Short Report

Season of Birth Contributes to Variation in UniversityExamination Outcomes

MARTIN FIEDER,1,2* HERMANN PROSSINGER,2 KAROLINE IBER,1 KATRIN SCHAEFER,2

BERNARD WALLNER,2 AND SUSANNE HUBER3

1Rector’s Office, University of Vienna, A-1010 Vienna, Austria2Department of Anthropology, University of Vienna, A-1090 Vienna, Austria3Research Institute of Wildlife Ecology, University of Veterinary Medicine of Vienna, A-1160 Vienna, Austria

ABSTRACT Epidemiological studies show that birth season influences a wide range ofbiological parameters such as growth, reproduction, mental illnesses, dyslexia, personality, andsuccess in school. The present study is aimed at examining birth season’s relationship to exami-nation marks achieved at a university in a very large contemporary sample of male and femaleundergraduate students. We find that female university students born in spring and summerachieve better marks than those born in autumn and winter. Male students born in springreceive worse marks than those born in other seasons of the year. Furthermore, we find a birth-week periodicity in examination results of female students, with highest examination resultsfor those born in May. We suppose that biological mechanisms might explain part of theobserved effects. Am. J. Hum. Biol. 18:714–717, 2006. ' 2006 Wiley-Liss, Inc.

Epidemiological studies show that birth sea-son influences a wide range of biological pa-rameters such as growth (Weber et al., 1998),reproduction (Huber et al., 2004a,b), mentalillness (Castrogiovanni et al., 1998), dyslexia(Livingston et al., 1993), personality (Chotaiet al., 2001), and success in school and in sci-ence (Bell and Massey, 1994), and fluctuatingasymmetry in humans (Benderlioglu and Nel-son, 2004). For children, the claimed relation-ship between birth season and school perform-ance has been attributed to the peculiarity ofthe school system (Williams et al., 1970). InAustria, for instance, children born in summerare at a disadvantage because they are theyoungest in their school age cohort, compris-ing children born in September–August. Sea-son-of-birth effects on examination perform-ance in adults, however, must (if they doindeed exist) have other causes, as age-basedseason-of-birth influences vanish by age 12years (Hutchinson and Sharp, 1999). Theirputative existence may shed light on veryearly neuronal and cognitive development.

SUBJECTS AND METHODS

To investigate the influence of birth seasonon examination marks, we used the (anony-mous) examination results from 1995–2001 ofundergraduate students at the University ofVienna, together with their dates of birth. We

included only examinations of those studentswho had taken more than five examinations. Inthis large data base (947,662 examinations of33,036 female students, and 411,642 examina-tions of 16,397 male students), we looked for apossible association between examinationmarks received by male and female students,separately, with their birth dates. The medianage of students at time of examination was22.75 years (quartiles: 25%, 20.92 years; 75%,25.67 years). The examinations covered a widerange of disciplines taught in various faculties:theology (0.9%), economics (8.8%), social sciences(33.9%), humanities (27.7%), natural sciencesand mathematics (20.6%), and others (8.0%).

In the Austrian university system, examina-tion scores are encoded on a five-grade scalefrom ‘‘sehr gut’’ (‘‘excellent,’’ encoded here as ‘‘5’’)to ‘‘nicht genugend’’ (‘‘failure,’’ encoded here as‘‘1’’). Our procedure was as follows. 1) We com-

Grant sponsor: Austrian Program for Advanced Research andTechnology, Austrian Academy of Sciences; Grant sponsor: Aus-trian Science Fund; Grant number: P18089-B03.

*Correspondence to: Dr. Martin Fieder, Rector’s Office,University of Vienna, Dr. Karl Lueger Ring 1, A-1010Vienna, Austria. E-mail: martin.fieder@univie.ac.at

Received 21 March 2006; Accepted 22 March 2006

Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ajhb.20539

Martin Fieder and Hermann Prossinger contributed equallyto this work.

AMERICAN JOURNAL OF HUMAN BIOLOGY 18:714–717 (2006)

VVC 2006 Wiley-Liss, Inc.

pared the distribution of scores separately formale and female students born in the four sea-sons (winter, December 21–March 20; spring,March 21–June 20; summer, June 21–Septem-ber 22; autumn, September 23–December 20),using cross-tabs (overall w2 testing as well as w2

post hoc testing between groups, Bonferroni-corrected). 2) We searched for any periodicity inthe time series of the average examination scoresper week of birth for all male and female stu-dents born in 1967–1977 who took these exami-nations. We eliminated trends in the data usinglinear regression of the average scores per birthweek, and computed a Lomb-Scargle periodo-gram (Press et al., 1992) of this time series tofind significant periods. We calculated the peri-odic signal using the Fourier components thatwere found to be significant by Lomb-Scargleperiodogram. 3) We performed a multiple re-gression analysis with yearly averages of exami-nation scores of all (male and female) studentsas dependent variable, and year of birth andyear of study as independent variables, to assessthe effects of age cohort and study year on exam-ination performance. 4) Finally, we tested therelationship between photoperiod (at the lati-tude of Vienna, 48.128 North) and average ex-amination scores for each birth week, separatelyfor all male and all female students born in1967–1977, to analyze whether perinatal photo-period might be involved in the underlyingphysiological mechanisms of any found birth-season effect.

RESULTS

The distribution of scores attained by maleand female students is associated with theirbirth season (see data in Table 1). Mean scoresattained by females born in autumn were sig-nificantly lower than those by females born inother seasons of the year. Additionally, female

students born in autumn received, on average,the highest score ‘‘excellent’’ less frequentlythan those born in other seasons of the year(chi-square test: overall w2 ¼ 47.74, P < 0.0001;winter-spring, ns; winter-summer, ns; winter-autumn, w2 ¼ 31.29, P < 0.0001; spring-summer,ns; spring-autumn, w2 ¼ 33.50, P < 0.0001;summer-autumn, w2 ¼ 25.55, P < 0.001). Amongmales, mean scores attained by studentsborn in winter and summer were significantlyhigher than those by students born in springand autumn. Male students born in winter andsummer received the highest score ‘‘excellent’’more frequently than those born in springand autumn (chi-square test: overall w2 ¼ 43.78,P< 0.0001; winter-spring, w2¼ 23.12, P< 0.0001;winter-summer, ns; winter-autumn, w2 ¼ 16.74,P¼ 0.002; spring-summer, w2¼ 21.70, P< 0.001;spring-autumn, ns; summer-autumn, w2 ¼ 17.60,P ¼ 0.001). Overall, the birth-season patternof received scores (mean examination scores,and proportion of the highest score) is differ-ent in both sexes, with autumn-born femalesand autumn- and spring-born males receiving,on average, the lowest scores.In the male sample, we did not find any sig-

nificant period in the Lomb-Scargle periodo-gram. This lack of significance is most likelydue to the higher overall variance and lowersample size of examination scores in malecompared to female students (males: variance¼ 1.78, average ¼ 36.110; females: variance ¼1.66, average ¼ 36.408). For females, theLomb-Scargle periodogram showed a signifi-cant peak (P � 0.01) at a period of 52 weeks;thus, the Fourier component has a 1-yearcycle (Fig. 1). We observed that the linearregression shows a decrease in examinationperformance for the younger female students.We can attribute this observation to twoeffects: 1) the examinations for the younger

TABLE 1. Data and statistical estimators of examination scores1

Female students Male students

Winter Spring Summer Autumn Winter Spring Summer Autumn

Excellent (%) 33.07 33.14 33.08 32.48 34.58 34.06 34.45 33.87Good (%) 27.75 27.63 27.56 27.68 25.45 25.13 25.53 25.40Satisfactory (%) 18.87 18.96 18.95 19.28 18.04 18.11 18.14 18.18Passing (%) 11.23 11.18 11.29 11.52 11.69 11.92 11.47 11.97Failure (%) 9.08 9.08 9.11 9.05 10.24 10.77 10.41 10.58Mean mark 3.6449 3.6457 3.6422 3.6303 3.6245 3.5979 3.6215 3.6001Standard error 0.0026 0.0026 0.0027 0.0027 0.0042 0.0041 0.0041 0.0043Median age (years) 22.71 22.47 22.42 22.66 23.81 23.50 23.45 23.60N (examinations) 238,229.0 250,390.0 234,128.0 224,915.0 102,404.0 107,515.0 106,286.0 95,437.0

1Distribution of scores awarded (percentage), mean score, standard error, median age of students, and sample size (N) for birth sea-sons, separately for females and males taking examinations.

715BIRTH SEASON EFFECTS ON EXAMINATION OUTCOMES

American Journal of Human Biology DOI 10.1002/ajhb

(newly entering) students are more difficult,and older students have a greater chance ofdoing well (multiple regression analysis: r2 ¼0.526, F ¼ 41.02, P < 0.001; year of birth: b ¼�0.336, P < 0.001; year of study: b ¼ 0.643, P< 0.001); and 2) students not doing well oftenleave university before attaining a degree.Figure 1 (inset b) shows that the sinusoidal

fluctuation with a 1-year period has its maxi-mum (the highest marks awarded) for May-born female students, and its minimum (thelowest marks awarded) for November-bornfemale students. Accordingly, we found a sig-nificant positive correlation between photo-period and average examination score for eachbirth week of female (but not male) studentsborn in 1967–1977 (females: r2 ¼ 0.195, df ¼51, P ¼ 0.001; males: r2 ¼ 0.030, df ¼ 51, P ¼

0.216). The lack of significance in males mightbe also attributed to higher variance in themale sample.

The distribution of age at examination didnot match the age effect found in primaryschool children. Autumn- and winter-born stu-dents are older at time of examinations thanare spring- and summer-born students, andsummer-born students are the youngest (H-test: females, w2 ¼ 56.42, P < 0.001; males, w2 ¼26.0, P < 0.001), yet receive higher scores thanwinter- and autumn-born students (Table 1).

DISCUSSION

We find that examination scores are relatedto season of birth in both female and male stu-dents, indicating that there could be some bio-

Fig. 1. Periodicity of examination results with respect to week of birth. Week of birth averages of scores for femalestudents born in 1967–1976, linear regression, and main Fourier component with a 52-week period. Inset a: Lomb-Scargle periodogram of weekly averages. Red ‘‘spike’’ shows significant periodicity (P < 0.001, with 52-week period).Inset b: Periodic function over one year, for female sample. Labels on abscissa are not beginnings of months.

716 M. FIEDER ET AL.

American Journal of Human Biology DOI 10.1002/ajhb

logically significant underlying ontogenetic orearly life-history mechanism. Possible influen-ces could range from physiological mecha-nisms during pregnancy, to social and otherenvironmental influences after birth. Amongthe many environmental factors varying withseason, photoperiod might be involved in theunderlying mechanisms, as indicated by thecorrelation found between examination scoresand photoperiod at birth in female students.For instance, seasonal changes in photoperiodcould modulate brain development and neuro-transmitter systems. On the other hand, thediet of the mother during pregnancy may alsoaffect the development (particularly myelina-tion) of the fetal brain (Saugstadt, 1997).Both sexes show a different birth-season pat-

tern in examination results, indicating thatmales and females may react differently to sea-sonal influences during pregnancy and earlychildhood. It is frequently reported that sex-hormone levels vary with season (e.g., Kauppilaet al., 1987). In addition, there is evidence thatsex hormones play a role in neurodevelopmentlinked with cognitive function (Achiron et al.,2001). Thus, it could be speculated that season-ally varying sex-hormone levels in the motherand/or fetus might affect fetal brain develop-ment in a sex-specific manner.Our results indicate that cognitive ontogeny

in the developing organism might be suscepti-ble to seasonally varying influences duringlate pregnancy and/or early childhood with de-tectable consequences, manifest as a small-amplitude periodicity of examination perform-ance later in life.

ACKNOWLEDGMENTS

We thank G. Winckler (University of Vienna)for providing access to the data, and J. Rohlf(SUNY, Stony Brook, NY) for helpful discus-sions. S.H. was supported by the Austrian Pro-gram for Advanced Research and Technology of

the Austrian Academy of Sciences, and by theAustrian Science Fund (P18089-B03).

LITERATURE CITED

Achiron R, Lipitz S, Achiron A. 2001. Sex-related differen-ces in the development of human fetal corpus callosum:in utero ultrasonographic study. Prenat Diagn 21:116–120.

Bell JF, Massey A. 1994. Significance of birth-dates. Nature382:666.

Benderlioglu Z, Nelson RJ. 2004. Season of birth and fluctu-ating asymmetry. Am J Hum Biol 16:298–310.

Castrogiovanni P, Iapichino S, Pacchierotti C, Pieraccini F.1998. Season of birth in psychiatry: a review. Neuropsy-chobiology 37:175–181.

Chotai J, Forsgren T, Nilsson LG, Adolfsson R. 2001. Sea-son of birth variations in the temperament and characterinventory of personality in a general population. Neuro-psychobiology 44:19–26.

Huber S, Fieder M, Wallner B, Iber K, Moser G. 2004a. Sea-son of birth effects on reproduction in contemporaryhumans. Brief communication. Hum Reprod 19:445–447.

Huber S, Fieder M, Wallner B, Moser G, Arnold W. 2004b.Brief communication: birth month influences reproduc-tive performance in contemporary women. Hum Reprod19:1081–1082.

Hutchinson D, Sharp C. 1999. A lasting legacy? The per-sistence of season of birth effects. In: British educationalresearch association conference 1999-presented paper.Brighton, University of Sussex. p 1–10.

Kauppila A, Pakarinin A, Kirkinen P, Makila U. 1987. Theeffect of season on the circulating concentrations of ante-rior pituitary, ovarian and adrenal cortex hormones andhormone binding proteins in the subarctic area: evidenceon increased activity of the pituitary-ovarian axis inspring. Gynecol Endocrinol 1:137–150.

Livingston R, Adam BS, Bracha HS. 1993. Season of birthand neurodevelopmental disorders: summer birth isassociated with dyslexia. J Am Acad Child Psychiatry32:612–616.

Press WH, Teukolsky SA, Vetterling WT, Flannery BP.1992. Numerical recipes in C, 2nd ed. Cambridge: Cam-bridge University Press. 902 p.

Saugstadt LF. 1997. Optimal foetal growth in the reductionof learning and behaviour disorder and prevention ofsudden infant death (SIDS) after the first month. IntJ Psychophysiol 52:1–6.

Weber G, Prossinger H, Seidler H. 1998. Height depends onmonth of birth. Nature 391:754–755.

Williams P, Davies P, Evans R, Ferguson N. 1970. Season ofbirth and cognitive development. Nature 228:1033–1036.

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