From Michael Barone at National Review- Equality at the Expense of Prosperity:

“There’s a persistent tension,” writes Bloomberg’s Clive Crook, “between the limits of the data [Piketty] presents and the grandiosity of the conclusions he draws.” Like global-warming alarmists, he extrapolates from abstract theory and a few years’ trendlines out a century forward — and presents the results as inevitable. He also presents them as justifying the confiscation, more or less, of wealth accumulated by private individuals and putting it in the hands of mandarins guided by their supposedly superior sensitivity to public welfare. There might be less inequality in such a world, but also less economic growth and a lower, though more equal, standard of living.


Research is often contaminated by the bias of a predetermined conclusion supported by selectively extracted facts.  Excessive data often creates a pattern that does not effectively extrapolate into an effective longer term conclusion.