Working Group on Methods of Fish Stock Assessments (WGMG)
reportposted on 2009-01-01, 00:00 authored by ICESICES
Shrinkage (either by year or by age) is a relatively ad hoc device that was imple‐mented in the XSA model to try to reduce unwanted assessment fluctuations driven by noise rather than signal. We summarize the history of shrinkage in XSA and con‐sider how shrinkage is being used in current ICES assessment working groups. We conclude that a) shrinkage should where possible be “light”, and b) what “light” means needs to be determined by reference to estimation weights (rather than poten‐tially dubious metrics such as retrospective bias). More generally, we should turn to models that use data (rather than ad hoc assumptions) to generate inferences.
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