What Month Was My Tennis Player Born In?

Written by: Staff on 1st February 2012

What Month Was My Tennis Player Born In?

Li Na of China hits a return in her women's fourth round match against Kim Clijsters of Belgium at the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 22 January 2012. EPA/HOW HWEE YOUNG |

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About two years ago, the author heard about the results of a study saying that there was a correlation between birth month and success in certain team sports — baseball and basketball, if the author recalls correctly. (This was a radio program, so I didn’t really get to take detailed notes.)

This is sometimes linked with something called the “Gauquelin effect,” or the “Mars effect,” which is extremely dubious scientifically — it claims links with planetary positions, and in at least some of the cases cited, it has been shown that Gauqelin’s data did not demonstrate correlation.

However, the radio claim was not based on the “Gauquelin effect.” The explanation given was that sign-ups for various youth sports teams were based on ages, and players who were just a little older or younger would have significant advantages — they would get more playing time, or be the strongest on the team, or something. So let’s play with the idea anyway. Is there a tennis advantage?

We first looked at this at the end of 2009, and there was a curiosity: There were relatively few players born in November and December, and few top players born in January. We looked at it again in early 2011, and the results were somewhat similar. We now have a new Top Hundred. Has anything changed?

We must be cautious. We’re going to look at the birth months of the WTA Top Hundred (based on the rankings at the start of the Australian Open). Now suppose we were to find that (say) players born in September, October, and November were twice as common as those born in any other three-month period. Does this mean that being born in those months implies an advantage?

Not necessarily. It might be coincidence. Not likely with a ratio like that, but certainly not impossible.

It might have to do with the parents. The single best way to have kids who are great athletes, according to another, better study, is to have great athletes as parents. But consider this: In the case of outdoor tennis, the primary “down season” is the North American winter — roughly December, January, and February. Parents who themselves played tennis, and preferred to play outdoors, might play less in the winter months — and so, since they need, ahem, other recreational activities, might be more likely to conceive children in those months, and so have the children born in September, October, and November.

Or, of course, there could be an effect of the schedule of outdoor tennis clinics. Or… well, or almost anything. While we know what the results were for 2009 and 2010, we are deliberately writing this preface before we even know what the results of this will be for 2012, so we won’t produce speculations influenced by the data. Our next step, of course, is to take the WTA Top Hundred and determine their birth month balance.

January (total of 9): Peng (#17), Kirilenko (#29), Kerber (#30), Hercog (#35), Martic (#55), Dulko (#68), Parmentier (#70), Cornet (#85), Krajicek (#91)

February (total of 11): Li (#6), Jankovic (#13), Pennetta (#20), Safarova (#24), Vinci (#25), Cetkovska (#33), Zakopalova (#43), Benesova (#46), King (#66), Arvidsson (#75), Tatishvili (#83)

March (total of 11): Kvitova (#2), Stosur (#5), A. Radwanska (#8), Scheepers (#37), Zahlavova Strycova (#49), Morita (#52), Erakovic (#62), Mattek-Sands (#67), Dominguez Lino (#76), Oprandi (#80), Stephens (#95)

April (total of 10): Sharapova (#4), Hantuchova (#21), Gajdosova (#39), Errani (#48), Cirstea (#59), Dokic (#64), Brianti (#71), Johansson (#74), Arn (#92), Sevastova (#96)

May (total of 9): Cibulkova (#18), Peer (#34), Pervak (#40), McHale (#42), Hradecka (#51), Dulgheru (#61), Falconi (#81), Razzano (#84), Tanasugarn (#93)

June (total of 6): Schiavone (#11), Clijsters (#14), Kuznetsova (#19), Kanepi (#27), Petrova (#31), Makarova (#56)

July (total of 7): Wozniacki (#1), Azarenka (#3), Pavlyuchenkova (#16), Medina Garrigues (#28), Zheng (#38), Barthel (#44), Kleybanova (#89)

August (total of 7): Martinez Sanchez (#36), Begu (#41), Vesnina (#53), Baltacha (#54), Larsson (#60), Bondarenko (#88), Birnerova (#100)

September (total of 12): Zvonareva (#7), Petkovic (#10), Williams (#12), Lisicki (#15), Niculescu (#32), Pironkova (#47), Halep (#50), Suarez Navarro (#58), Keothavong (#73), Date-Krumm (#79), Daniilidou (#86), Barrois (#87)

October (total of 7): Bartoli (#9), Wickmayer (#26), Rybarikova (#69), Pous-Tio (#72), Dushevina (#82), Bremond (#94), Dubois (#97)

November (total of 5): Ivanovic (#22), Goerges (#23), Yakimova (#63), Soler-Espinosa (#78), Mayr-Achleitner (#98)

December (total of 6): Paszek (#45), Voskoboeva (#57), Marino (#65), Rus (#77), Jovanovski (#90), U. Radwanska (#99)

If players were born at random, we would expect to have 8 or 9 players born each month, and 25 in each three month period. Instead, we have 31 born in January-March, 24 in April-June, 26 in July-September, and just 18 in October-December.

This compares to the early 2011 figures of 29 born in January-March, 29 in April-June, 25 in July-September, and just 17 in October-December.

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