The sentiment classification column represents ranges within the sentiment index (SI) indicator.  Those ranges are documented in the whitepaper and represent different interpretations for SI depending on which range it is located.  For example, a SI less than -1 has a different meaning from an SI that is between -1 and 0. SI also has a different meaning when it is a positive value.  Because the interpretation of SI changes depending on its value, the sentiment classification column provides a convenient way of qualifying the SI value. This qualification should be incorporated into your trading strategies.