def versions_average_for_attribute(att, opts={})
      _use_delta = opts[:delta] || false
      if _use_delta
        return historical_rate_per_day(att, nil, nil)
      else
        data = versions_complete_data_for_attribute(att, opts)

        return data.e_mean
      end
    end
def versions_average_for_attribute(att, opts={})
      _use_delta = opts[:delta] || false
      if _use_delta
        return historical_rate_per_day(att, nil, nil)
      else
        data = versions_complete_data_for_attribute(att, opts)

        return data.e_mean
      end
    end
returns Float
 this is wonky because of the wonky way we use historical_rate_by_day