Mark Shepherd, David Wheeler, Diana Selbie, Laura Buckthought & Mike Freeman
AgResearch Ltd, Ruakura Campus, Hamilton
When debating the performance of models such as Overseer‟s ability to estimate whole-farm nutrient losses, four terms are often used almost interchangeably: accuracy, precision, error and uncertainty. However, the terms are not interchangeable and it is important to consider the implications of the commonly used terminology, in the context of this farm-scale nutrient budgeting model.
Given that it is not usually practicable to directly measure whole-farm nutrient losses, use of the terms accuracy or error are not directly applicable, because there is no true value to compare an estimate with.
Model uncertainty is the most relevant applicable term for annual whole-farm nutrient loss estimates. Model uncertainty will be greatest for conditions where there are no, or few, data for calibration and validation. Precision in the context of Overseer is about precision of input information.
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