code: def _calculate_bias(self):
          
          for m in self.metadata:
              for b in self.bias_details:
                  if  b[0] == 'bias-' + m['label'] + '.csv':
                      l_bias = 1.000
                      try:
                          l_bias = float(b[2]) + 0.5
                      except:
                          lg.record_process('bias.py','ERROR converting bias value to float: ' + str(b))
                      self.bias_rating *= l_bias
docs: returns a weighting from 0 to 1 based on the sources.
          Due to fractions multiplying resulting in very small 
          numbers, adding 0.5 to bias calculations which means
          actual range is 0.5 -> 1.5 (still testing)
          
          Note - range should be from 0 - > 1