Impact of Cliff and Ord (1969, 1981) on Spatial Epidemiology

As defined by Elliott and Wartenberg (2004), spatial epidemiology is the description and analysis of geographic variations in disease with respect to demographic, environmental, behavioral, socioeconomic, genetic, and infectious risk factors. Spatial analyses abound in the epidemiological literature, with an early example found in the monograph edited by Doll (1984) on the geography of disease, in which large scale geographical variations of mortality for a number of chronic diseases were used to formulate hypotheses on the potential influence of life-style and environment. The paper on testing spatial autocorrelation by Cliff and Ord (1969) was highly instrumental in encouraging going beyond the simple display of disease maps and environmental atlases. It gave impetus to the development of a more formal statistical analysis framework, aimed at finely characterising the scale of spatial dependence and the type of geographical patterns, whether in the disease rates themselves or in the residuals of geographical correlation studies. Recent books on Spatial Epidemiology by Elliott et al (2000), Lawson (2006, 2008) and Pfeiffer et al (2008) all discuss the central concept of autocorrelation formalised in Cliff and Ord (1969) in order to lay the foundations for more sophisticated analyses. They also describe a series of recent examples, which show how the field has moved on from large scale descriptive studies towards more powerful small area studies that take advantage of the advances in geographical information systems.