DATA-ANALYSIS OR SIMULATION-MODEL - A CRITICAL-EVALUATION OF SOME METHODS

The use of regression, ordination and dynamic ecosystem modelling in l imnology is discussed by evaluating some of the vices and virtues of t hese techniques. Both general characteristics of the approaches and a few examples are used to stress the importance of analysis of the resi duals for evaluation of the models. Not completely unexpected, a simpl e ordination model did not perform worse than a complicated ecosystem model, both applied to the same lake system. Both models are shown to fail for prediction purposes, mainly because the error variance in the data used for parameter estimation is large compared to the variance that can be explained. Integration of regression, multivariate analysi s and dynamic ecosystem modelling, all followed by analysis of the res iduals, is advised. Nested models are proposed as a solution for the p roblem of changing parameters and for the problem of parameters being different among lakes.