Report on Astrology-Schizophrenia Study

Introduction

On 22 March 2022, Pumpkin Person posted on my behalf a solicitation for volunteers to complete a survey where they ranked supposed personality descriptions of people born under astrological zodiac signs by their similarity to the imagined personality of someone experiencing Schneider’s first-rank symptoms of schizophrenia. Thank you, PP! The survey is no longer available, but if I gain access to a sufficiently large and properly responding sample of volunteers, I might reopen it or study this hypothesis again with a different method. Note that the volunteers were not informed that these personality descriptions were borrowed from astrology, nor what the survey was intended to study, although I expect that at least some of them figured those out.

I doubt that the alignment of celestial bodies causally influences individual differences in human temperament, but could the stargazers have gotten something right by coincidence? This study was intended to test my hypothesis that astrological knowledge might reflect nascent, semi-conscious knowledge of the fact that a person’s risk of eventually developing schizophrenia varies based on their month of birth. Statistical studies have found that this risk follows an approximately sinusoidal curve with a period of one year. Compared to the baseline of June, relative risk ranges from about 1.1 in February and March to 0.85 in August and September, a difference of about 30% between peak and trough. [1] This is thought to be caused by maternal vitamin D deficiency due to lack of sunlight in the coldest months, and perhaps also by prenatal exposure to certain seasonal infections. [2] [3]

Methodology

My first task was to define my null and alternative hypotheses:

H0: There is no positive relationship between: (1) the similarity of characteristic symptoms of schizophrenia to supposed personality traits of an individual born under a zodiac sign; (2) the risk that someone born under that sign will eventually develop schizophrenia.

H1: There is a positive relationship between (1) and (2).

From there, I mapped out the following research program:

  1. Rank zodiac signs by schizophrenia risk: starting with Pisces, since it most overlaps the highest-risk month of March; and ending with Virgo, which most overlaps the lowest-risk month of September. Note that each zodiac sign partially overlaps two months, so I determined schizophrenia risk for each sign by consulting Figure 1 in [1] for the schizophrenia risk of the month with which that sign shares the most days, e.g., Capricorn spans from December 21 to January 20, so it’s linked to January. This shift should be too small to affect the overall results much. A problem is that I couldn’t always discern the slight differences in Figure 1, the source I was using for this ranking. I decided on the following ordering, from highest to lowest expected risk, and did so before receiving any survey responses so as to prevent researcher bias: Pisces, Aquarius, Capricorn, Taurus, Aries, Sagittarius, Gemini, Scorpio, Cancer, Libra, Leo, Virgo.
  2. Present volunteers with: (1) a description of Schneider’s first-rank symptoms of schizophrenia; (2) descriptions of supposed personality traits of persons born under certain zodiac signs, all from the same source which was not created for the purpose of this study, and without selectively presenting only some of those traits. For this source, I chose [4]. Ask volunteers to rank those personality descriptions from greatest to least resemblance to the schizophrenia symptoms. Personality descriptions are presented in a random order for each participant, to reduce possible bias from order, e.g., less-attentive respondents tending to give lower numbers to options which appear earlier.
  3. Calculate each zodiac sign’s schizophrenia rating as the average rank of schizophrenia resemblance which volunteers assigned to it, from 1 (highest) to 12 (lowest).
  4. Calculate the rank-order correlation between zodiac signs’ schizophrenia risks from step 1 and volunteer-rated schizophrenia similarity ratings of zodiac signs from steps 2 and 3.
  5. Calculate a p-value for the correlation found in step 4. Because the alternative hypothesis H1 seems unlikely, not to mention that any research pertaining to astrology will have to overcome especial skepticism, the significance threshold was set beforehand at (p < 0.01), well below the usual (p < 0.05). Incidentally, I advocate for (p < 0.000001) to become the standard significance threshold in academia, but under the presumption that professional academics are, or should be, more able to recruit a large and high-quality sample than is an independent amateur researcher such as myself, so I did not hold myself to that standard here.

Results

My prior concerns, expressed in the previous sentence, about poor quality and quantity of responses were vindicated. While about 60 people started the survey, only 10 completed it, and of these: 5 responded as instructed; 4 gave faulty responses by leaving one or more ratings blank and/or assigning the same ranking to multiple personality descriptions; and 1 was an obvious troll, whose ‘name’ was a racial slur and who assigned the same ranking to every description. This atrocious audience engagement may reflect that the survey required substantial reading, totaling about 1700 words for the instructions, schizophrenia symptoms, and personality descriptions, as well as laborious judgment to rank every sign. If I repeat this experiment, I will almost certainly do so with a shorter and easier survey.

Because these data were so exiguous and suspect, I calculated the rank-order correlation, as discussed in step 4 under Methodology, for each of several different amalgamations of the responses. First, I calculated it with only the 5 fully correct responses. Then, I calculated it again, including the 4 faulty responses by interpolating missing rankings and reassigning reused rankings with a random number generator. In each case, if there was one or more tie(s) in the month rankings, I calculated the rank-order correlation for each possible tiebreak, e.g., if Capricorn and Aquarius were tied, I would calculate it once with Capricorn above Aquarius and once with Aquarius above Capricorn.

None of these rank-order correlations were remotely significant even at p < 0.05, and a fortiori not significant at p < 0.01. Ah well. You win some, you lose some, and I lost this one; at least, perhaps, until I try again with a better sample.

Intriguingly, Pisces and Aquarius were consistently ranked among the most schizophrenic signs, and Virgo among the least, all of which concord with my hypothesis. However, this is only one of practically infinitely many possible post hoc pseudo-confirmations, each of which could have happened by sheer chance, and thus it cannot be considered strong statistical evidence.

Because this study was a failure, this report’s purpose is more to present the hypothesis than the results I found. I call it a failure because of the deficient data, not because of the null result, as, from a proper scientific perspective, a null result is a success if the null hypothesis is true.

Additional Note

Different sources give slightly different tabulations of schizophrenia risk by birth month, but there is apparent agreement that risk is highest near the beginning of the year when the weather is coldest, and lowest about three-quarters of the way through the year when the weather is warmest. Would this reverse in the Southern Hemisphere, relative to the Northern?

References

[1] Effects of Family History and Place and Season of Birth on the Risk of Schizophrenia
(See Figure 1.)

[2] Seasonality and infectious disease in schizophrenia: the birth hypothesis revisited
(This study found that winter birth month predicted higher schizophrenia risk, but that rates of influenza and measles did not, which by exclusion supports the hypothesis that the causal factor here is vitamin D deficiency.)

[3] Season of Birth – Low Sunlight Exposure/Vitamin D deficiency is associated with higher risk of schizophrenia

[4] Your guide to all 12 zodiac signs: Dates, symbols, compatibility (I mildly edited these descriptions to shorten them and make it less obvious that they were drawn from astrology. This source is one of many which I could have used.)

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