"However none of the work I've seen selects groups of individuals on a random basis and forces the various groups to practice different amounts of time to see that there is a correlation regardless of the individual."
There been studies that shows,
if you practice pattern AAABBBCCCDDD or pattern in this way, AABBDDCC and break the pattern up you get two set of results,
the group using AAABBBCCCDDD do really well if the pattern is consistent,(AAABBBCCC etc..) but as soon any random letter is trown in there, they do badly.
The group practising random patterns didnt do that well when it was presented with a simliar task as AAABBBCCCDDD but did well on similiar tasks that required random patterns.
Dan Inosanto a martial arts instructor used drills for one group and lot of sparring with another group.
Then he put them togheter and fought it out, there was no difference in ability between the different learning protocols.
Learning is contextual, which basically means, how you practice in the context also will show how you handle the real deal.
There is a time difference but also a quality difference depending on who is the teacher.
If one use whole form teaching, learning the whole movement, without for example swing thoughts, one learn faster.
This is due to the auditory cortex is left out of the learning curve in the context.
The auditory cortex can be activated outside the learning context for evaluation etc...
I teach dyslexic kids spell and write faster than anyone out there and I also are able to handle finemotoric functions of kids that dosnt talk that well. Then I use a proper feedback protocol that dosnt include debating - just pure feedback.
Now, that is why pro golfer use forged clubs, they get feedback from the shaft they then create images of.
If you ask them, they will tell you how it felt hitting that ball on the second groove.
They see the ball as they hit it.
Now, that is NOT possible, but they have learned to see the ball trough the sensation they get trough the shaft, similiar to the deaf who see sound bouncing off the walls showing the rooms texture.
Now, ask anyone teaching if they teach you to see the ball trough the shaft?
Why? It is what a profesional golfer actually does.
Now, if one practice,
the time spent, can either be a faster learning curve or a slower one. This is due to how intense the practice is as the brain activates more the more it has to focus and that is accomplished with intensity or overload.
The 10 year learning curve for expert performance is the result of todays teaching methods and protocol.
So the goler I teach, he gets this handicap golfer, and tells him some stuff, and suddenly he is pouring out the ball 50+ yeards more, he drops 10 shot of his normal scoring, and the guy cant belive it and his reaction is fear.
The result is to good to be true.
This happens when the individual is linking who they are with the learning and ability to perform at a specific level.
As it isnt tehr esult that is the issue, its how they see how good they are which is btw lower than the new score, they back down to a comfortable level, the old result.
This happens, so if one is to measure results, the variables one has to deal with are many.
Its not that easy to measure, the time spent vs the result as variables as the above will affect the result.
Things as, they dont belive the teacher, they dont belive its doable, they dont like the drills etc...
Whole-form teaching, is faster as the body moves the natural way in the motion required.
Any break down will be slower unless the whole-form motion is well practised and known and then one can break down to details and improve the motion.
But golfers are taught detail teaching which is the wrong way to do it, and yes, Bertholy was wrong.
Whole-form, spend time getting the needed proficient level, which is a feedback thing and then, you can do Bertholy and get a much faster and better result.
That is why some people on this forum, never will ever master the golf swing, they dont have the whole motion down.
That is a requried criteria if anyone ask me.
That is what young people playing golf learns, the whole motion.
That is how I teach my sisters kid.
whole motion first, and later, we break it down.