A star is born - mostly in January

Relative age has a bigger effect in contact sports, but there is still a correlation in other sports.

Statistics suggest babies born closer to age-group cut-off have better chance of sporting success.

If your own international rugby dreams have been thwarted but you want your son to one day pull on the All Black jersey, plan ahead and try for a January baby.

Boys born in the first three months of the year have more chance of making it to rugby's biggest stage, the Herald can reveal.

Of the 173 men who have debuted for the All Blacks since rugby turned professional in 1996, more than one-third (60) were born in the first three months of the year.

The next closest quarter is the third, July to September, when 39 were born.

The stats give credence to the theory of Relative Age, highlighted in Malcolm Gladwell's book about talent, Outliers. The theory is that those born closer to age-group eligibility cut-offs have an inherent advantage. They're picked for age-group teams not necessarily because they're more talented, but because they're older and usually bigger. This foot-in-the-door gives them access to better coaching and gives them exposure, so they improve.

Examples of January babies who debuted for the All Blacks during the professional era are Reuben Thorne, Aaron Cruden, Sam Cane and Luke Whitelock. Richie McCaw, born on December 31, has defied convention.

Relative age has a bigger effect in contact sports, but there is still a correlation in other sports.

The age-group eligibility cut-off for cricket is September 1. In the same 1996 timeframe, the biggest test-producing quarter is September-November, with 20 of the 67 test players being born in these three months. September Black Caps include Nathan Astle, Craig McMillan, Brendon McCullum, Martin Guptill and Jimmy Neesham.

The months to avoid if you want your progeny to chase glory? Only 10 May babies have become All Blacks since 1996, and just four have become test Black Caps.