Quantile regression in environmental health: Early life lead exposure and end-of-grade exams.

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 (ß=-17.00, 95% CI: -32.13, -3.27) versus 90th (ß=-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.

Moderate lead exposure and elementary school end-of-grade examination performance.

PURPOSE: This study investigated the association between moderate lead poisoning in early childhood with performance on a comprehensive set of end-of-grade examinations at the elementary school level in two urban school districts. METHODS: Children born between 1996 and 2000 who resided in Milwaukee or Racine, WI, with a record of a blood lead test before the age of 3 years were considered for the analysis. Children were defined as exposed (blood lead level ≥10 and <20 µg/dL) or not exposed (BLL < 5 µg/dL). Parents of eligible children were mailed surveys to consent to participation and elicit information on potential confounders. On consent, children were matched to educational records for fourth grade Wisconsin Knowledge and Concepts Examinations. Seemingly unrelated regression was used to evaluate the relation between scaled scores on all sections of the examination (math, reading, language arts, science, and social studies) with exposure status, controlling for demographics, social status indicators, health indicators, and district-based poverty indicators. RESULTS: A total of 1133 families responded to the survey and consented to have educational records released; 43% of children were considered exposed. After controlling for demographic and socioeconomic covariates, lead exposure was associated with significantly lower scores in all sections of the Wisconsin Knowledge and Concepts Examinations (range: science, ß = -5.21, P = .01; reading, ß = -8.91, P = .003). Children who were black, had a parent with less than a high-school education, and were classified by parents as having less than excellent health had significantly lower performance on all examination components. CONCLUSIONS: Children with moderate lead poisoning in early childhood performed significantly lower on all components of elementary school end-of-grade examinations compared with unexposed children. Household level social status and childhood health indicators partially explain decreased examination scores.

Lead exposure and educational proficiency: moderate lead exposure and educational proficiency on end-of-grade examinations.

PURPOSE: To investigate and quantify the impact of moderate lead exposure on students' ability to score at the "proficient" level on end-of-grade standardized tests. METHODS: We compared the scores of 3757 fourth grade students from Milwaukee, Wisconsin, on the Wisconsin Knowledge and Concepts Exam (WKCE). The sample consisted of children with a blood lead test before age 3 years that was either unquantifiable at the time of testing (<5 µg/dL) or in the range of moderate exposure (10-19 µg/dL). RESULTS: After controlling for gender, poverty, English language learner status, race/ethnicity, school disciplinary actions, and attendance percentage, results showed a significant negative effect of moderate lead exposure on academic achievement for all 5 subtests of the WKCE. Test score deficits owing to lead exposure were equal to 22% of the interval between student categorization at the "proficient" or "basic" levels in Reading, and 42% of the interval in Mathematics. CONCLUSIONS: Children exposed to amounts of lead before age 3 years that are insufficient to trigger intervention under current policies in many states are nonetheless at a considerable educational disadvantage compared with their unexposed peers 7 to 8 years later. Exposed students are at greater risk of scoring below the proficient level, an outcome with serious negative consequences for both the student and the school.

Mercy mercy me: social injustice and the prevention of environmental pollutant exposures among ethnic minority and poor children.

Children's lead and pesticide exposures are used as examples to examine social disparities in exposure reduction efforts as well as environmental policies impacting children in poverty and minority children. The review also presents an estimate of the effect of social disparities in lead exposure on standardized test performance. Because including measures of pollutants with potential behavioral effects can alter the observed effects of race/ethnicity, income, and other variables, suggestions are made for including measures of pollutants in longitudinal studies and studies of multiple and cumulative risk. Continued basic research on developmental correlates and effects of pollution exposure, participatory action-research with at-risk and underrepresented populations, and contributions to public awareness and education are important leadership areas for developmental researchers.

Laboratory assessment of temperament and environmental enrichment in rhesus monkey infants (Macaca mulatta).

This study investigated the combined effects of early temperamental characteristics and environmental enrichment on a variety of developmental measures in nursery-reared rhesus monkey infants. Twenty-three infants, reared in either standard laboratory cages or enriched environments, were tested during the 1st month of life for interactive, motor, and temperamental capabilities and characteristics. At 8 months of age, all subjects were assessed on a second series of tests designed to measure their problem-solving skills, motor capabilities, and temperamental responses under challenge. Results indicated that enrichment was associated with higher scores on subsequent problem-solving and motor tests. However, such effects were found to combine with early temperament ratings. Specifically, individuals performing best on the 8-month tests had not only been reared in enriched environments, but also had been rated low on fearfulness during the early assessment. In addition, individuals scoring poorest had been rated as fearful initially in addition to being reared without enrichment. Results indicated that while high ratings on early laboratory assessments of fearfulness may be predictive of poorer problem-solving performance under challenging conditions, these adverse effects may be partially attenuated by environmental enrichment.