Environmental Conservation



A review of methods for the assessment of prediction errors in conservation presence/absence models


Alan H.  FIELDING a1c1 and JOHN F.  BELL a2
a1 Department of Biological Sciences, the Manchester Metropolitan University, Manchester M1 5GD, UK
a2 University of Cambridge Local Examinations Syndicate, University of Cambridge, Cambridge, UK

Abstract

Predicting the distribution of endangered species from habitat data is frequently perceived to be a useful technique. Models that predict the presence or absence of a species are normally judged by the number of prediction errors. These may be of two types: false positives and false negatives. Many of the prediction errors can be traced to ecological processes such as unsaturated habitat and species interactions. Consequently, if prediction errors are not placed in an ecological context the results of the model may be misleading. The simplest, and most widely used, measure of prediction accuracy is the number of correctly classified cases. There are other measures of prediction success that may be more appropriate. Strategies for assessing the causes and costs of these errors are discussed. A range of techniques for measuring error in presence/absence models, including some that are seldom used by ecologists (e.g. ROC plots and cost matrices), are described. A new approach to estimating prediction error, which is based on the spatial characteristics of the errors, is proposed. Thirteen recommendations are made to enable the objective selection of an error assessment technique for ecological presence/absence models.

(Received December 18 1996)
(Accepted March 1 1997)


Key Words: habitat relationships; data partitioning; habitat-association; model; classifier; threshold; validation.

Correspondence:
c1 Correspondence: Dr Alan Fielding. Tel: 144 161 247 1198. Fax: 144 161 247 6325. Email: A.Fielding@mmu.ac.uk