Evidence based Astrology
Why Sun Signs are not suitable as tests for astrology
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Recently a sceptic claimed that there are hundreds of tests where astrology has failed. It is a popular view held by sceptics.

I challenged him to provide one solid and persuasive test that will back up his claim. I specified scientific tests rather than anecdotal tales, magic tricks, sun sign tests or tests with a sample size that is so small to enable random results

His best example was "The Love Signs study which looked at 27 million couples to see if astrology's predictions about 'compatibility' played out in the real world. They looked at conjunctions, sextiles, trines and of course sun signs and found none of the predictions made by astrology bore out. http://www.astrology-and-science.com/s-love2.htm There are literally hundreds more. Astrology is just so easy to study, which is why it's been studied so much."

So, his best example was a flawed test of sun sign astrology. I explained that sun sign astrology is a quasi-astrology originating from the 1930s that people read in the daily newspapers.

There are many problems with sun sign testing (which is based on the estimated sun sign from the date of birth only), besides the fact that it is not testing astrology. With this example the claims of sun sign compatibility come from sun sign columns and books. However, astrologers analyse compatibility by a series of factors and for example place more emphasis on Venus, Mars, the Moon, the Ascendant and other planets ahead of the Sun in this context.

One of the studies, the Gunther Sachs test (1999) claimed many significant findings based on sun sign data - however like most of these type of tests, it has serious sampling errors and needs a full re-analysis. It is not held up as evidence for astrology by astrologers and given the flaws should not be used by sceptics. Sun sign tests risk self-fulfilment and have to eliminate any direct questions from which the subject might guess were connected with his or her sign. This was an explanation for the extraordinarily significant results from the Mayo-Eysenck test (1978).

In fact, these tests aren't even accurate sun sign tests as the first and last day of each sign involves a changeover - so that without the time of birth, the sun sign is questionable. In addition, the changeover day varies from year to year and in my experience, these huge data studies do not take account of this. But at a minimum, one in seven couples have a suspect match, which in this study equates to 3.8 million people. At this stage most professional statisticians would have discarded this dirty data as a measure of sun signs. The tests showed a significant tendency for people to marry partners of the same sign or the adjacent sign. The post hoc analysis blames this embarrassing blip on recording error but by "excluding from same sign couples those with the same birthday or month of birth." they managed to smooth the data, so it is p=.08 which happens to be fractionally above statistical significance for this type of data at p=.05. If an astrologer cherry-picked the data in this way, there would be uproar.

What Dean neatly avoided and should have explained is that, as most astrologers and some astronomers know Venus is never more than 46.3 from the Sun on the ecliptic (as seen from Earth). This means that couples with the same or adjoining signs are likely to have Venus conjunct their partner's Sun, Venus or Mercury. Now if you look at any textbook on astrology (not a Sun Sign column), you will find that for over two thousand years the planet Venus (and not the Sun) was and is associated with love.

It should be obvious to anyone familiar with astrology that Dean is selective in presenting his data. He is after all part of the CSI (ex CSICOP) machine that is financed by publications that promote the beliefs of uncritical followers (most of whom are not real scientists). I don't disagree with their views on all subjects, but with astrology, they have used their extensive funds to (inadvertently) provide more 'proof' than 'disproof'! So, I say bless them! Citing sun sign studies as arguments against astrology is a classic straw man argument. Dean cites Russell Grant and Mystic Meg who are easy targets and media entertainment personalities. It's rather like using an agony aunt column to debunk the entire field of psychology.

So, are you saying sun signs should be removed from astrology completely? Because if they have any impact at all then that impact can be tested. It's as if I said, "Tall people tend to have more knee problems." We all know there are other factors that influence whether someone has knee problems (level of exercise, diet, genetics, etc) and that not all tall people will have knee problems. But that doesn't take away the fact that if we tested a bunch of tall people versus average height people and found neither group had more knee problems than the other then the statement "tall people have more knee problems" would be falsified. Claims made for sun signs are like that.

You actually cited Dean's interpretation (unpublished outside the web) of 3 sun sign studies of which only one was published in a peer reviewed journal, Correlation and this study showed significant correlations between sun signs. So, your best study from the claimed hundreds is one that appears to support astrology even at the sun sign level. Even so, it's not a study that I would cite in this page as I have superior and relevant studies that support astrology using the whole chart.

Isolated use of sun signs is a recent (1930) popular phenomenon and was never part of traditional astrology (from ca.5000 BCE) and not part of mainstream astrology. It's not that the sun sign is meaningless; it's just that it works better within the chart. With your medical example, it would be like extracting the patient's heart and wondering why it wasn't beating like it did inside the body. This analogy is by way of explanation rather than a literal argument.

Misquoting sun sign astrologers about sun signs is not relevant to mainstream astrology and continually using the known limitations of sun sign astrology as a straw man argument gives the impression that your insistence that astrology is a pseudoscience (like many other sceptics) is based on a fundamental misconception of astrology.


Robert Currey

Sachs, Gunter (1999) The Astrology File: Scientific Proof of the Link Between Star Signs and Human Behaviour. Orion Books
www.twitter.com/RobertCurrey
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