For badminton, in a family of more than one child, generally speaking, who will become the better player? Eldest, middle, younger/est?
Usually not the oldest although that isn't always the case of course. Think about it, parent puts a child into a sport, they enjoy it get good at it, parents have more children and start the kids at that sport at an earlier age than before. If they take to the sport then they always have an older, better sibling to practice and improve with, eventually they overtake their older siblings and become better players. Look in Tennis for example, William's sisters, also Murray Brothers. Jamie Murray was the better junior player (ranked #1 in the world at one point) but Andy turned out to be the better singles player in the end.
just to go as a counter example to LD - adam/ben hollioake (cricketers) - the elder, adam, was the better player. footballing example: rio/anton ferdinand. the elder, rio, is the better player. bobby/jack charlton. the younger, bobby, was the (slightly) better player american football - eli/peyton manning. peyton is older and better.
You could argue all you want on generalities. 'Oldest has independence and confidence'. 'Youngest has older siblings with whom to practice'. Etc, etc etc. But what it really comes down to is temperament, not birth order. We are all born with certain personality traits. These are affected by our environment and upbringing. It is the final product from that which decides who will be the better athlete. I know in my household, we could tell the youngest was going to be the athlete... before he could even walk! What's this all about, venerable Cheung? Do you have only enough money to invest in lessons for one of your kids?
I am not aware of peer reviewed research articles on the subject of siblings and sport. If you know of any such social/sports studies, please reference them here. The most well known badminton examples are the Sidek brothers. The youngest didn't go to the heady heights of the elder brothers.
Hmmm... let's ask Toby when he has finished that little job he's on right now... And what about Rexy Mainaky and his brother Richard? And WMC and her sister? And LCW and his brother? Offhand, I'd like to say one of the younger siblings, but often not the eldest. The eldest will tend to assume responsibility to encourage and support a younger sibling in pursuance of a pro sport if the youngester shows talent and promise.
Saurabh and Sameer Verma are both on the international circuit, both quite young, although Sameer is the younger by a couple of years. Chris seems to feel that Sameer has more potential, although this has not yet been borne out. What about twins like Iris & Rena Wang? Or the brothers who used to represent USA in tennis? It would appear twins in pro sports sink or swim together...
Bob and Mike Bryan are the tennis players you're referring to. And they're actually still representing the USA and are almost always ranked 2 or 1 in the world. They're identical twins though, so in this case they don't exactly apply =).
I sincerely hope that this is a hypothetical question. It would be wrong on so many levels to apply this in practice. Could you imagine the hurt that would be inflicted by continuously telling one sibling that they must be the best player or that they'll never be the best player? What useful conclusion could be drawn from such studies?