Higher-than-expected rates of pediatric cancers have been identified in the Miami metro area and an area west of the Everglades in a series of five statistical analyses conducted for Science and Public Policy.
In a review of the analyses (2015; doi:10.1080/2330443X.2015.1026621), Lance A. Waller, PhD, a biostatistics professor specializing in spatial epidemiology at Emory University in Atlanta, Georgia, urged care in next steps. He recommended that state and local follow-up go “beyond a dichotomous ‘cluster found/not found’ outcome and to look carefully at where, when and how methods agree, as well as where, when, and how they differ … to aid the transition between statistical results, epidemiologic insight, and policy decisions.”
Five research teams detected the anomalous rates. Each team used different epidemiologic and statistical methodology, on a data set spanning the period 2000 to 2010 provided by Florida Association of Pediatric Tumor Programs (FAPTP). The FAPTP is a consortium of diagnosis and treatment centers that consolidates data for incorporation into the Florida Cancer Data System, part of the National Program of Cancer Registries of the US Centers for Disease Control and Prevention (CDC).
The research groups applied different analytical approaches to achieve the same goal: detect spatio-temporal pediatric cancer clusters. The analyses used familiar methods of scan statistics, classification, and hierarchical Bayesian modeling, as well as some ideas new to disease clustering: wombling and machine learning.
During their respective analyses of the FAPTP data, the research groups found several suggestive results. For instance, each approach identified local areas in which the observed pediatric cancer rate is statistically significantly higher than the rate expected given the number of people at risk. While the precise areas of high reported risk differ between methods, the groups identified a few common results that are not identical, but overlap.
All five teams identified statistically elevated rates of pediatric cancers in an urban area within collections of ZIP code tabulation areas (ZCTAs) in the Miami metro area and in an area just west of the Everglades. (ZCTAs are geographic areas defined by the US Census Bureau to provide a link between census geography—blocks, block groups, and tracts—and US Postal Service ZIP code areas.)
One analysis reveals the local increase west of the Everglades is based on two cases, both classified as “Other” race, while another analysis indicates this cluster is limited to the year 2000.
The observed elevated rates near Miami involve a much larger population size and many more cases, factors that complicate the identification of any shared characteristics common to cases in the cluster.
Subtle differences occurred between the specific clusters identified by the various analytical approaches. Comparisons across analyses reveal characteristics of the detected patterns, including the number of cases (two), types of cancer (leukemia or brain/central nervous system cancer), and the racial composition and timing of the cluster west of the Everglades.
The identified clusters are geographically quite large and therefore unlikely to provide clear links between particular environmental exposures to local risks, added Waller in his analysis.