Leadership, as you may already in know, is a rather complex phenomenon. But what you should also know is that great amount of money is spent by companies to hire leaders, train/develop them and deal with them should they not perform. Of all costs the latter is the greatest and is seldom accurately reported.
In this summary of research we briefly discuss the science of predicting leadership emergence and effectiveness. An emergent leadership is a very different from effectiveness model of leadership. However, this difference is not the scope of the article.
Intelligence
Better described as general cognitive ability, intelligence is a great predictor of leadership. In fact of all psychological factors g can predict leadership emergence the best (r=0.4). Ability to work with complexity, think about future, build scenarios, learning things quickly and solving problems on the fly are all much needed competence in a leader and g predicts just that. Needless to say g alone is not a mark of a good leader, but from statistical point of view, g predictss leadership the best.
Personality
Personality is a good predictor of job performance. Leadership requires different behaviours at different instances. The ability to exercise one's traits is a mark of good leadership. However, a great deal of research has proven that conscientiousness, neuroticism and openness to idea are all good predictors of leadership emergence. Extraversion and agreeableness have mixed results. Surprisingly, agreeableness has been found to have negative correlations with leadership emergence and positive correlations with effectiveness.
Handling Stress
Leaders are less impacted by stress. And the proof is irrefutable. Biological evidence from cortisol level (stress causing hormone) suggest that the basal levels of cortisol in leaders are higher. Which entails that leaders are used to high stress and their cortisol levels do not increase much with stress. Emotional stability factor from personality also has positive correlations with leadership emergence. Hence, ability to not be perturbed by stress is also a sound predictor of leadership capability.
Emotional Intelligence/Ability
While studies show that EI predicts leadership effectiveness, EI itself is highly correlated with g and big 5 factors. Hence , from psychometric standpoint it doesn't offer any additional insights into leadership capability. Alarmingly, some studies have shown that high EI leads to lower leadership effectiveness.
Creativity
Creativity both in terms of a trait as well as ability is a strong predictor of leadership effectiveness and not emergence. Surprisingly this is true across industries and sectors. This could be a reflection of the fact that strategizing and exploring new avenues of growth do require creativity.
In all, psychology has enough insights into what would make a great leader. Furthermore, definitions of what effective leadership looks like across cultures is similar. This doesn't mean that culture has no impact on leadership. Adequate evidence exists to suggest that socially acceptable leadership behaviours differ from culture to culture. E.g. in US a good leader is expected to be an extrovert while in Japan a good leader is culturally perceived to be introverted. That said, a great amount of leadership can be scientifically predicted with analytical models which are customised to an organization, industry and culture.