Expertise in ill-defined problem-solving domains as effective strategy use.

Expertise consists of many different cognitive structures. Lemaire and Siegler (1995) have proposed a four-layered account of expertise from a strategies perspective: Experts have better strategies, tend to use strategies that are better overall more often, are better able to select the circumstances to which a strategy best applies, and are better able to execute a given strategy. Originally, this account came from work in simple, well-defined domains. We explored this account in the complex, ill-defined domain of platoon leadership. In Experiment 1A, we elicited free-text responses to leadership scenarios from novices, intermediates, and experts, finding expertise effects for strategy base rates and choice, but not for strategy existence or the number of strategies used. In Experiment 1B, we used a new group of experts to gather ratings of the execution accuracy of the responses in Experiment 1A and found expertise differences in the ability to execute the same strategies. We propose several elaborations to the original four-layered strategies account of expertise on the basis of these results.