In their books Hard Facts, Dangerous Half-Truths and Total Nonsense, Jeffrey Pfeffer and Bob Sutton argue that leadership is not all it's cracked up to be. They show how change at the top has little correlation with corporate performance and they make the point that leadership might matter to some degree, but not as much as having good systems in place.

Still, you can't ignore the importance of leadership. Indeed, new studies show that the private lives of CEOs have a huge impact on shareholders.

Research shows that following the death of a child, profitability was roughly 21 per cent lower in the two years after the tragedy. The impact was even more acute if the child was younger than 18. The death of a parent was correlated with a downturn but not as much. Interestingly, the death of a mother-in-law was followed by an upturn, although this was too small to be statistically significant.

The question is whether these findings apply to large US corporations given that most of the companies in the study were small and family-controlled.

Still, it might give shareholders a reason to check the death registries.