| Testing the Dose-Response Specification in Epidemiology: Public Health and Policy Consequences for Lead Stephen J. Rothenberg1 and Jesse C. Rothenberg2 1National Institute of Public Health, Center for Research in Population Health, Cuernavaca, Morelos, Mexico; 2University of Sydney, Faculty of Economics and Business, School of Economics and Political Science, Camperdown, New South Wales, Australia Abstract
Statistical evaluation of the dose-response function in lead epidemiology is rarely attempted. Economic evaluation of health benefits of lead reduction usually assumes a linear dose-response function, regardless of the outcome measure used. We reanalyzed a previously published study, an international pooled data set combining data from seven prospective lead studies examining contemporaneous blood lead effect on IQ (intelligence quotient) of 7-year-old children (n = 1,333) . We constructed alternative linear multiple regression models with linear blood lead terms (linear-linear dose response) and natural-log-transformed blood lead terms (log-linear dose response) . We tested the two lead specifications for nonlinearity in the models, compared the two lead specifications for significantly better fit to the data, and examined the effects of possible residual confounding on the functional form of the dose-response relationship. We found that a log-linear lead-IQ relationship was a significantly better fit than was a linear-linear relationship for IQ (p = 0.009) , with little evidence of residual confounding of included model variables. We substituted the log-linear lead-IQ effect in a previously published health benefits model and found that the economic savings due to U.S. population lead decrease between 1976 and 1999 (from 17.1 µg/dL to 2.0 µg/dL) was 2.2 times ($319 billion) that calculated using a linear-linear dose-response function ($149 billion) . The Centers for Disease Control and Prevention action limit of 10 µg/dL for children fails to protect against most damage and economic cost attributable to lead exposure. Key words: child IQ, dose response, health benefit, health policy, lead. Environ Health Perspect 113:1190-1195 (2005) . doi:10.1289/ehp.7691 available via http://dx.doi.org/ [Online 10 May 2005]
Address correspondence to S.J. Rothenberg, Center for Research in Population Health, National Institute of Public Health, Avenida Universidad 655, Sta. María Ahuacatitlán, CP 62508 Cuernavaca, Morelos, México. Telephone/Fax: 52-739-395-0662. E-mail: drlead@prodigy.net.mx We thank the pooled data study authors for permission to use the data. We especially thank R. Canfield, who reviewed early versions of the manuscript and suggested residual confounding issues and health benefit models. This work was supported in part by the Secretariat of Health, Mexico ; Consejo Nacional de Ciencia y Tecnología (CONACyT) grant SALUD-2002-C01-7159 ; and the U.S. Environmental Protection Agency. The authors declare they have no competing financial interests. Received 22 October 2004 ; accepted 10 May 2005.
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