Several studies have shown that the more complex the job, the greater the difference between a superior performer and an average one. For example, a routine blue-collar worker who is a standard deviation above the mean would be 20% more productive than the average worker. The figure to the right shows the typical bell-shaped normal distribution of performance for simple jobs.

A worker in a more complex job (a life-insurance salesperson, for example) who is one standard deviation above the mean would have a level of performance that is 120% higher than the average. For jobs of even higher complexity (an account manager of a consulting firm, for instance), one standard deviation could represent an increase on the order of 600% over the average. The figure to the right illustrates how this performance spread grows exponentially with the complexity of the job.

The performance spread offers substantial potential rewards. As shown in the figure to the right, companies that are able to identify and appoint top performers to senior positions will achieve a level of performance several times higher than that of firms with the most frequent executives. Put another way, organizations that hire or promote mediocre executives will suffer greatly from the relative incompetence of those individuals.