all it takes is 1 billionaire with interest incum of $6.9m a year to skew the average. if billionaire has investment incum or returns of $69m per year it will skew it more to the high side. add 69 billionaires earning $69m each per year on investment returns alone, it will skew the average more. for more useful and realistic calculations they need to remove the top 0.69% outliers.