Sampling on successive occasions to re-estimate future asset management expenditure

Sampling schemes are used by the utilities such as electricity and water to assess the condition of their networks, and hence to predict future expenditure. Frequently the assessment process has to be carried out on a regular basis, e.g. every 5 years. However there is little published literature to provide guidance as to how much resampling to undertake, how to use the extra information gained and how accurate the results are likely to be. Therefore this paper describes simple linear and quadratic regression models for predicting future condition and investigates their performance. As this investigation requires all items to have a full condition history, a deterioration model is developed to generate this information.