Publication Abstract

Temporal trend monitoring: Robustmethod for analysisng contaminant trend monitoring data

M.D. Nicholson, R.J. Fryer and J.R. Larsen

This document describes a new method of assessing contaminant trends in fishmuscle, fish liver, and shellfish.

Previous methods of assessing trend datahave often been complicated by the need to respond to unusual features of the data, eitherin the way they were collected, processed, or in their distribution. These complicationsare discussed in detail to show the reasoning behind the method described here, which aimsto provide a simpler, robust and more complete method of analysing and presenting trends.

Essentially, the method summarizes trendsusing a smoother, a specific class of smooth curves fitted to median log-concentrations.The theory and methodology of fitting smoothers is new and our knowledge of theperformance of the fitted smoothers, particularly with small sample sizes, is onlyapproximate. Although a preliminary application of the new method to the 1993 assessmentof the data from the Joint Monitoring Programme of the Oslo and Paris Commissions waspromising, more assessment and development of the method will be necessary. A very simplesmoother is used here to make the computations and theory easy to follow.

A detailed worked example is provided.Statistical theory and formulae are included as annexes.

Reference:

M.D. Nicholson, R.J. Fryer and J.R. Larsen, 1998. Temporal trend monitoring: Robust methodfor analysisng contaminant trend monitoring data. ICES Techniques in Marine EnvironmentalSciences, 20: 22pp.