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Historic Royal events and the male to female ratio at birth in the United Kingdom
European Journal of Obstetrics & Gynecology and Reproductive Biology 191 (2015) 57–61
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European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb
Historic Royal events and the male to female ratio at birth in the United Kingdom Victor Grech * Department of Paediatrics, Mater Dei Hospital, Malta
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 January 2015 Received in revised form 14 April 2015 Accepted 19 May 2015
Introduction: The male to female ratio of live births is expressed as the ratio of male live births divided by total live births (M/T). Factors which reduce M/T include toxins, stress and privation. Britain remains enamoured of the Monarchy. This study was carried out in order to ascertain whether Royal events influenced M/T in the UK. Materials and methods: Live births were analysed in relation to the birth of Prince Charles (1948), the Coronation of Queen Elizabeth II (1952), the Silver Jubilee (1977), the wedding of Diana Spencer to Charles, Prince of Wales (July 1981), the birth of Prince William (1982), the death of Lady Diana (August 1997), the wedding of Kate Middleton to Prince William (2011) and the Golden Jubilee (2002). Results: This study analysed 29,293,240 live births. There was a significant dip in M/T in the Coronation year (p = 0.03). M/T dipped significantly in relation to the Royal Wedding, commencing a year before (p < 0.0001). There were no significant M/T changes in relation to the Silver and Golden Jubilees. The birth of Prince William in 1982 resulted in a rise in M/T in the following year only (p = 0.016). Analysis by quarter in relation to Lady Diana’s death showed a decline in M/T 4–5 months later in the first quarter of 1998 (p = 0.046). Comments: The anticipation and stress leading to the Coronation and Royal Wedding may have depressed M/T. Increased coital rates associated with exuberance in relation to Prince William’s birth may have raised M/T. Lady Diana’s death was temporally associated with a decline in M/T. Royalty events may affect M/T ratios in Britain. ß 2015 Elsevier Ireland Ltd. All rights reserved.
Keywords: Great Britain Sex ratio Birth rate/*trends Infant Newborn
Introduction In mammals, gender is determined at conception and in humans, male live births occur slightly in excess. The male to female ratio of live births is expressed as the ratio of male live births divided by total live births and may be expressed as M/T [1]. Stress and M/T Many factors have been shown to influence M/T [1,2]. These include exposure to toxins (both occupational and population exposures) [2], natural calamities such as earthquakes [3] and floods [4], stress [5], and privation [6]. All of these factors tend to reduce M/T. Stress has been shown to be a particularly strong influence. For example, after the September 11 terrorist attacks on New York,
* Tel.: +356 99495813. E-mail address: [email protected] http://dx.doi.org/10.1016/j.ejogrb.2015.05.012 0301-2115/ß 2015 Elsevier Ireland Ltd. All rights reserved.
M/T fell sharply just three to four months later and recovered equally quickly [5]. Similarly, the 10-day war in Slovenia transiently but significantly depressed M/T [7]. However, conflicting results regarding the effects of stress have also been shown using similar datasets. For example, an analysis of the births in the Danish National Registers for 1980–1992 showed that exposure to severe life events tended to lower M/T [8]. In contrast, a study on the same but extended dataset (by one decade from 1993 to 2002) failed to replicate these findings [9]. Royalty and the public Despite British cynicism towards traditional institutions such as Parliament, the City, the press and the police, the populace remains wedded to the notion of a Monarchy. Indeed, surveys consistently show that less than a fifth of British subjects wish to abolish the Royal institution [10]. For these reasons, the actions of Royalty are avidly watched and for many, have a significant impact on everyday life, an interest that is further fuelled by the increasingly ubiquitous media [11].
V. Grech / European Journal of Obstetrics & Gynecology and Reproductive Biology 191 (2015) 57–61
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The British Isles have already been studied with regard to broad secular trends in M/T. There was an overall rise in M/T from the 1950s up to the late 1970s, followed by a decline thereafter. The step-down for the periods of 1975–1979 to 1980–1984 was highly significant (p = 0.001). An overall decreasing trend in M/T was noted (p = 0.04) [12]. It has also been shown that warfare did not significantly affect M/T, as, for example, in relation to the Falklands War [13]. This study was carried out in order to ascertain whether historic Royal occasions influenced M/T in the UK. Materials and methods Important dates related to the Monarchy for which M/T data was available included the birth of Prince Charles in 1948, Coronation of Queen Elizabeth II in 1952, the Silver Jubilee in 1977, the wedding of Diana Spencer to Charles, Prince of Wales in July 1981, the birth of Prince William in 1982, the death of Lady Diana in August 1997, the wedding of Kate Middleton to Prince William in 2011 and the Golden Jubilee in 2002. Annual male and female live births were obtained directly from a World Health Organisation Database (HFA (Health for All) Database) for all of the UK. Data was available for the period 1950– 2012. For the periods 1946–1950 and 2009–2013, data was available for England and Wales only from the Office for National Statistics, and this was used for the analysis pertaining to the birth
of Prince Charles and the wedding of Prince William and Kate Middleton. Comparisons of M/T for these five index years were made with the two preceding and following years. This was to minimise the influence of natural secular variation in M/T [14]. Monthly data (male and female live births) for England and Wales only was also available from 1997 to 2008 from the Life Events & Population Sources, Office for National Statistics, Hants, UK. This data was used to identify any potential fluctuations in M/T related to the death of Lady Diana in 31 August 1997 and the Golden Jubilee in 2002. Excel was used for data entry, overall analysis and charting. Sex odds were also calculated and tabulated (male divided by female births). The quadratic equations of Fleiss were used for exact calculation of 95% confidence intervals for ratios [15]. Chi tests and chi tests for trends for annual male and female births were used throughout using the Bio-Med-Stat Excel add-in for contingency tables [16]. A p-value 0.05 was taken to represent a statistically significant result.
Results This study analysed a total of 29,293,240 live births. Annual M/T for the index years and for the previous and following two years are shown in Table 1.
Table 1 M/T (and 95% confidence intervals) for the eight index years and two years prior and following each year. Birth of Prince Charlesa
M F T UCI M/T LCI RR
Wedding of Prince Charles to Diana Spencer
1946
1947
1948
1949
1950
422,299 398,420 820,719 0.5156 0.5145 0.5135 1.0599
453,590 427,436 881,026 0.5159 0.5148 0.5138 1.0612
399,112 376,194 775,306 0.5159 0.5148 0.5137 1.0609
376,064 354,454 730,518 0.5159 0.5148 0.5136 1.0610
358,715 338,382 697,097 0.5158 0.5146 0.5134 1.0601
1950
1951
1952
1953
1954
421,440 396,981 818,421 0.5160 0.5149 0.5139 1.0616
409,942 386,703 796,645 0.5157 0.5146 0.5135 1.0601
406,992 385,925 792,917 0.5144 0.5133 0.5122 1.0546
413,929 390,340 804,269 0.5158 0.5147 0.5136 1.0604
408,686 386,083 794,769 0.5153 0.5142 0.5131 1.0585
1975
1976
1977
1978
1979
359,243 338,275 697,518 0.5162 0.5150 0.5139 1.0620
347,356 328,170 675,526 0.5154 0.5142 0.5130 1.0585
337,559 317,880 655,439 0.5162 0.5150 0.5138 1.0619
354,688 333,930 688,618 0.5163 0.5151 0.5139 1.0622
378,836 355,708 734,544 0.5169 0.5157 0.5146 1.0650
M F T UCI M/T LCI RR
M F T UCI M/T LCI RR
Silver Jubilee
M F T UCI M/T LCI RR
1981
1982
1983
378,836 355,708 734,544 0.5169 0.5157 0.5146 1.0650
385,792 367,475 753,267 0.5133 0.5122 0.5110 1.0498
374,830 355,890 730,720 0.5141 0.5130 0.5118 1.0532
368,995 350,004 718,999 0.5144 0.5132 0.5121 1.0543
370,820 350,418 721,238 0.5153 0.5141 0.5130 1.0582
1995
1996
1997
1998
1999
375,133 356,749 731,882 0.5137 0.5126 0.5114 1.0515
376,395 356,768 733,163 0.5145 0.5134 0.5122 1.0550
371,913 353,707 725,620 0.5137 0.5125 0.5114 1.0515
367,457 349,431 716,888 0.5137 0.5126 0.5114 1.0516
359,444 340,532 699,976 0.5147 0.5135 0.5123 1.0555
2000
2001
2002
2003
2004
347,941 331,088 679,029 0.5136 0.5124 0.5112 1.0509
342,709 326,414 669,123 0.5134 0.5122 0.5110 1.0499
343,155 325,622 668,777 0.5143 0.5131 0.5119 1.0538
356,578 338,971 695,549 0.5138 0.5127 0.5115 1.0519
367,586 348,410 715,996 0.5145 0.5134 0.5122 1.0550
Golden Jubilee
M F T UCI M/T LCI RR
Wedding of Prince William and Kate Middletona
Birth of Prince William
M F T UCI M/T LCI RR
1980
Death of Lady Diana
Coronation
M F T UCI M/T LCI RR
1979
1980
1981
1982
1983
1984
385,792 367,475 753,267 0.5133 0.5122 0.5110 1.0498
374,830 355,890 730,720 0.5141 0.5130 0.5118 1.0532
368,995 350,004 718,999 0.5144 0.5132 0.5121 1.0543
370,820 350,418 721,238 0.5153 0.5141 0.5130 1.0582
373,379 356,022 729,401 0.5130 0.5119 0.5108 1.0488
UCI and LCI: upper and lower confidence intervals. a England and Wales only
M F T UCI M/T LCI RR
2009
2010
2011
2012
2013
362,135 344,113 706,248 0.5139 0.5128 0.5116 1.0524
370,966 352,199 723,165 0.5141 0.5130 0.5118 1.0533
370,974 352,939 723,913 0.5136 0.5125 0.5113 1.0511
374,346 355,328 729,674 0.5142 0.5130 0.5119 1.0535
358,383 340,129 698,512 0.5142 0.5131 0.5119 1.0537
V. Grech / European Journal of Obstetrics & Gynecology and Reproductive Biology 191 (2015) 57–61
59
Fig. 1. M/T (along with 95% confidence intervals) for the index years and two years preceding and following each year.
Fig. 2. Quarterly M/T for England and Wales (along with 95% confidence intervals) for 1997 and 1998.
There was a significant dip in M/T in 1952, the Coronation year, compared to the preceding and following two years (chi = 4.4, p = 0.03, Fig. 1). M/T dipped significantly in relation to the Royal wedding, commencing a year before (2 2 for 1979 vs. 1980, chi = 19.1, p < 0.0001). M/T normalised over the next few years and this rise (1980–83) was significant (Chi for linear trend = 5.7, p = 0.017, Fig. 1). The birth of Prince William in 1982 resulted in a sharp and significant rise in M/T in the following year only when compared to the other four years (chi = 5.9, p = 0.016).
There were no significant fluctuations in annual M/T in relation the birth of Prince Charles in 1948, to the Silver Jubilee in 1977, the Golden Jubilee in 2002 and to death of Lady Diana (Fig. 1). The wedding of Prince William and Kate Middleton in 2011 resulted in a small but non-significant dip in M/T in that same year. Monthly analysis for the data available in relation to Lady Diana’s death in August 1997 showed a decline in M/T in the first three months of 1998 (Fig. 2). Analysis by quarter showed that M/T in the first quarter of 1998 was significantly lower than that of the last quarter of 1997 and the second quarter of 1998 (p = 0.046, Table 2). This finding could not be replicated by extending the same analysis to the following three years and to their sum. Monthly and quarterly analysis for M/T in relation to the Golden Jubilee in 2002 failed to detect any significant changes in M/T in the nine months following the celebrations which occurred between May and July 2002, peaking in early June. Comments M/T and stress M/T declines in response to adverse environmental factors such as stressful events, and this is in accordance with the Trivers–Willard
Table 2 M/T and analysis testing for the 1st quarters of 1998–2000. Chi tests for index quarters vs. previous and following quarters and chi tests for index quarters vs. sum of previous and following quarters.
M F Total UCI M/T LCI Chi p
M F Total UCI M/T LCI Chi p
1997 Q4
1998 Q1
1998 Q2
1998 Q4
1999 Q1
1999 Q2
1999 Q4
2000 Q1
2000 Q2
2000 Q4
2001 Q1
2001 Q2
80,382 76,255 156,637 0.5157 0.5132 0.5107
79,601 76,243 155,844 0.5133 0.5108 0.5083 1.8 ns
81,583 76,975 158,558 0.5170 0.5145 0.5121 4.4 0.035
79,654 75,705 155,359 0.5152 0.5127 0.5102
78,143 73,938 152,081 0.5163 0.5138 0.5113 0.4 ns
80,819 76,431 157,250 0.5164 0.5140 0.5115 0.0 ns
78,047 74,373 152,420 0.5146 0.5121 0.5095
75,973 72,706 148,679 0.5135 0.5110 0.5084 0.3 ns
77,488 73,212 150,700 0.5167 0.5142 0.5117 3.1 ns
76,792 73,296 150,088 0.5142 0.5116 0.5091
74,279 71,255 145,534 0.5130 0.5104 0.5078 0.5 ns
76,157 72,605 148,762 0.5145 0.5119 0.5094 0.7 ns
1998 Q1
Q4+Q2
1999 Q1
Q4+Q2
2000 Q1
Q4+Q2
2001 Q1
Q4+Q2
Q1 ‘99–01
Q4+Q2
79,601 76,243 155,844 0.5133 0.5108 0.5083
161,965 153,230 315,195 0.5156 0.5139 0.5121 4.0 0.046
78,143 73,938 152,081 0.5163 0.5138 0.5113
160,473 152,136 312,609 0.5151 0.5133 0.5116 0.1 ns
75,973 72,706 148,679 0.5135 0.5110 0.5084
155,535 147,585 303,120 0.5149 0.5131 0.5113 1.8 ns
74,279 71,255 145,534 0.5130 0.5104 0.5078
152,949 145,901 298,850 0.5136 0.5118 0.5100 0.8 ns
228,395 217,899 446,294 0.5132 0.5118 0.5103
468,957 445,622 914,579 0.5138 0.5128 0.5117 1.2 ns
UCI and LCI: upper and lower confidence intervals.
60
V. Grech / European Journal of Obstetrics & Gynecology and Reproductive Biology 191 (2015) 57–61
hypothesis which proposes that natural selection has favoured parents who bias investment in favour of the sex with the best reproductive prospects in accordance with extant periconceptual and gestational conditions [17]. For example, poor conditions may preclude the carriage of a male baby to term since a male requires greater maternal resources for gestation [18]. Furthermore, should such pregnancies manage to arrive to term, the outcome may be a frail male who may not survive infancy and childhood. Moreover, a frail adult male would not be able to compete for mating privileges with stronger males. However, even under adverse circumstances, a female fetus is likelier to be successfully carried to term and survive, and eventually have offspring of her own. On the other hand, under favourable conditions, a robust male has far more reproductive opportunities than an equivalent female who is hampered by a long gestational period and subsequent nursing. Thus, since resource abundance or scarcity affects reproductive success, the Trivers–Willard hypothesis predicts that natural selection has favoured parents who tend to produce females under poor conditions and males in good circumstances [17]. It has been suggested that one possible mechanism is via a process of excess prenatal fetal losses which are skewed such that males are lost at a higher rate than females. Stress is an unfavourable condition and it has been shown that it induces spontaneous termination of pregnancy which affects male pregnancies in excess of female pregnancies [19]. The Monarchy This institution continues to be revered by the nation [10]. Indeed, for example, despite post-World War II austerity, it was decided that the Coronation of Queen Elizabeth II would be an extravagant affair replete with all possible pomp and pageantry [20]. Political and related events have been shown to influence M/T. For example, United States legislation enacted to facilitate the resettlement of Cuban refugees in the US was shown to have repeatedly influenced M/T [21]. And in Malta, parliamentary elections and important referenda have also been shown to influence M/T [22]. It is therefore not surprising that some of the events studied in this paper affected M/T. It is interesting to note that only the Coronation and the Royal Wedding influenced M/T. A possible explanation is that for both events, there was a significant build-up in preparations and hence in anticipation [20,23,24]. This was particularly so in the case of the Royal Wedding which at the time, seemed like a fairy-tale match [24]. Dips in M/T have been noted as if in anticipation of events that are momentous to population groupings. For example, in Mexico, M/T fell in 1970 (p < 0.0001), a year in which Mexico hosted the World Cup. M/T also fell in Mexico in 1987 (p < 0.0001), the year after the event was again also hosted in this country [25]. Football is a passion for many Latino countries [26], and it has been postulated that stress and anticipation leading up to the events may have somehow influenced M/T, leading to the observed declines in 1970 and 1987 in Mexico [25]. It is possible that similar mechanisms may have influenced M/T in the UK in relation to the anticipated Coronation and the Royal Wedding. The Silver and Golden Jubilees may not have caused as much furore and anticipation, and hence, were less likely to perturb M/T [27]. Sudden stressful events have been noted to swiftly but only transiently lower M/T [6]. This may only be evident on inspection of microdata such as annual or quarterly analysis, as was evidenced in Ireland after the economic crash in the last quarter of 2007 only, and in New York three months after September 11 [28].
The death of the Princess of Wales in 1997 certainly qualified as a significantly stressful event for a substantial proportion of the populace since she was perceived as being accessible and tangible, with high popularity ratings [29]. Her death was followed by a media reaction that was unprecedented in intensity and scale [30]. There appeared to be an explosion of feelings that crossed all boundaries of class, race, gender, age and political and intellectual leanings [31]. Interestingly, the September 11 attacks depressed M/T and this was shown to have occurred not only in New York [5], but also in California in the absence of an active threat [32]. It was also demonstrated that the attacks affected the entire United States, with an transient reduction in M/T due to excess male fetal losses [19]. Lady Diana’s death led to widespread mass mourning with an unprecedented outpouring of public grief. The engendered angst sufficed to significantly increase suicide rates and episodes of significant self-harm in England and Wales which rose by 17% and 44.3% respectively during the four weeks following the funeral [20]. It was suggested that in many cases, the mechanism of this effect was through the amplification of personal losses or the exacerbation of existing distress [11,20]. It was also suggested that an ‘‘identification’’ effect was present since the greatest increase in suicides was by women aged 25–44, wherein suicide rates increased by over 45% [33]. It is possible that these reactions led to the transient reduction in M/T that this study has detected in the first quarter of 1998, five months after Diana’s death in August 1997. The birth of Prince William in 1982 resulted in a sharp and significant rise in M/T in the following year only. M/T follows a Ushaped regression on cycle day of insemination, suggesting that female conceptions result most often from conceptions around ovulation, with male conceptions occurring more frequently at the beginning and end of the menstrual cycle [34,35]. These findings have been confirmed by more recent meta-analysis [36]. The rise in M/T in 1983 may thus have been due to higher coital rates associated with the exuberance linked to this particular event, transiently skewing M/T towards more male births. This is reinforced by a recent study that showed that male births rose in Hong Kong in relation to Dragon years since such years are considered auspicious for baby’s births, in accordance with the Chinese Zodiac. The putative mechanism may be similar, with increased coital activity since parents actively seek to conceive a child in Dragon years [37]. However, it has been noted that the sex ratio at birth continues to attract scientific attention because it is so easy to measure. Thus, from the multitude of studies, when striking findings emerge, researchers may be tempted to attribute plausible but not necessarily accurate biological mechanisms [38]. It was also impossible for this study to eliminate the effects of potential confounders due to data limitations. This is the first study to show a possible effect on M/T due to the events related to British Royalty, namely reductions in annual M/T in association with the coronation of Queen Elizabeth II and the marriage of Diana Spencer to Prince Charles, and a more transient reduction in M/T in response to Diana’s death. This study has also shown a rise in M/T temporally associated with a Royal birth, that of Prince William in 1982. M/T may thus be a sensitive and relatively impartial retrospective indicator of population stress. Competing interests None. Funding None.
V. Grech / European Journal of Obstetrics & Gynecology and Reproductive Biology 191 (2015) 57–61
Acknowledgments These individuals helped the author to access the relevant datasets: Mie Inoue and Gauden Galea from the World Health Organisation. Debbie Hague, Life Events & Population Sources, Office for National Statistics, Hants, UK. Dr. Julian Eason, Corniche Hospital, UAE, for study concept. References [1] James WH. The human sex ratio. Part 1: A review of the literature. Hum Biol 1987;59:721–52. [2] James WH. The human sex ratio. Part 2: A hypothesis and a program of research. Hum Biol 1987;59:873–900. [3] Fukuda M, Fukuda K, Shimizu T, Møller H. Decline in sex ratio at birth after Kobe earthquake. Hum Reprod 1998;13:2321–2. [4] Lyster WR. Altered sex ratio after the London smog of 1952 and the Brisbane flood of 1965. J Obstet Gynaecol Br Commonw 1974;81:626–31. [5] Catalano R, Bruckner T, Marks AR, Eskenazi B. Exogenous shocks to the human sex ratio: the case of September 11, 2001 in New York City. Hum Reprod 2006;21:3127–31. [6] Song S. Does famine influence sex ratio at birth? Evidence from the 1959–1961 Great Leap Forward Famine in China. Proc R Soc B: Biol Sci 2012;279:2883–90. [7] Zorn B, Sucur V, Stare J, Meden-Vrtovec H. Decline in sex ratio at birth after 10day war in Slovenia: brief communication. Hum Reprod 2002;17:3173–7. [8] Hansen D, Moller H, Olsen J. Severe periconceptional life events and the sex ratio in offspring: follow up study based on five national registers. Br Med J 1999;319:548–9. [9] Khashan AS, Mortensen PB, McNamee R, Baker PN, Abel KM. Sex ratio at birth following prenatal maternal exposure to severe life events: a populationbased cohort study. Hum Reprod 2009;24:1754–7. [10] Ipsos Mori, King’s College London. Royal Family & The Monarchy; November 2012. [11] Thomas J. From people power to mass hysteria media and popular reactions to the death of Princess Diana. Int J Cult Stud 2008;11:362–76. [12] Grech V. Sex ratios at birth in the British Isles over the past sixty years. Eur J Pediatr 2013;172:525–8. [13] Grech V. Conflicts in the last fifty years and subsequent effects on the male:female ratio at birth. Br J Med Med Res 2015;5:1247–54. [14] Gini C. Sulla probabilita che termini di una serie erratica sieno tutti crescenti (o non decrescenti) ovvero tutti decrescenti (o non crescenti) con applicazioni ai rapporti dei sessi nascite umane in intervalli successivi e alle disposizioni dei sessi nelle fratellanze umane. Metron 1955;17:1–41. [15] Fleiss JL. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley and Sons; 1981. p. 14–5.
61
[16] Sleza´k P. Microsoft Excel add-in for the statistical analysis of contingency tables. Int J Innovat Educ Res 2014;2:90–100. [17] Trivers RL, Willard DE. Natural selection of parental ability to vary the sex ratio of offspring. Science 1973;179:90–2. [18] Myers JH. Sex ratio adjustment under food stress: maximization of quality or numbers of offspring? Am Nat 1978;112:381–8. [19] Bruckner TA, Catalano R, Ahern J. Male fetal loss in the U.S. following the terrorist attacks of September 11, 2001. BMC Public Health 2010;10:273. [20] Shils E, Young M. The meaning of the Coronation. Sociol Rev 1953;1: 63–81. [21] Grech V. The influence of migration on secular trends in sex ratios at birth in Cuba in the past fifty years. West Indian Med J 2014;63:6–10. [22] Grech V. The male:female ratio at birth is depressed by Maltese parliamentary elections and increased by other non-electoral events. Int J Trop Dis Health 2014;4:1123–31. [23] Davidson D. An adolescent in search of her identity. J Anal Psychol 1985;30:339–46. [24] Denney C. Representing Diana, Princess of Wales: cultural memory and fairy tales revisited. Madison: Fairleigh Dickinson Univ Press; 2005. [25] Grech V. Soccer World Cup influences sex ratio at birth. Eur J Sports Med 2014;2:21–9. [26] Mason T. Passion of the people? Football in South America: Football. New York: Verso Books; 1995. [27] Bousfield A, Toffoli G. Fifty years the queen: a tribute to her Majesty Queen Elizabeth II on her golden jubilee. Toronto: Dundurn; 2002. [28] Grech V. Economic stress and the secondary sex ratio: Ireland, Iceland, Greece and Latvia. Int J Trop Dis Health 2015;5:252–9. [29] Watson CW. ‘‘Born a Lady, Became a Princess, Died a Saint’’: The Reaction to the Death of Diana, Princess of Wales. Anthropol Today 1997;13:3–7. [30] Turner G, Bonner F, Marshall D. Fame games: the production of celebrity. Cambridge: Cambridge University Press; 2000. [31] Gilbert J, Glover D, Kaplan C, Bourne Taylor J, Wheeler W. Diana and Democracy, Special Issue, New Formations 36; 1999. [32] Catalano R, Bruckner T, Gould J, Eskenazi B, Anderson E. Sex ratios in California following the terrorist attacks of September 11, 2001. Hum Reprod 2005;20:1221–7. [33] Hawton K, Harriss L, Simkin S, et al. Effect of death of Diana, Princess of Wales on suicide and deliberate self-harm. Br J Psychiatry 2000;177:463–6. [34] Guerrero R. Association of the type and time of insemination within the menstrual cycle with the human sex ratio at birth. N Engl J Med 1974;291:1056–9. [35] Harlap S. Gender of infants conceived on different days of the menstrual cycle. N Engl J Med 1979;300:1445–8. [36] Gray RH. Natural family planning and sex selection: fact or fiction? Am J Obstet Gynecol 1991;165:1982–4. [37] Grech V. The influence of the Chinese zodiac on the male-to-female ratio at birth in Hong Kong. J Chin Med Assoc 2015;78(5):287–91. [38] Bonde JP, Wilcox A. Ratio of boys to girls at birth. Br Med J 2007;334:486–7.
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European Journal of Obstetrics & Gynecology and Reproductive Biology journal homepage: www.elsevier.com/locate/ejogrb
Historic Royal events and the male to female ratio at birth in the United Kingdom Victor Grech * Department of Paediatrics, Mater Dei Hospital, Malta
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 January 2015 Received in revised form 14 April 2015 Accepted 19 May 2015
Introduction: The male to female ratio of live births is expressed as the ratio of male live births divided by total live births (M/T). Factors which reduce M/T include toxins, stress and privation. Britain remains enamoured of the Monarchy. This study was carried out in order to ascertain whether Royal events influenced M/T in the UK. Materials and methods: Live births were analysed in relation to the birth of Prince Charles (1948), the Coronation of Queen Elizabeth II (1952), the Silver Jubilee (1977), the wedding of Diana Spencer to Charles, Prince of Wales (July 1981), the birth of Prince William (1982), the death of Lady Diana (August 1997), the wedding of Kate Middleton to Prince William (2011) and the Golden Jubilee (2002). Results: This study analysed 29,293,240 live births. There was a significant dip in M/T in the Coronation year (p = 0.03). M/T dipped significantly in relation to the Royal Wedding, commencing a year before (p < 0.0001). There were no significant M/T changes in relation to the Silver and Golden Jubilees. The birth of Prince William in 1982 resulted in a rise in M/T in the following year only (p = 0.016). Analysis by quarter in relation to Lady Diana’s death showed a decline in M/T 4–5 months later in the first quarter of 1998 (p = 0.046). Comments: The anticipation and stress leading to the Coronation and Royal Wedding may have depressed M/T. Increased coital rates associated with exuberance in relation to Prince William’s birth may have raised M/T. Lady Diana’s death was temporally associated with a decline in M/T. Royalty events may affect M/T ratios in Britain. ß 2015 Elsevier Ireland Ltd. All rights reserved.
Keywords: Great Britain Sex ratio Birth rate/*trends Infant Newborn
Introduction In mammals, gender is determined at conception and in humans, male live births occur slightly in excess. The male to female ratio of live births is expressed as the ratio of male live births divided by total live births and may be expressed as M/T [1]. Stress and M/T Many factors have been shown to influence M/T [1,2]. These include exposure to toxins (both occupational and population exposures) [2], natural calamities such as earthquakes [3] and floods [4], stress [5], and privation [6]. All of these factors tend to reduce M/T. Stress has been shown to be a particularly strong influence. For example, after the September 11 terrorist attacks on New York,
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M/T fell sharply just three to four months later and recovered equally quickly [5]. Similarly, the 10-day war in Slovenia transiently but significantly depressed M/T [7]. However, conflicting results regarding the effects of stress have also been shown using similar datasets. For example, an analysis of the births in the Danish National Registers for 1980–1992 showed that exposure to severe life events tended to lower M/T [8]. In contrast, a study on the same but extended dataset (by one decade from 1993 to 2002) failed to replicate these findings [9]. Royalty and the public Despite British cynicism towards traditional institutions such as Parliament, the City, the press and the police, the populace remains wedded to the notion of a Monarchy. Indeed, surveys consistently show that less than a fifth of British subjects wish to abolish the Royal institution [10]. For these reasons, the actions of Royalty are avidly watched and for many, have a significant impact on everyday life, an interest that is further fuelled by the increasingly ubiquitous media [11].
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The British Isles have already been studied with regard to broad secular trends in M/T. There was an overall rise in M/T from the 1950s up to the late 1970s, followed by a decline thereafter. The step-down for the periods of 1975–1979 to 1980–1984 was highly significant (p = 0.001). An overall decreasing trend in M/T was noted (p = 0.04) [12]. It has also been shown that warfare did not significantly affect M/T, as, for example, in relation to the Falklands War [13]. This study was carried out in order to ascertain whether historic Royal occasions influenced M/T in the UK. Materials and methods Important dates related to the Monarchy for which M/T data was available included the birth of Prince Charles in 1948, Coronation of Queen Elizabeth II in 1952, the Silver Jubilee in 1977, the wedding of Diana Spencer to Charles, Prince of Wales in July 1981, the birth of Prince William in 1982, the death of Lady Diana in August 1997, the wedding of Kate Middleton to Prince William in 2011 and the Golden Jubilee in 2002. Annual male and female live births were obtained directly from a World Health Organisation Database (HFA (Health for All) Database) for all of the UK. Data was available for the period 1950– 2012. For the periods 1946–1950 and 2009–2013, data was available for England and Wales only from the Office for National Statistics, and this was used for the analysis pertaining to the birth
of Prince Charles and the wedding of Prince William and Kate Middleton. Comparisons of M/T for these five index years were made with the two preceding and following years. This was to minimise the influence of natural secular variation in M/T [14]. Monthly data (male and female live births) for England and Wales only was also available from 1997 to 2008 from the Life Events & Population Sources, Office for National Statistics, Hants, UK. This data was used to identify any potential fluctuations in M/T related to the death of Lady Diana in 31 August 1997 and the Golden Jubilee in 2002. Excel was used for data entry, overall analysis and charting. Sex odds were also calculated and tabulated (male divided by female births). The quadratic equations of Fleiss were used for exact calculation of 95% confidence intervals for ratios [15]. Chi tests and chi tests for trends for annual male and female births were used throughout using the Bio-Med-Stat Excel add-in for contingency tables [16]. A p-value 0.05 was taken to represent a statistically significant result.
Results This study analysed a total of 29,293,240 live births. Annual M/T for the index years and for the previous and following two years are shown in Table 1.
Table 1 M/T (and 95% confidence intervals) for the eight index years and two years prior and following each year. Birth of Prince Charlesa
M F T UCI M/T LCI RR
Wedding of Prince Charles to Diana Spencer
1946
1947
1948
1949
1950
422,299 398,420 820,719 0.5156 0.5145 0.5135 1.0599
453,590 427,436 881,026 0.5159 0.5148 0.5138 1.0612
399,112 376,194 775,306 0.5159 0.5148 0.5137 1.0609
376,064 354,454 730,518 0.5159 0.5148 0.5136 1.0610
358,715 338,382 697,097 0.5158 0.5146 0.5134 1.0601
1950
1951
1952
1953
1954
421,440 396,981 818,421 0.5160 0.5149 0.5139 1.0616
409,942 386,703 796,645 0.5157 0.5146 0.5135 1.0601
406,992 385,925 792,917 0.5144 0.5133 0.5122 1.0546
413,929 390,340 804,269 0.5158 0.5147 0.5136 1.0604
408,686 386,083 794,769 0.5153 0.5142 0.5131 1.0585
1975
1976
1977
1978
1979
359,243 338,275 697,518 0.5162 0.5150 0.5139 1.0620
347,356 328,170 675,526 0.5154 0.5142 0.5130 1.0585
337,559 317,880 655,439 0.5162 0.5150 0.5138 1.0619
354,688 333,930 688,618 0.5163 0.5151 0.5139 1.0622
378,836 355,708 734,544 0.5169 0.5157 0.5146 1.0650
M F T UCI M/T LCI RR
M F T UCI M/T LCI RR
Silver Jubilee
M F T UCI M/T LCI RR
1981
1982
1983
378,836 355,708 734,544 0.5169 0.5157 0.5146 1.0650
385,792 367,475 753,267 0.5133 0.5122 0.5110 1.0498
374,830 355,890 730,720 0.5141 0.5130 0.5118 1.0532
368,995 350,004 718,999 0.5144 0.5132 0.5121 1.0543
370,820 350,418 721,238 0.5153 0.5141 0.5130 1.0582
1995
1996
1997
1998
1999
375,133 356,749 731,882 0.5137 0.5126 0.5114 1.0515
376,395 356,768 733,163 0.5145 0.5134 0.5122 1.0550
371,913 353,707 725,620 0.5137 0.5125 0.5114 1.0515
367,457 349,431 716,888 0.5137 0.5126 0.5114 1.0516
359,444 340,532 699,976 0.5147 0.5135 0.5123 1.0555
2000
2001
2002
2003
2004
347,941 331,088 679,029 0.5136 0.5124 0.5112 1.0509
342,709 326,414 669,123 0.5134 0.5122 0.5110 1.0499
343,155 325,622 668,777 0.5143 0.5131 0.5119 1.0538
356,578 338,971 695,549 0.5138 0.5127 0.5115 1.0519
367,586 348,410 715,996 0.5145 0.5134 0.5122 1.0550
Golden Jubilee
M F T UCI M/T LCI RR
Wedding of Prince William and Kate Middletona
Birth of Prince William
M F T UCI M/T LCI RR
1980
Death of Lady Diana
Coronation
M F T UCI M/T LCI RR
1979
1980
1981
1982
1983
1984
385,792 367,475 753,267 0.5133 0.5122 0.5110 1.0498
374,830 355,890 730,720 0.5141 0.5130 0.5118 1.0532
368,995 350,004 718,999 0.5144 0.5132 0.5121 1.0543
370,820 350,418 721,238 0.5153 0.5141 0.5130 1.0582
373,379 356,022 729,401 0.5130 0.5119 0.5108 1.0488
UCI and LCI: upper and lower confidence intervals. a England and Wales only
M F T UCI M/T LCI RR
2009
2010
2011
2012
2013
362,135 344,113 706,248 0.5139 0.5128 0.5116 1.0524
370,966 352,199 723,165 0.5141 0.5130 0.5118 1.0533
370,974 352,939 723,913 0.5136 0.5125 0.5113 1.0511
374,346 355,328 729,674 0.5142 0.5130 0.5119 1.0535
358,383 340,129 698,512 0.5142 0.5131 0.5119 1.0537
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Fig. 1. M/T (along with 95% confidence intervals) for the index years and two years preceding and following each year.
Fig. 2. Quarterly M/T for England and Wales (along with 95% confidence intervals) for 1997 and 1998.
There was a significant dip in M/T in 1952, the Coronation year, compared to the preceding and following two years (chi = 4.4, p = 0.03, Fig. 1). M/T dipped significantly in relation to the Royal wedding, commencing a year before (2 2 for 1979 vs. 1980, chi = 19.1, p < 0.0001). M/T normalised over the next few years and this rise (1980–83) was significant (Chi for linear trend = 5.7, p = 0.017, Fig. 1). The birth of Prince William in 1982 resulted in a sharp and significant rise in M/T in the following year only when compared to the other four years (chi = 5.9, p = 0.016).
There were no significant fluctuations in annual M/T in relation the birth of Prince Charles in 1948, to the Silver Jubilee in 1977, the Golden Jubilee in 2002 and to death of Lady Diana (Fig. 1). The wedding of Prince William and Kate Middleton in 2011 resulted in a small but non-significant dip in M/T in that same year. Monthly analysis for the data available in relation to Lady Diana’s death in August 1997 showed a decline in M/T in the first three months of 1998 (Fig. 2). Analysis by quarter showed that M/T in the first quarter of 1998 was significantly lower than that of the last quarter of 1997 and the second quarter of 1998 (p = 0.046, Table 2). This finding could not be replicated by extending the same analysis to the following three years and to their sum. Monthly and quarterly analysis for M/T in relation to the Golden Jubilee in 2002 failed to detect any significant changes in M/T in the nine months following the celebrations which occurred between May and July 2002, peaking in early June. Comments M/T and stress M/T declines in response to adverse environmental factors such as stressful events, and this is in accordance with the Trivers–Willard
Table 2 M/T and analysis testing for the 1st quarters of 1998–2000. Chi tests for index quarters vs. previous and following quarters and chi tests for index quarters vs. sum of previous and following quarters.
M F Total UCI M/T LCI Chi p
M F Total UCI M/T LCI Chi p
1997 Q4
1998 Q1
1998 Q2
1998 Q4
1999 Q1
1999 Q2
1999 Q4
2000 Q1
2000 Q2
2000 Q4
2001 Q1
2001 Q2
80,382 76,255 156,637 0.5157 0.5132 0.5107
79,601 76,243 155,844 0.5133 0.5108 0.5083 1.8 ns
81,583 76,975 158,558 0.5170 0.5145 0.5121 4.4 0.035
79,654 75,705 155,359 0.5152 0.5127 0.5102
78,143 73,938 152,081 0.5163 0.5138 0.5113 0.4 ns
80,819 76,431 157,250 0.5164 0.5140 0.5115 0.0 ns
78,047 74,373 152,420 0.5146 0.5121 0.5095
75,973 72,706 148,679 0.5135 0.5110 0.5084 0.3 ns
77,488 73,212 150,700 0.5167 0.5142 0.5117 3.1 ns
76,792 73,296 150,088 0.5142 0.5116 0.5091
74,279 71,255 145,534 0.5130 0.5104 0.5078 0.5 ns
76,157 72,605 148,762 0.5145 0.5119 0.5094 0.7 ns
1998 Q1
Q4+Q2
1999 Q1
Q4+Q2
2000 Q1
Q4+Q2
2001 Q1
Q4+Q2
Q1 ‘99–01
Q4+Q2
79,601 76,243 155,844 0.5133 0.5108 0.5083
161,965 153,230 315,195 0.5156 0.5139 0.5121 4.0 0.046
78,143 73,938 152,081 0.5163 0.5138 0.5113
160,473 152,136 312,609 0.5151 0.5133 0.5116 0.1 ns
75,973 72,706 148,679 0.5135 0.5110 0.5084
155,535 147,585 303,120 0.5149 0.5131 0.5113 1.8 ns
74,279 71,255 145,534 0.5130 0.5104 0.5078
152,949 145,901 298,850 0.5136 0.5118 0.5100 0.8 ns
228,395 217,899 446,294 0.5132 0.5118 0.5103
468,957 445,622 914,579 0.5138 0.5128 0.5117 1.2 ns
UCI and LCI: upper and lower confidence intervals.
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hypothesis which proposes that natural selection has favoured parents who bias investment in favour of the sex with the best reproductive prospects in accordance with extant periconceptual and gestational conditions [17]. For example, poor conditions may preclude the carriage of a male baby to term since a male requires greater maternal resources for gestation [18]. Furthermore, should such pregnancies manage to arrive to term, the outcome may be a frail male who may not survive infancy and childhood. Moreover, a frail adult male would not be able to compete for mating privileges with stronger males. However, even under adverse circumstances, a female fetus is likelier to be successfully carried to term and survive, and eventually have offspring of her own. On the other hand, under favourable conditions, a robust male has far more reproductive opportunities than an equivalent female who is hampered by a long gestational period and subsequent nursing. Thus, since resource abundance or scarcity affects reproductive success, the Trivers–Willard hypothesis predicts that natural selection has favoured parents who tend to produce females under poor conditions and males in good circumstances [17]. It has been suggested that one possible mechanism is via a process of excess prenatal fetal losses which are skewed such that males are lost at a higher rate than females. Stress is an unfavourable condition and it has been shown that it induces spontaneous termination of pregnancy which affects male pregnancies in excess of female pregnancies [19]. The Monarchy This institution continues to be revered by the nation [10]. Indeed, for example, despite post-World War II austerity, it was decided that the Coronation of Queen Elizabeth II would be an extravagant affair replete with all possible pomp and pageantry [20]. Political and related events have been shown to influence M/T. For example, United States legislation enacted to facilitate the resettlement of Cuban refugees in the US was shown to have repeatedly influenced M/T [21]. And in Malta, parliamentary elections and important referenda have also been shown to influence M/T [22]. It is therefore not surprising that some of the events studied in this paper affected M/T. It is interesting to note that only the Coronation and the Royal Wedding influenced M/T. A possible explanation is that for both events, there was a significant build-up in preparations and hence in anticipation [20,23,24]. This was particularly so in the case of the Royal Wedding which at the time, seemed like a fairy-tale match [24]. Dips in M/T have been noted as if in anticipation of events that are momentous to population groupings. For example, in Mexico, M/T fell in 1970 (p < 0.0001), a year in which Mexico hosted the World Cup. M/T also fell in Mexico in 1987 (p < 0.0001), the year after the event was again also hosted in this country [25]. Football is a passion for many Latino countries [26], and it has been postulated that stress and anticipation leading up to the events may have somehow influenced M/T, leading to the observed declines in 1970 and 1987 in Mexico [25]. It is possible that similar mechanisms may have influenced M/T in the UK in relation to the anticipated Coronation and the Royal Wedding. The Silver and Golden Jubilees may not have caused as much furore and anticipation, and hence, were less likely to perturb M/T [27]. Sudden stressful events have been noted to swiftly but only transiently lower M/T [6]. This may only be evident on inspection of microdata such as annual or quarterly analysis, as was evidenced in Ireland after the economic crash in the last quarter of 2007 only, and in New York three months after September 11 [28].
The death of the Princess of Wales in 1997 certainly qualified as a significantly stressful event for a substantial proportion of the populace since she was perceived as being accessible and tangible, with high popularity ratings [29]. Her death was followed by a media reaction that was unprecedented in intensity and scale [30]. There appeared to be an explosion of feelings that crossed all boundaries of class, race, gender, age and political and intellectual leanings [31]. Interestingly, the September 11 attacks depressed M/T and this was shown to have occurred not only in New York [5], but also in California in the absence of an active threat [32]. It was also demonstrated that the attacks affected the entire United States, with an transient reduction in M/T due to excess male fetal losses [19]. Lady Diana’s death led to widespread mass mourning with an unprecedented outpouring of public grief. The engendered angst sufficed to significantly increase suicide rates and episodes of significant self-harm in England and Wales which rose by 17% and 44.3% respectively during the four weeks following the funeral [20]. It was suggested that in many cases, the mechanism of this effect was through the amplification of personal losses or the exacerbation of existing distress [11,20]. It was also suggested that an ‘‘identification’’ effect was present since the greatest increase in suicides was by women aged 25–44, wherein suicide rates increased by over 45% [33]. It is possible that these reactions led to the transient reduction in M/T that this study has detected in the first quarter of 1998, five months after Diana’s death in August 1997. The birth of Prince William in 1982 resulted in a sharp and significant rise in M/T in the following year only. M/T follows a Ushaped regression on cycle day of insemination, suggesting that female conceptions result most often from conceptions around ovulation, with male conceptions occurring more frequently at the beginning and end of the menstrual cycle [34,35]. These findings have been confirmed by more recent meta-analysis [36]. The rise in M/T in 1983 may thus have been due to higher coital rates associated with the exuberance linked to this particular event, transiently skewing M/T towards more male births. This is reinforced by a recent study that showed that male births rose in Hong Kong in relation to Dragon years since such years are considered auspicious for baby’s births, in accordance with the Chinese Zodiac. The putative mechanism may be similar, with increased coital activity since parents actively seek to conceive a child in Dragon years [37]. However, it has been noted that the sex ratio at birth continues to attract scientific attention because it is so easy to measure. Thus, from the multitude of studies, when striking findings emerge, researchers may be tempted to attribute plausible but not necessarily accurate biological mechanisms [38]. It was also impossible for this study to eliminate the effects of potential confounders due to data limitations. This is the first study to show a possible effect on M/T due to the events related to British Royalty, namely reductions in annual M/T in association with the coronation of Queen Elizabeth II and the marriage of Diana Spencer to Prince Charles, and a more transient reduction in M/T in response to Diana’s death. This study has also shown a rise in M/T temporally associated with a Royal birth, that of Prince William in 1982. M/T may thus be a sensitive and relatively impartial retrospective indicator of population stress. Competing interests None. Funding None.
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Acknowledgments These individuals helped the author to access the relevant datasets: Mie Inoue and Gauden Galea from the World Health Organisation. Debbie Hague, Life Events & Population Sources, Office for National Statistics, Hants, UK. Dr. Julian Eason, Corniche Hospital, UAE, for study concept. References [1] James WH. The human sex ratio. Part 1: A review of the literature. Hum Biol 1987;59:721–52. [2] James WH. The human sex ratio. Part 2: A hypothesis and a program of research. Hum Biol 1987;59:873–900. [3] Fukuda M, Fukuda K, Shimizu T, Møller H. Decline in sex ratio at birth after Kobe earthquake. Hum Reprod 1998;13:2321–2. [4] Lyster WR. Altered sex ratio after the London smog of 1952 and the Brisbane flood of 1965. J Obstet Gynaecol Br Commonw 1974;81:626–31. [5] Catalano R, Bruckner T, Marks AR, Eskenazi B. Exogenous shocks to the human sex ratio: the case of September 11, 2001 in New York City. Hum Reprod 2006;21:3127–31. [6] Song S. Does famine influence sex ratio at birth? Evidence from the 1959–1961 Great Leap Forward Famine in China. Proc R Soc B: Biol Sci 2012;279:2883–90. [7] Zorn B, Sucur V, Stare J, Meden-Vrtovec H. Decline in sex ratio at birth after 10day war in Slovenia: brief communication. Hum Reprod 2002;17:3173–7. [8] Hansen D, Moller H, Olsen J. Severe periconceptional life events and the sex ratio in offspring: follow up study based on five national registers. Br Med J 1999;319:548–9. [9] Khashan AS, Mortensen PB, McNamee R, Baker PN, Abel KM. Sex ratio at birth following prenatal maternal exposure to severe life events: a populationbased cohort study. Hum Reprod 2009;24:1754–7. [10] Ipsos Mori, King’s College London. Royal Family & The Monarchy; November 2012. [11] Thomas J. From people power to mass hysteria media and popular reactions to the death of Princess Diana. Int J Cult Stud 2008;11:362–76. [12] Grech V. Sex ratios at birth in the British Isles over the past sixty years. Eur J Pediatr 2013;172:525–8. [13] Grech V. Conflicts in the last fifty years and subsequent effects on the male:female ratio at birth. Br J Med Med Res 2015;5:1247–54. [14] Gini C. Sulla probabilita che termini di una serie erratica sieno tutti crescenti (o non decrescenti) ovvero tutti decrescenti (o non crescenti) con applicazioni ai rapporti dei sessi nascite umane in intervalli successivi e alle disposizioni dei sessi nelle fratellanze umane. Metron 1955;17:1–41. [15] Fleiss JL. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley and Sons; 1981. p. 14–5.
61
[16] Sleza´k P. Microsoft Excel add-in for the statistical analysis of contingency tables. Int J Innovat Educ Res 2014;2:90–100. [17] Trivers RL, Willard DE. Natural selection of parental ability to vary the sex ratio of offspring. Science 1973;179:90–2. [18] Myers JH. Sex ratio adjustment under food stress: maximization of quality or numbers of offspring? Am Nat 1978;112:381–8. [19] Bruckner TA, Catalano R, Ahern J. Male fetal loss in the U.S. following the terrorist attacks of September 11, 2001. BMC Public Health 2010;10:273. [20] Shils E, Young M. The meaning of the Coronation. Sociol Rev 1953;1: 63–81. [21] Grech V. The influence of migration on secular trends in sex ratios at birth in Cuba in the past fifty years. West Indian Med J 2014;63:6–10. [22] Grech V. The male:female ratio at birth is depressed by Maltese parliamentary elections and increased by other non-electoral events. Int J Trop Dis Health 2014;4:1123–31. [23] Davidson D. An adolescent in search of her identity. J Anal Psychol 1985;30:339–46. [24] Denney C. Representing Diana, Princess of Wales: cultural memory and fairy tales revisited. Madison: Fairleigh Dickinson Univ Press; 2005. [25] Grech V. Soccer World Cup influences sex ratio at birth. Eur J Sports Med 2014;2:21–9. [26] Mason T. Passion of the people? Football in South America: Football. New York: Verso Books; 1995. [27] Bousfield A, Toffoli G. Fifty years the queen: a tribute to her Majesty Queen Elizabeth II on her golden jubilee. Toronto: Dundurn; 2002. [28] Grech V. Economic stress and the secondary sex ratio: Ireland, Iceland, Greece and Latvia. Int J Trop Dis Health 2015;5:252–9. [29] Watson CW. ‘‘Born a Lady, Became a Princess, Died a Saint’’: The Reaction to the Death of Diana, Princess of Wales. Anthropol Today 1997;13:3–7. [30] Turner G, Bonner F, Marshall D. Fame games: the production of celebrity. Cambridge: Cambridge University Press; 2000. [31] Gilbert J, Glover D, Kaplan C, Bourne Taylor J, Wheeler W. Diana and Democracy, Special Issue, New Formations 36; 1999. [32] Catalano R, Bruckner T, Gould J, Eskenazi B, Anderson E. Sex ratios in California following the terrorist attacks of September 11, 2001. Hum Reprod 2005;20:1221–7. [33] Hawton K, Harriss L, Simkin S, et al. Effect of death of Diana, Princess of Wales on suicide and deliberate self-harm. Br J Psychiatry 2000;177:463–6. [34] Guerrero R. Association of the type and time of insemination within the menstrual cycle with the human sex ratio at birth. N Engl J Med 1974;291:1056–9. [35] Harlap S. Gender of infants conceived on different days of the menstrual cycle. N Engl J Med 1979;300:1445–8. [36] Gray RH. Natural family planning and sex selection: fact or fiction? Am J Obstet Gynecol 1991;165:1982–4. [37] Grech V. The influence of the Chinese zodiac on the male-to-female ratio at birth in Hong Kong. J Chin Med Assoc 2015;78(5):287–91. [38] Bonde JP, Wilcox A. Ratio of boys to girls at birth. Br Med J 2007;334:486–7.