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WP 3.3 ICES WGMG Zeros. ICES WGMG. Working Group on Methods of Fish Stock Assessments What does the other G stand for? Has been renamed Methods Working Group Met in Woods Hole 13-22 March 2007. Zeros Issue. Only addressed as a working paper Similar to WP 3.1 from this meeting
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ICES WGMG • Working Group on Methods of Fish Stock Assessments • What does the other G stand for? • Has been renamed Methods Working Group • Met in Woods Hole 13-22 March 2007
Zeros Issue • Only addressed as a working paper • Similar to WP 3.1 from this meeting • Working Group did not spend much time on topic • ICES standard is to treat zeros as missing
Conclusions • Use a different error structure that allows zeros • Requires simulation testing for robustness to outliers • Delta approaches suggested but rejected • Quasi-likelihood function with quadratic term suggested (may be addressed in 2008) • One should not change data to fit the model, but rather change the model to fit the data