code: def calc_prob_mom(returns, other_returns):
      
      return t.cdf(returns.calc_information_ratio(other_returns),
                   len(returns) - 1)
docs: `Probabilistic momentum <http://cssanalytics.wordpress.com/2014/01/28/are-simple-momentum-strategies-too-dumb-introducing-probabilistic-momentum/>`_ (see `momentum investing <https://www.investopedia.com/terms/m/momentum_investing.asp>`_)
  
      Basically the "probability or confidence that one asset
      is going to outperform the other".
  
      Source:
          http://cssanalytics.wordpress.com/2014/01/28/are-simple-momentum-strategies-too-dumb-introducing-probabilistic-momentum/ # NOQA