title: Quantile regression in environmental health: Early life lead exposure and end-of-grade exams.
abstract: Conditional means regression, including ordinary least squares (OLS), provides an incomplete picture of exposure-response relationships particularly if the primary interest resides in the tail ends of the distribution of the outcome. Quantile regression (QR) offers an alternative methodological approach in which the influence of independent covariates on the outcome can be specified at any location along the distribution of the outcome. We implemented QR to examine heterogeneity in the influence of early childhood lead exposure on reading and math standardized fourth grade tests. In children from two urban school districts (n=1,076), lead exposure was associated with an 18.00 point decrease (95% CI: -48.72, -3.32) at the 10th quantile of reading scores, and a 7.50 point decrease (95% CI: -15.58, 2.07) at the 90th quantile. Wald tests indicated significant heterogeneity of the coefficients across the distribution of quantiles. Math scores did not show heterogeneity of coefficients, but there was a significant difference in the lead effect at the 10th (β=-17.00, 95% CI: -32.13, -3.27) versus 90th (β=-4.50, 95% CI: -10.55, 4.50) quantiles. Our results indicate that lead exposure has a greater effect for children in the lower tail of exam scores, a result that is masked by conditional means approaches.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, 1681 Campus Delivery, Fort Collins, CO 80523-1681, United States. Electronic address: sheryl.magzamen@colostate.edu.
authors.forename: Sheryl
authors.initials: S
authors.lastname: Magzamen
authors.affiliation: Department of Psychology, University of Wisconsin, 1202 West Johnson Street, Madison, WI 53706, United States.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Amato
authors.affiliation: Bureau of Environmental and Occupational Health, Wisconsin Department of Health Services, 1 West Wilson Street, Madison, WI 53703, United States.
authors.forename: Pamela
authors.initials: P
authors.lastname: Imm
authors.affiliation: Department of Surgery, University of Wisconsin, 600 Highland Ave, Madison, WI 53792, United States.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Havlena
authors.affiliation: Bureau of Environmental and Occupational Health, Wisconsin Department of Health Services, 1 West Wilson Street, Madison, WI 53703, United States.
authors.forename: Marjorie J
authors.initials: MJ
authors.lastname: Coons
authors.affiliation: Bureau of Environmental and Occupational Health, Wisconsin Department of Health Services, 1 West Wilson Street, Madison, WI 53703, United States.
authors.forename: Henry A
authors.initials: HA
authors.lastname: Anderson
authors.affiliation: Department of Population Health Sciences, University of Wisconsin, 707 WARF, 610 Walnut Street, Madison, WI 53726, United States; Nelson Institute for Environmental Studies, University of Wisconsin, 550 North Park Street, 122 Science Hall, Madison, WI 53706, United States.
authors.forename: Marty S
authors.initials: MS
authors.lastname: Kanarek
authors.affiliation: Department of Psychology, University of Wisconsin, 1202 West Johnson Street, Madison, WI 53706, United States; Department of Psychology, Montana State University, PO Box 173440, Bozeman, MT 59717, United States.
authors.forename: Colleen F
authors.initials: CF
authors.lastname: Moore
mesh_terms: D002648:Child; D004521:Educational Measurement / Q000706:statistics & numerical data; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D054624:Health Status Disparities; D006306:Health Surveys; D006801:Humans; D007854:Lead / Q000097:blood*; D007855:Lead Poisoning / Q000097:blood* / Q000453:epidemiology*; D008297:Male; D012044:Regression Analysis; D012574:Schools; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D014505:Urban Population; D014922:Wisconsin / Q000453:epidemiology
chemical_list: D007854:Lead
keywords: Education; Lead exposure; Pediatrics; Quantile regression; Socioeconomic status; Urban health