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Open Access Research

Relevance of the type III error in epidemiological maps

Harald Heinzl1 and Thomas Waldhoer2*

Author Affiliations

1 Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University of Vienna, Vienna, Austria

2 Department of Epidemiology, Center for Public Health, Medical University of Vienna, Borschkegasse 8a, A-1090, Vienna, Austria

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International Journal of Health Geographics 2012, 11:34  doi:10.1186/1476-072X-11-34

Published: 18 August 2012

Abstract

Background

A type III error arises from a two-sided test, when one side is erroneously favoured although the true effect actually resides on the other side. The relevance of this grave error in decision-making is studied for epidemiological maps.

Results

Theoretical considerations confirm that a type III error may be large for regions with small numbers of expected cases even when no spatial smoothing has been performed. A simulation study based on infant mortality data in Austria reveals that spatial smoothing may additionally increase the risk of type III errors.

Conclusions

The occurrence of a type III error should be taken into account when interpreting results presented in epidemiological maps, particularly with regard to sparsely populated regions and spatial smoothing.

Keywords:
Directional test decision; Statistical power; Infant mortality; Standardised mortality ratio (SMR); Crude SMR estimator; Unstructured random effect; Structured random effect; BYM model