A Parameter-Bounding Approach to Sensitivity Assessment of Large Simulation Models

Traditional sensitivity assessment (SA) methods have limitations which motivate a new approach, the subject of a new project at ANU and the Universities of Adelaide and Melbourne, with the Murray-Darling Basin Commission and the South Australia Dept. of Water, Land and Biodiversity Conservation as partners. The limitations include high computing load, restricted scope and validity of the results, excessive volume of results and failure to distinguish SA from uncertainty assessment. The new approach has three main aims: (i) to investigate sensitivity of a wide range of model outcomes, not only the values of individual output variables; (ii) to examine sensitivity to changes which are not small; (iii) to find efficiently features such as critical or nearredundant parameter combinations. Requirements such as output ranges, credible behaviour or given rank order of scenario outcomes define an acceptable outcome set. SA then explores the feasible set of parameter values producing acceptable outcomes. This inverts the mapping by the model from parameters to outcomes.