Cognitive capacities (which include not only general intelligence but also elements such as reasoning) strongly correlate with various measures of leadership and leadership effectiveness across a wide variety of situations [1, 7]. Studies that specifically test intelligence consistently show higher performance by leaders, and this correlation stands as an independent factor when evaluated by multivariable analysis. In isolation, the correlation between intellectual abilities and leadership performance is imperfect. For example, in studies of military leaders, high intelligence was undermined under circumstances of high stress or emergencies [10]. General intelligence is most associated with leadership performance when linked with at least one other leadership attribute, and the association is stronger when more complex measures of analytical ability are factored in. Creative thinking appears to be a particularly important leadership trait in situations that require complex problem-solving [1].

The role of personality in leader emergence or leader effectiveness has been more effectively evaluated through the development of standardized frameworks such as the so-called Big Five model and Myers-Briggs Type Indicators [1]. All of the big five major categories of personality traits (Table 5.2) have been found to be associated with leadership to some degree [12].

Neuroticism (manifest as anxiety, insecurity, and sometimes irritability and hostility) negatively correlates with leadership [12, 13]. On the other hand, personality traits that reflect a low degree of neuroticism such as self-esteem are predictive of leadership. Extroversion is the strongest and most consistent trait that has been positively linked to leadership, whereas agreeableness shows the weakest correlation. Studies that have used Myers-Brigg indicators confirm the association with extroversion. However, studies of military leaders have shown preferences for sensing, thinking, and judging, whereas business executives may also show a preference for intuition, which may correlate with communication style [1]. Among the challenges of the study of leadership traits is observer bias: the ability to distinguish self versus observer ratings of personality [12]. Another challenge is that of attribution bias, in the sense that the personality traits of individuals are assessed through stereotypical assumptions about the characteristics of leaders [13].

Drive (which includes achievement, ambition, energy, tenacity, and initiative) has been emphasized as a particularly important leadership trait [3]. Motivation to lead appears to reflect a need for power or dominance. The extent to which motivation and drive correlate with leader effectiveness or leader achievement varies from study to study, and appears to be difficult to isolate from the impact of cognitive abilities and personality profile [7].

Social appraisal and interpersonal skills are particularly critical leadership traits [1]. Also known as social intelligence, the ability to understand and respond effectively to the feelings, thoughts, and behaviors of members of a group consistently correlates with leader emergence and leader effectiveness across a range of both military and civilian settings. Emotional intelligence is a related social appraisal and interpersonal skill that comprises self-awareness and self-control. Emotional intelligence appears to strongly correlate with leadership, leader work outcome, and subordinate work outcome.

The final category of leadership attributes is leader expertise and tacit knowledge. Practical intelligence, which by definition comes from experience, correlates closely with leadership emergence, but whether the ability to learn from experience is an innate or acquired leader quality has not been extensively investigated.