One thing to consider when looking at your statistics on distance gains is that despite the trend toward lengthening courses, the biggest hitters may still be bumping up against the length limits of the architecture, and they may be using more 3 woods even on the measured driver holes. (I tried to look into this a bit a while back and it seemed to me that there has been a drop off of driver use among the long hitters but I don't have full access to the PGA stats so it is difficult to determine.) If this is correct, then the Tour driving stats would understate the gains due to technology. For example, it looks to me in 2013 Dustin Johnston only hit driver on about four of every seven "measured drive" holes where the Tour collects advanced launch stats. If so, then in reality his actual driver distance may have been quite a lot longer than his measured driving distance, since three in seven of his "measured drives" may have been hit with a club other than driver.
That's a good point, but the interpretation is a little more complicated. If more and more players are hitting three woods off the tee on the "measured drive" holes, this would cause both the overall distance gains and the within-player gains to decrease. It might lead us to understate the effects of technology (especially if we think that 3 wood technology lags behind driver technology), or it might lead us to understate the differences between new players and retiring players.
I truly find your graphs hard to believe. Your graph says that player physical capabilities were on a decline from 1990 to 1993, then miraculously were responsible for 20 yards of increase for the next 10 years, followed by them getting fat and lazy and having their physical capabilities decline again.
I see what you mean, but the declines are pretty small (a few yards). That could be attributed to changes in the courses, setup, conditions, or player strategy (more players hitting 3 woods off the tee as David points out). I wouldn't want to overanalyze any small change on the graph, but the general finding is that the within-player gains in distance are not nearly as great as the overall gains. That suggests to me that player replacement accounts for about half of the distance increases, while technological changes can, at most, account for half.
Did you also account for the fact that the same players are a year older each year and are on average going to be weaker than they were the year before? The effect might not matter aging from 24 to 25, but it would from 34 to 35 and even more from 44 to 45.
Yes. In generating these estimates, I have controlled for the players time on tour in a flexible way (by including dummy variables for each additional year on tour). This turns out to not matter at all. After accounting for overall trends coming from technological changes and other factors, players do not appear to systematically get longer or shorter as they age on tour. Of course, at some point, we'd expect players to eventually lose distance with age, but for the vast majority of players, this doesn't happen until they're already off the tour.
December 2003, State of the Game program on the Golf Channel.
"The biggest reason for distance increases in the last two or three years, not the last ten, starts with the Tour player finding out how to maximize launch conditions" Taylor Made CEO Mark King
He continues, "Higher launch, less spin, speed is the same, the ball goes 20 yards farther". ... "That isn't the face [of the club], that isn't the length of the shaft. That isn't how strong the guy is."
Frank Thomas book Just Hit It points out that high handicappers do not benefit from the distance gains, because they don't find the sweet spot very often. He does conclude that high MOI is beneficial to the high handicapper, but at one point in the book he admits that benefit is marginal.
I wouldn't go to the CEO of Taylor Made for an unbiased assessment of the effect of new driver technology. Of course, he'll tell you that they're new drivers help you hit it further. My speculation regarding greater gains for high handicappers was made precisely because they don't hit the sweet spot all the time. It's hard to increase distance for players that hit the sweet spot every time (especially since the COR is limited). Alternatively, if you can increase the sweet spot, you could considerably increase the average distance of high handicappers. Obviously, you won't increase their maximum distance much, but you'll bring up the average by making their misses better.