in girls (Pastor and Reuben 2008; Staller and Faraone 2006). The aim of this paper is to investigate associations between in utero and childhood OP pesticide exposure as assessed by uri- nary DAP metabolites and attention-related outcomes in 3.5- and 5-year-old Mexican- American children living in an agricultural community in California. We include assess- ment of attentional problems based not only on maternal report, as in previous studies, but also by direct neuropsychological testing and psychometrician observation. Materials and Methods Participants and recruitment. The Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) is a prospective birth cohort aimed at studying the association of pesticides and other envi- ronmental agents on the health of pregnant women and their children living in the Salinas Valley, California. Details for this study have been described previously (Eskenazi et al. 2004, 2007). Briefly, women in their first half of pregnancy were recruited between October 1999 and October 2000 from participating prenatal care clinics serving the farmworker community. Eligible women were ≥ 18 years of age, eligible for California’s low-income health insurance program, planning to deliver at the county medical center, and spoke Spanish or English. Women gave written informed consent to participate. The study was approved by the institutional review board at University of California, Berkeley. We followed 526 women to delivery of a liveborn, surviving singleton. We excluded from the present analyses children who did not have a prenatal DAP metabolite measure- ment (n = 2), who had a medical condition that could affect neurobehavioral assessment (n = 3; deafness, Down syndrome, hydro- cephalus), or who were lost to follow-up or did not participate at the 3.5- or 5-year study visit (n = 173). The final population included 348 children who had available data at 3.5 and/or 5 years of age. Total DAPs were meas- ured in maternal urine collected at two time points during pregnancy and in child urine collected at the 3.5-year and 5-year visits. Levels of DAPs were similar in mothers of children included in the present analysis rela- tive to those whose children were not (t-test p = 0.40). Distributions of other covariates measured before 3.5 years of age were also similar, except that more boys than girls had dropped from the study (χ2 p = 0.04). Maternal interviews and assessments. We interviewed mothers twice during pregnancy (mean gestation, 14.0 and 26.6 weeks), after delivery, and when children were 6 months and 1, 2, 3.5, and 5 years of age. Interviews were conducted by bilingual, bicultural interviewers in Spanish or English. Mothers were administered the Peabody Picture Vocabulary Test (PPVT) (Dunn and Dunn 1981; Dunn et al. 1986) at the 6-month visit to assess receptive vocabulary, which was used as an indicator of verbal intelligence, and the Center for Epidemiologic Studies Depression Scale (CES-D) (Radloff 1977) at the 3.5-year visit. A registered nurse abstracted prenatal and delivery medical records. Attention-related outcomes. We measured attention-related outcomes in three ways: maternal report of child behavior at 3.5 and 5 years of age; direct assessment of the child at 3.5 and 5 years; and psychometrician’s report of the behavior of the child during testing at 5 years. Mothers completed the Child Behavior Checklist (CBCL) for 1.5–5 years of age (Achenbach and Rescorla 2000) as part of the maternal interview at the 3.5- and 5-year visits to assess emotional/behavioral problems and competencies of the children. This 99-item scale, which is available in English and Spanish and has been widely used in cross-cultural research, collects data on a variety of behaviors that the parent rates as “not true,” “somewhat true,” or “very true/often true” currently or within the preceding 2 months. Questions are combined to create scores reflecting possible problem areas, including some correspond- ing to Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV) diagnoses (American Psychiatric Association 2000) and others reflecting problem syndrome areas. The present analyses focused on two related atten- tion scores: the attention problems scale and the DSM-related ADHD scale. Scores can be examined continuously or by the proportion above a standard cutoff score, for example, > 93rd percentile (borderline clinical range) or > 97th percentile (clinical range). Because few children fell into the clinical-range category for these scales (n = 3–11), we used the borderline clinical range cut-point as well as continuous raw scores in multivariate analyses. Children also completed a battery of neurodevelopmental tests at each visit. At the 3.5-year visit, the visual attention sub- test of the NEPSY-II (Korkman et al. 1997) was administered to children by trained psy- chometricians. Children were asked to cir- cle specific images on a page of pictures that included distracters. For data analysis, we used continuous scores scaled to a normative sample of U.S. children; the age-standardized mean ± SD for this subtest is 10 ± 3. During the 5-year neurodevelopmen- tal assessment, which took approximately 2 hr to complete, trained psychometricians administered to children the Conners’ Kiddie Continuous Performance Test (K-CPT) (Conners and Staff 2001). The K-CPT is a 7-min computerized test that assesses reaction Environmental Health Perspectives • volume 118 | number 12 | December 2010 Organophosphate pesticides and attention time, accuracy, and impulse control. Briefly, children were instructed to press the space bar when they saw any image on the computer screen except a ball. The computer program yields T-scores age-standardized to a general U.S. population (mean ± SD = 50 ± 10) for errors of commission (i.e., the child responds when he or she should not), errors of omis- sion (i.e., the child fails to respond when he or she should), and hit reaction time. We examined T-scores continuously and cat- egorically using the cutoff of T-score > 65, which is considered markedly atypical. The program also combines measures to gener- ate a clinical ADHD Confidence Index score (range, 0–100). For statistical analyses, we use continuous Confidence Index percentiles and selected a cut-point of > 70th percentile (meaning that 70% of children performing similarly on the test could be correctly classi- fied as having clinical ADHD). Following the 5-year neurodevelopmen- tal assessment, psychometricians blinded to exposure status answered several subjective questions evaluating the behavior of the child during the 2-hr visit, including four questions derived from the seven-item Hillside Behavior Rating Scale (Gittelman and Klein 1985). We summed responses to two questions assessing motor activity and distractibility to create an adapted ADHD symptoms scale. The Hillside Scale is associated with parent and teacher rat- ings and has been found to add significantly to the clinical prediction of ADHD (Willcutt et al. 1999). We created a dichotomized Hillside outcome variable with scores ≥ 7 of 12 possible points (representing < 10% of children) to flag children displaying a higher degree of attention problems based on psy- chometricians’ observation. To identify children whose behaviors on multiple indices at 5 years of age were most suggestive of possible ADHD within our cohort, we created a composite ADHD vari- able that combined maternal report (CBCL), child testing (K-CPT), and psychometrician report (Hillside). Children were coded 1 for the ADHD indicator if they met at least two of the following conditions at 5 years of age: CBCL ADHD scale in borderline clinical range (maternal report); standardized K-CPT ADHD Confidence Index ≥ 60% (child test- ing); and Hillside ADHD scale in the upper quartile of values (psychometrician report). The CBCL was completed by 331 mothers at the 3.5-year interview and 323 mothers at the 5-year interview. NEPSY scores were avail- able for 320 3.5-year-olds, and K-CPT scores were available for 312 5-year-olds. Hillside scores were available for 322 5-year-olds. Pesticide exposure measurement. Details of urine collection, analysis, and quality control procedures, including detection limits and use of blanks and spikes, are described elsewhere 1769