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WP 3.3 ICES WGMG Zeros

This working paper from the ICES Working Group on Methods of Fish Stock Assessments addresses the treatment of zeros in fish stock data. Meeting at Woods Hole from March 13-22, 2007, the group acknowledged zeros as missing data, advocating for an error structure that accommodates these values. Simulation testing was deemed necessary for robustness, while delta approaches were considered but ultimately rejected. A quasi-likelihood function with a quadratic term was proposed and may be explored further in 2008. The emphasis remains on adjusting models to fit data, not altering data to conform to models.

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WP 3.3 ICES WGMG Zeros

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  1. WP 3.3 ICES WGMG Zeros

  2. 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

  3. 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

  4. 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

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