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With his book "Outliers" Malcolm Gladwell has widely popularized the idea that the requirement to become an expert in any field is largely to invest at least 10.000 hours of deliberate practice.

  1. What is the scientific basis of this conclusion?
    It seems to have originated from this research by Ericsson et al. (1993). In what way does this paper support the conclusion of a 10.000 hour rule?

  2. What is the current state of the research on this question?

Reference

Ericsson, K. A., Krampe, R. T., & Tesch-Römer, C. (1993). The role of deliberate practice in the acquisition of expert performance. Psychological Review, 100, 363–406. doi:10.1037/0033-295X.100.3.363

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    $\begingroup$ This isn't a peer-reviewed source, but it gives a digestible overview of the limits to the "10,000 hour rule": slate.com/articles/health_and_science/science/2014/09/… $\endgroup$ – blz Mar 27 '15 at 12:16
  • $\begingroup$ Haha, I didn't see this was written by Hambrick. He makes very good points, but he really has a bone to pick with deliberate practice for some reason. $\endgroup$ – Christian Hummeluhr Mar 27 '15 at 15:21
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The answer is more involved than it seems. Expertise research programmes, including Ericsson's line, has tended to blend quantitative and qualitative research methods (e.g., case studies, talk-aloud protocol, etc.), and there is a veritable host of critiques and qualifications that apply. For the scope of this answer, I will therefore try to err on the side of too restrictive than too broad.

10,000 hours?

The 10,000 hours figure, supposing that you are right to pin Malcolm's work on this article, appears to derive from an analysis of retrospective practice accounts of violinists. In any case, from the article, page 379.

"The number of hours of practice accumulated by a violinist at a given age can be easily calculated by adding the yearly estimates at and below that age. The average number of hours of accumulated practice for each of the four groups is shown in Figure 9 as a function of age."

figure9

In my experience, rather than giving the 10,000 hours figure, Ericsson himself instead often proffers 10 years, as he does in the abstract of this article. This is more consistent with recent research on effects like spaced repetition and the generation effect, since using hours seems to imply that hours of deliberate practice are interchangeable and independent, which they are evidently not. I don't know if it's meaningful to give a year value, but I subjectively doubt it.

Is deliberate practice effective?

I will interpret the second question as, "What is the state of research on the training efficacy of deliberate practice?" instead of the alternative meaning about 10,000 hours, which I have argued is flashy, but not meaningful or central to expertise acquisition.

Deliberate practice has been studied and compared with traditional training and educational methods fairly extensively across a number of domains. Here, I will restrict myself to studies dated 2011-2015 which were not published by K. A. Ericsson himself. I found a convenient meta-review of 14 studies, which found deliberate practice combined with simulations to be effective for clinical training (McGaghie et al., 2011), the area in which deliberate practice sees the most use by far.

Multiple recent studies have taken a critical view of Ericsson's strong theory of deliberate practice (i.e., performance is a monotonic function of deliberate practice), but no one appears to seriously dispute that it is a substantial factor in expertise acquisition for some domains. A critical meta-analysis of deliberate practice by Macnamara, Hambrick and Oswald (2014) reported:

"We found that deliberate practice explained 26% of the variance in performance for games, 21% for music, 18% for sports, 4% for education, and less than 1% for professions."

Concluding remarks

For the purpose of this question, I would say this: on the one hand, the number of hours is meaningless and more likely than not to vary substantially between domains, persons and situations. The 10,000 hours figure is therefore only illustrative, not practically meaningful.

On the other hand, there is evidence to support the efficacy of deliberate practice as a learning strategy. Finally, though it remains influential, recent research suggests that deliberate practice alone is not sufficient to explain expertise acquisition, and that interacting factors need to be considered.

Despite the waning star of strong-form deliberate practice theory, I thoroughly recommend Ericsson et al.'s Cambridge Handbook of Expertise and Expert Performance (2006) for an introduction to this increasingly relevant area of psychology. Personally, I think the recent studies finding that deliberate practice doesn't seem to predict anything in some domains are absolutely fascinating, but I can only speculate as to why.

References

  • Ericsson, K. A., Charness, N., Feltovich, P. J., & Hoffman, R. R. (Eds.). (2006). The Cambridge handbook of expertise and expert performance. Cambridge University Press.
  • Macnamara, B. N., Hambrick, D. Z., & Oswald, F. L. (2014). Deliberate Practice and Performance in Music, Games, Sports, Education, and Professions A Meta-Analysis. Psychological science, 25(8), 1608-1618.
  • McGaghie, W. C., Issenberg, S. B., Cohen, M. E. R., Barsuk, J. H., & Wayne, D. B. (2011). Does simulation-based medical education with deliberate practice yield better results than traditional clinical education? A meta-analytic comparative review of the evidence. Academic medicine: journal of the Association of American Medical Colleges, 86(6), 706.
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Ericsson doesn't emphasize on the precise number of hours needed to be a world-level expert. What he emphasizes is the importance of deliberate practice in gaining expertise.

BTW, Macnamara et al.'s meta-analytic research has some severe weaknesses. For example,

  • Not representative : They categorized the previous researches into 5 domains -- sports, games, education, professions, and music. For instance, in the professions domain, they concluded that DP explains 1% of variance in performance. However, the more carefully you look into their research, the more you will be surprised. The professions domain includes only 4 researches. Researches about soccer referees, pilots, insurance sales agents, and computer programmers. Even more the sample size for each effect size in that domain doesn't go over 100. For games domain, there are 8 researches and the six are about chess and the rest two are about scramble. I don't think it can represent something like "professions" or "games".
  • Not balanced : If a paper included multiple effect sizes for different samples (for example, the study divided the sample group into ages), their research treated each one as significant as any other effect sizes from different papers. The problem with this is it could be biased by that particular research setting and method. For example, in the education domain, the total number of effect size analyzed here is 51, and almost half of them came from just two papers. How they defined and measured the deliberate practice and performance in those studies might have had a bigger influence to the result of the meta-analysis.
  • Loose definition of performance and deliberate practice : The definitions of those two were not strictly following what Ericsson has emphasized. For example, in the study of pilots, they considered flying hours as deliberate practice hours. And in the study of computer programmers, they considered job level as performance -- it has been already shown job level is not a good predictor for performance. Also, in the study of soccer referees, they asked the referees to recall the accumulated hours of deliberate practices, and moreover, their definition of deliberate practice included running and flexibility trainings, and even sauna times, whereas the performance was perception and judgment test like foul and offside assessments. You see they measured and compared so remotely related things.

There are more to point out, but I will stop here and let you read it and think yourself. Their research data is open at https://osf.io/rhfsk/ and their methodological details are at http://pss.sagepub.com/content/suppl/2014/07/01/0956797614535810.DC1/DS_10.11770956797614535810_SupplementalMethodsandResults.pdf

Recent researches in deliberate practices has been focusing on the quality of deliberate practices and I am more interested in this area.

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