In this week's Christmas issue of the BMJ, Michael Perkin, a child health specialist and father of three young boys, wrote to all 24 clubs in the Nationwide Division Three. Fourteen clubs replied, supplying siblings details of 232 players (23 goalkeepers, 72 defenders, 68 midfielders, and 69 forwards).
Family size varied significantly by football position. The average number of siblings of a goalkeeper was 1.1, defender 1.8, midfield 2.4, and forward 2.0. However, forwards were less likely, not more likely, to be eldest siblings.
One explanation for goalkeepers being from smaller families may be that in such families individual children spend longer in goal, whereas children in bigger families can rotate through other positions, suggests the author.
Overall, it seems safe to conclude that male siblings should not be dissuaded from adopting any football position that appeals to them, he says.