The selection of suitable indices for the measurement and analysis of fish condition

TLDR

A survey of fisheries journal studies shows that condition measurement using length‑weight data employs a wide variety of indices and statistical procedures, which can be grouped into individual‑fish condition factors and subpopulation regressions of log10 weight on log10 length. The authors reviewed the indices for appropriateness, simplicity, and statistical correctness. The study found that the observed condition patterns depend on both the index form and data set size, and that careful examination of index assumptions and data properties is essential for selecting an appropriate index.

Abstract

A survey of the studies published in two leading fisheries journals revealed that the analysis and measurement of condition, based on length‐weight data, has been performed using a wide variety of indices and statistical procedures. Eight forms of index were identified which can be categorized into those which measure the condition of individual fish, i.e. condition factors‘, and those which measure the condition of subpopulations as a whole, i.e. regressions of log, 10 weight on log, 10 length and the parameters of such regressions. Analysis of a test data set indicated that both the form of index and properties of the data set size can dictate the patterns of condition observed. The various indices were reviewed in terms of appropriateness, simplicity and statistical correctness. It was concluded that an index should be selected only after a detailed examination of both the underlying assumptions of the index and the properties of the data set.