Relationship Between Practice and Performance in Sports: A Meta-Analysis (2016) [pdf]

A good analogy is that expertise is like an area of a rectangle: Both innate factors and practice contribute to it.

Which contributes more? It depends on the variance on each dimension. We see from Fig 3 (page 9) in the paper that the unexplained variance is highest for elite athletes at 99%. Why? Because almost all of them practice as much as it is useful to do so. In other words, the heights of their rectangles are about the same, almost all of their area differences depend on other factors [1]. For other groups, the variation in practice time explains more about their performance differences.

[1] These may include innate talent, techniques, psychological factors, etc. With more than two dimensions, we may need to change the analogy which I do not have the time to get into now. Also, as with most analogies, it is not perfect. Practice time is likely not independent of talent.

Money quote on page 345: "In the second study, Mosing, Madison, Pedersen, Kuja-Halkola, and Ullén (2014) had over 10,000 twins representing an extremely wide range of music skill estimate deliberate practice and perform tests of music aptitude. Mosing et al. (2014) found that there were genetic effects on both music practice and music aptitude. More important, there was no evidence for a causal influence of music practice on music aptitude. Identical twins differing massively in amount of deliberate practice did not differ significantly in music aptitude."

Apologies for being contrarian, but let me flip things around: Perhaps people who are able to benefit from practice enjoy it and tend to do more of it.

I get excited learning about the latest C++17 features and used to love reading stock exchange specifications, which most people would find about as exciting as a root canal. I find it rewarding because I can apply what I learned and feel a sense of satisfaction. Conversely, I've always sucked at golf and could barely stomach the half-dozen lessons I tried, even though I consider myself a diligent person and spent years practicing many other things. I never improved my swing and the entire experience was nothing but frustration. If you have a rough time at a beginner or intermediate level, it's hard to gin up the desire for continued practice beating your head to a wall.

The premise of this paper is naturally enticing. If you had only tried a bit harder practicing lay ups in gym class, you could be just as good as Michael Jordan (ok more like you could get a bit closer, since they claim practice explains ~20% of results). I don't really buy it.

Anders Ericsson has replied to this meta-analysis [1], which in turn got a reply from McNamara et al [2].

In Ericsson's opinion/definition [1], deliberate practice is "individualized practice with training tasks (selected by a supervising teacher) with a clear performance goal and immediate informative feedback was associated with marked improvement"; and he argues "In contrast, Macnamara, Moreau, and Hambrick’s (2016, this issue) main meta-analysis examines the use of the term deliberate practice to refer to a much broader and less defined concept including virtually any type of sport-specific activity, such as group activities, watching games on television, and even play and competitions. Summing up every hour of any type of practice during an individual’s career implies that the impact of all types of practice activity on performance is equal—an assumption that I show is inconsistent with the evidence."

McNamara et al reply saying that evidence only accounts for a relatively small fraction of expert performance [2]: "we found that deliberate practice accounted for a sizeable amount of variance in sports performance (18%), but it left a much larger amount unexplained. Ericsson’s (2016, this issue) evaluation of our research is undercut by contradictions, omissions, and errors." They conclude that "The available evidence indicates that deliberate practice, though undeniably important, does not largely account for individual differences in expertise. Building on Ericsson’s pioneering work, the task now is to develop theories of expertise that include multiple factors."

[1] Summing up hours of any type of practice versus identifying optimal practice activities: Commentary on Macnamara, Moreau, & Hambrick (2016) http://journals.sagepub.com/doi/abs/10.1177/1745691616635600

[2] How Important Is Deliberate Practice? Reply to Ericsson (2016) http://journals.sagepub.com/doi/abs/10.1177/1745691616635614

This was a pretty interesting read, and something I've often wondered about. I remember when LeBron James joined the NBA. It just baffled me at the time how some 18 year old high schooler could be so much better than professional players, players who've played day in and day out for _years_. Hours of deliberate practice didn't seem to be an adequate explanation.

TLDR;

The 10,000 hr practice myth has long been busted by series of studies and this meta study is another one in the series focusing on sport. It turns out that among non-elites, only 18% of performance difference can be attributed to deliberate practice! More surprisingly, there are significant non-elites who spend same or more hours in deliberate practice which means that simply looking at this number doesn't allow you to accurately distinguish between elites and non-elites. Finally, starting at childhood has minimal advantage in performance difference.

This is another big stab in the nature vs nurture debate. There are many studies (also cited in this paper) which has indicated that deliberate practice only account for 30% of performance difference in activities like chess requiring purely cognitive abilities. So for physical activities, it makes even less difference! The paper has extensive references at the end which indicates that rest of the majority of differences comes from genetics and possibly psychological factors such as confidence, sensitivity to rewards, ability to focus, performance anxiety and so on.

So currently, it looks to me nurture contributes 1/3 and potentially (this is not in paper) nature another 1/3 and psychological factors another 1/3.