ABSTRACTThe location of tributary drainage basins nested within higher order systems forms the basis for a proposed classification into order-formative and order-excess subsystems. The significance of these order types in generating distinctions within an order level is examined with a battery of twenty-five network parameters sampled over two contrasting geomorphic environments. The contribution of the order-type effect is found to vary with parameter and data set. Empirical analyses based upon samples of drainage networks defined solely by stream order level are of doubtful interpretation where this variance contribution is ignored.