Friday the 13th in science

posted by @ulaulaman about #superstitions #friday13th #mathematics #economics #socialscience
Men would never be superstitious, if they could govern all their circumstances by set rules, or if they were always favoured by fortune: but being frequently driven into straits where rules are useless, and being often kept fluctuating pitiably between hope and fear by the uncertainty of fortune’s greedily coveted favours, they are consequently, for the most part, very prone to credulity.
Benedict de Spinoza, A Theologico-Political Treatise, Preface Part 1.
In Italy 13 is considered a lucky number, so the unlucky day for us is Friday the 17th, but in the last decades also Friday the 13th becames an unlucky day. Following wiki.en, the origin of this superstition is unknown: the earliest evidence about it is referred in the biografy of Gioacchino Rossini written by Henry Sutherland Edwards in 1869: indeed Rossini died on a Friday 13th
He [Rossini] was surrounded to the last by admiring friends; and if it be true that, like so many Italians, he regarded Fridays as an unlucky day and thirteen as an unlucky number, it is remarkable that one Friday 13th of November he died.
Now, from an economical point of view, could be interesting the following abstract:
The Friday the 13th anomaly of Kolb and Rodriguez (1987) is revisited in an international context. Drawing on the philosophy of science approach of Lakatos (1978), the paper argues the importance of “anomalies” and the need for triangulation. Using the FTSE world indices over 1988–2000 for 19 countries, it is found that there is some evidence that returns on Friday the 13th are statistically different from, and generally greater than, returns on other Fridays.(1, 2)
Lucey's results seem a confirmation of the results of another work by Andrew Coutts:
In recent years much evidence has been documented of the existence of regularities in security price returns. However, one of the least investigated anomalies concerns the socalled ‘Friday the 13th’ effect, where returns on Fridays which fall on the 13th of the month display significantly lower returns than other Fridays. Employing daily logarithmic returns from the Financial Times Industrial Ordinary Shares Index (FT 30) for the period July 1935 through December 1994, we find no evidence of a Friday the 13th effect. Indeed, if anything, we find returns are higher on Friday the 13th than on other Fridays. We then partition the sample into six subsamples each of ten years, again concluding that there is no evidence of a Friday the 13th effect, and that once again returns on Friday the 13th tend to be higher than on other Fridays. Finally, we conclude that our results support the extremely limited evidence documented for the UK market concerning the Friday the 13th effect.
So the ancient superstitions could have an influence also in our advanced society:
Although superstition is a common phenomenon in our modern society, only a few studies have explored empirically on what it depends. This paper investigates the factors which determine superstition, reporting some preliminary empirical results. The findings indicate that socio-demographic and socio-economic conditions matter. There seems to be a certain concurrence between churches and superstitious beliefs, the correlation between superstition and attendance of church and other religious activities being mostly negative. On the other hand, an overall greater religiosity increases superstition. The results also indicate that there is a strong variance in superstition in different countries. People from formerly Communist countries show a particularly high degree of superstition. It could therefore be concluded that superstition substituted the religious beliefs and activities eradicated during the Communist era.(4)
The most funniest papers, in particular for the conclusions in their abstracts, are about the influence of Friday the 13th on the city traffic:
OBJECTIVE: This study compared deaths from traffic accidents on Friday the 13th with those on other Fridays in a national population.
METHOD: The author examined the daily deaths from traffic accidents by sex and age and the mean daily temperature in Finland, 1971–1997. Adjusted risk ratios for death on Friday the 13th versus other Fridays were obtained by negative binomial regression.
RESULTS: In men, the adjusted risk ratio for dying on Friday the 13th, compared with other Fridays, was 1.02, but for women, it was 1.63. An estimated 38% of traffic deaths involving women on this day were attributable to Friday the 13th itself.
CONCLUSIONS: Friday the 13th may be a dangerous day for women, largely because of anxiety from superstition. The risk of traffic deaths on this date could be reduced by one-third, although the absolute gain would remain very small: only one death per 5 million person-days(5).
OBJECTIVE: To examine the relation between health, behaviour, and superstition surrounding Friday 13th in the United Kingdom.
DESIGN: Retrospective study of paired data comparing driving and shopping patterns and accidents.
SUBJECTS: Drivers, shoppers, and residents.
SETTING: South West Thames region.
MAIN OUTCOME MEASURES: Numbers of vehicles on motorways; numbers of shoppers in supermarkets; and hospital admissions due to accidents.
RESULTS: There were consistently and significantly fewer vehicles on the southern section of the M25 on Friday the 13th compared with Friday the 6th. The numbers of shoppers were not significantly different on the two days. Admissions due to transport accidents were significantly increased on Friday 13th (total 65 v 45; p < 0.05).
CONCLUSIONS: Friday 13th is unlucky for some. The risk of hospital admission as a result of a transport accident may be increased by as much as 52%. Staying at home is recommended.(6)
But the most incredible results come from mathematics: the 13th Day of the Month Is More Likely to Be a Friday than Any Other Day of the Week(7, 8)!

(1) Lucey B.M. (2000). Friday the 13th and the philosophical basis of financial economics, Journal of Economics and Finance, 24 (3) 294-301. DOI:
(2) Lucey B.M. (2001). Friday the 13th: international evidence, Applied Economics Letters, 8 (9) 577-579. DOI: (pdf)
(3) Coutts J.A. (1999). Friday the thirteenth and the Financial Times Industrial Ordinary Shares Index 1935-94, Applied Economics Letters, 6 (1) 35-37. DOI:
(4) Torgler B. (2007). Determinants of superstition, The Journal of Socio-Economics, 36 (5) 713-733. DOI: (pdf)
(5) Nayha S. Traffic Deaths and Superstition on Friday the 13th, American Journal of Psychiatry, 159 (12) 2110-2111. DOI:
(6) Scanlon T.J., Luben R.N., Scanlon F.L. & Singleton N. (1993). Is Friday the 13th bad for your health?, BMJ (Clinical research ed.), 307 (6919) 1584-1586. PMID:
(7) Baxter S.R. (1969). To Prove That the 13th Day of the Month Is More Likely to Be a Friday than Any Other Day of the Week, The Mathematical Gazette, 53 (384) 127-129. DOI: (pdf)
(8) Irwin J.O. (1971). Friday 13th, The Mathematical Gazette, 55 (394) 412-415. DOI: (pdf)

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