team level. Some theoretical research has developed models of the knowledge, skills, and abilities required of workers organized into teams but the association between individual trait characteristics and team performance generally has not been studied in actual field settings, with the exception of a few studies examining composition in terms of member ability. One reason is the difficulty of finding samples with an adequate number of teams. Another reason is that a focus on teams rather than individuals requires composition variables to be measured at an aggregated level of analysis. This higher level of analysis is often difficult because there is not an established theoretical approach for proper aggregation of individual characteristics into team-level constructs. There are a variety of ways in which team composition can be possibly turned into a measurable team characteristic. The common element of the methodologies involves first measuring characteristics of individual team members. The appropriateness of any operationalization depends largely on the nature of the task being completed by the team, the research questions being asked, and the specific traits being analyzed. However, in the absence of an explicit theoretical model of emergence to guide composition, “team personality” or “team ability” (or other such constructs) are of questionable construct validity and research may yield spurious findings. There has also been a relative lack of attention to the latent constructs that underlie variables of interest within research on team demographic composition. As a result, it is often difficult to determine precisely how or why variables such as team member age, tenure, or demographics influence team processes and outcomes. Recent research on team personality and cognitive ability composition has placed greater attention on understanding these underlying constructs; however, additional research is needed to identify the mechanisms by which team composition has its effects. Researchers have historically adopted three different methods for operationalizing team composition, which will be described below. Individual studies tend to report results for only one of the approaches; consequently, potentially important relationships between the various team-composition operationalizations and team processes and outcomes cannot be detected. Mean score For additive tasks the mean level of a trait may be most appropriate because these tasks are structured so that the contribution of each member adds to a collective pool that can be used to help the team succeed. The most common operationalization is to calculate a mean score for the individual measures. This approach assumes that