code: def _factory(slice_, axis, weighted):
          
          if slice_.dim_types[0] == DT.MR_SUBVAR:
              return _MrXCatPairwiseSignificance(slice_, axis, weighted)
          return _CatXCatPairwiseSignificance(slice_, axis, weighted)
docs: return subclass for PairwiseSignificance, based on slice dimension types.