Restricting range restricts conclusions
THE EXPERTISE APPROACH AND SKILL ACQUISITION Research on expertise is by definition focused on a restricted sample of individuals. Experts are people who consistently produce outstanding performance in their domains (Ericsson, 2006) and as such are without exception located on the positive side of the skill distribution. The usual approach in the study of expertise is to compare the extreme group of the skill distribution, experts, with the extreme group at the other end, that of novices. This contrasting approach, which we have called the “expertise approach” (Bilalic et al., 2010, 2012), has a long tradition (Chase and Simon, 1973; Simon and Chase, 1973; De Groot, 1978; Preacher et al., 2005). Its main advantage over the common approach in cognition, where all participants are at the same skill level, is the presence of a control group of novices that enables falsification of results obtained on experts (Wason, 1960; Kuhn, 1970; Campitelli and Speelman, 2013). In that way, the expertise approach is not unlike the neuropsychological approach that contrasts results obtained on patients with the results of “normal” participants (Shallice, 1988). The main goal of the expertise approach is to provide evidence relating to the cognitive and neural mechanisms behind processes such as object and pattern recognition, which would be difficult to obtain from subjects who possess approximately the same level of expertise. The skill acquisition process, which is one of the main topics of expertise (William and Harter, 1899), is of secondary importance in the expertise approach. This is understandable as the contrast between experts and novices captures only the beginning and the end product of the skill acquisition process. It is unrealistic to follow people for the length of time required in order to achieve expertise in a given domain. However, expertise researchers have recently started employing an archival approach that provides a more complete picture of the skill acquisition process (Charness and Gerchak, 1996; Chabris and Glickman, 2006; Howard, 2008, 2009; Bilalic et al., 2009). In the game of chess, a domain commonly studied in expertise research, there are precise records of all practitioners from an early age (Howard, 2006a; Bilalic et al., 2009). These records include not only personal information such as gender and age, but also skill levels at different stages, numbers of games played, and corresponding skill change. The records provide a wealth of data for investigating the influence of factors such as age, gender, and even talent, on the skill acquisition process. Here we want to draw attention to the fact that some of the databases used in previous research only provide records of the very best practitioners. In the expertise approach, such restriction is an integral part of the methodology, but restricting the range of population in the archival approach could have grave consequences for the conclusions about the nature of skill acquisition.