A comparison of Fuzzy, Bayesian and Weighted Average formulations of an in-stream habitat suitability model.

Three variations of a simple in-stream habitat suitability model were implementedand the effect on output for one organism at 22 sites on one short section of a river wasexamined. The model uses only two factors, depth and velocity, to calculate quality and a thirdfactor, width to quantify utility. The implementations were based on 3 multi-criteria evaluationapproaches: Weighted Average, Fuzzy Sets and Bayesian probability. There was broadagreement between the formulations but important differences in detail. The model outputsindicate that uncertainty arising from model formulation is significant and can have a bearingon planning decisions. There is a complex interaction between the formulations and thecharacteristics of the sites. Suitability models should be used thoughtfully and implemented inways that: facilitate exploratory analysis; present ranges of possible outputs; present indicatorsof uncertainty; and facilitate back tracking to explain the outputs.