I know this is very loose and subjective, but in your many years of experience and observation, just roughly one in how many people who are under some coaching scheme advances to pro level? Pro level can be one who competes in tournaments often and are likely to win, represent their state, or even country. I know that most people train and get frustrated after months of running drills and not being trained the main course and quit. Some expects to see instant results but ended up feeling disappointed and quit because of their unrealistic and overly demanding expectations. It will be frustrating for coaches as well to see that only one in, say 20, 30 or even 100 students stay on for years before turning pro.
For people who train seriously past 18 y/o, I think it's a very small number. Most people who turn pro are usually junior nationals who train at around 10-12 y/o. Badminton is very, very, VERY difficult to master in terms of both technique and physical conditioning.
I think it also varies between countries as well. In China, there's Millions of others who wants to be the next Lin Dan or Zhang Ning, but it seems that only about 10-20 individuals are selected to the national teams each year. So the ratio is like 1 in 100,000.
Depends on the emphasis that the country puts on sport development from the early ages at school. For sports in general Indonesia can only manage 22 people at the 2008 Olympics whereas Australia had around 480 people. Our country although small in population puts a lot more emphasis and money into sport. In Australia I believe that if we got a high level of coaching and more interest in the sport 1/100 people that committed to training beginning at a young age could have what it takes to become an advanced player. In Indonesia where schools don't teach basic coordination at a young age (I know my wife lived and went to school in Jakarta) I believe 1/1,000 would have what it takes to become advanced. It's like learning a language, it's easy to learn when you're young. Only a gifted few can pick up the skills when they're older!! Tim H