies for your perusal.

But don't go lighting those self-congratulatory cigars just yet -- I repeat, all scientific studies done on astrology to date are next to useless, as they are either based on a false premise (ie 'testing' for astrology's alleged 'predictiveness'), or using methods/techniques insufficient to even identify, never mind differentiate / assess the relative importance of the seemingly endless number of astrological variables mapped out in a natal chart.