Taxonomy of Stock Market Indices
  We investigate sets of financial non-redundant and nonsynchronously recorded time series. The sets are composed by a number of stock market indices located all over the world in five continents. By properly selecting the time horizon of returns and by using a reference currency we find a meaningful taxonomy. The detection of such a taxonomy proves that interpretable information can be stored in a set of nonsynchronously recorded time series. 
Giovanni Bonanno, Nicolas Vandewalle and Rosario N. Mantegna