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At least 595 records · Page 33Linked to original sources
PubMed2000

Assessing joint pain complaints and locomotor disability in the Rotterdam study: effect of population selection and assessment mode.

OBJECTIVE: To assess the prevalence of self-assessed and physician-assessed disability and joint pain, their association, and the effect of cohort reduction and mode of assessment. DESIGN: Cross-sectional population survey. SETTING: General population, age 55 years and older. SUBJECTS: Independently living participants of the Rotterdam Study, including 1,156 men and 1,739 women. OUTCOME MEASURES: Self-reported and physician-assessed joint complaints. Patients' self-assessment of locomotor disability was by response to questions from the Stanford Health Assessment Questionnaire; physicians assessed patients' disability by administering activity tests. RESULTS: Reduction of the study cohort because of nonresponse and missing data had no influence on the frequency and effect measures. The physician-assessed prevalence of pain of the hips, knees, or feet was significantly lower than the self-assessed prevalence, with the percentage agreement being 83% for men and 74% for women, with kappa-values of approximately .40. The prevalence of physician-assessed locomotor disability was also significantly lower than the self-assessed disability, with the percentage agreement being 83% for men and 78% for women, with kappa values of .41 and .47, respectively. The associations of joint complaints with disability were similar for both modes of assessment. CONCLUSION: Cohort reduction caused by nonresponse and missing data had no influence on estimates of frequency and association. Self-assessment gives higher prevalences of joint complaints and locomotor disability than physician assessment, but the associations between complaints and disability were the same.

Aged↗
PubMedDate not supplied

A field-compatible method for interpolating biopotentials.

Mapping of bioelectric potentials over a given surface (e.g., the torso surface, the scalp) often requires interpolation of potentials into regions of missing data. Existing interpolation methods introduce significant errors when interpolating into large regions of high potential gradients, due mostly to their incompatibility with the properties of the three-dimensional (3D) potential field. In this paper, an interpolation method, inverse-forward (IF) interpolation, was developed to be consistent with Laplace's equation that governs the 3D field in the volume conductor bounded by the mapped surface. This method is evaluated in an experimental heart-torso preparation in the context of electrocardiographic body surface potential mapping. Results demonstrate that IF interpolation is able to recreate major potential features such as a potential minimum and high potential gradients within a large region of missing data. Other commonly used interpolation methods failed to reconstruct major potential features or preserve high potential gradients. An example of IF interpolation with patient data is provided to illustrate its applicability in the actual clinical setting. Application of IF interpolation in the context of noninvasive reconstruction of epicardial potentials (the "inverse problem") is also examined.

Action Potentials↗
PubMed2001

The Lancashire Quality of Life Profile: modification and psychometric evaluation.

BACKGROUND: Although widely used in Europe, the conceptual and psychometric qualities of the Lancashire Quality of Life Profile (LQoLP) have not been thoroughly examined. Four issues need attention: coverage, scale construction, systematic missing data, and psychometric properties. METHOD: Concept mapping was used to examine the coverage, and exploratory factor analysis to examine the empirical scale structure of the LQoLP. Data of 518 long-term patients from ten different mental health care settings were used. Modifications to the LQoLP were proposed on the basis of these findings, and its psychometric properties were tested. Thirty-one respondents participated in a test-retest reliability study (T1-T2: 2 weeks). RESULTS: The modified LQoLP covers the quality of life-concept in a more comprehensive manner. Internal consistency, test-retest reliability and validity are good. CONCLUSIONS: The modified version of the LQoLP now covers ten domains, paying specific attention to patients' definition of quality of life (autonomy, coping, self-worth). Domains are now based on factor analysis. The problem of systematic missing data is solved. Psychometric properties are good. Because of moderate alphas, two domains need further investigation.

Adult↗
PubMed2004

Quality of patient-reported outcome data captured using paper and interactive voice response diaries in an allergic rhinitis study: is electronic data capture really better?

BACKGROUND: Accuracy and reliability of diary data collected in allergic rhinitis trials depends on how and when the information is recorded by the subjects. OBJECTIVE: To compare diary data collected by using paper (optical mark readable) and electronic [telephone, interactive voice response system (IVRS)] tools. METHODS: There was a randomized, 3-week, 3-way, crossover trial, in 87 adults with allergic rhinitis recording diary data at home. Outcome measures were (1) comparison of symptom data during weeks when both or only 1 instrument was used; (2) missing data: and (3) ease of use and participant preference. RESULTS: More than 40,000 symptom data elements were recorded by 72 protocol-correct subjects. Symptoms recorded during the week that both instruments were used and when the 2 instruments were used alone were indistinguishable. Overall, 0.45% of paper and 4.12% of IVRS symptom data were missing. Of 10,080 paired data collected on paper and IVRS diaries during the week in which subjects used both, 94.44% were identical. Using IVRS, 63.2% of protocol-correct data were entered within the designated time and 87.6% within 1 half-day of the time specified; 85% of subjects preferred the paper instrument, 4% preferred IVRS, and 11% had no preference. CONCLUSIONS: A paper-based instrument can capture data indistinguishable from data captured from an electronic product. Processes to collect diary data should be evaluated for each study rather than simply to use the "latest" technology. Another interpretation is that frequency of recording diary data does not have a significant impact on outcomes.

Adult↗
PubMed1997

Data mining issues for improved birth outcomes.

Issues obstructing progress in data mining for improved health outcomes include data quality problems, data redundancy, data inconsistency, repeated measures, temporal (time-contextual) measures, and data volume. Related issues involve theoretical and technical problems involving uncertainty management, missing data and missing values, and matching appropriate data mining techniques to patient data sets. Results of data mining research in progress are reported for Duke University's perinatal database that contains nearly a decade of clinical patient data, 71,753 database (patient) records and 4-5000 variables per patient.

Artificial Intelligence↗
PubMed2005

Pramipexole and levodopa in early Parkinson's disease: dynamic changes in cost effectiveness.

BACKGROUND AND OBJECTIVE: In chronic disease, treatment effects and costs accumulate over time; hence, the choice of time horizon in cost-effectiveness analysis can be particularly important. In this article we analyse the dynamic changes in cumulative costs, effects and incremental cost effectiveness of two competing drug strategies in patients with early Parkinson's disease (PD). METHODS: Three hundred and one subjects with PD were randomised to initial pramipexole or levodopa and followed every 3 months over a 4-year period. Healthcare resource use was recorded in patient diaries and valued using a variety of sources at year 2002 US dollar values. Health-related quality of life (HRQoL) was measured using the EuroQoL EQ-5D. The study was conducted from a US societal perspective. Missing data were imputed using a multivariate fixed-effects model. Additional quality adjusted life years (QALY) gained by using pramipexole compared with levodopa were estimated as the area between the normalised treatment HRQoL profiles. The QALYs and costs for each treatment arm were calculated for various study horizons.The incremental cost-effectiveness ratio (ICER) and the net monetary benefit (NB) [using 50,000 US dollars, 100,000 US dollars and 150,000 US dollars as the value of a QALY] were estimated, and were bootstrapped to calculate the standard errors. Cost-effectiveness acceptability curves (CEAC) were built to estimate the probability that pramipexole was cost effective given different societal values of QALY, for various study horizons.We conducted sensitivity analyses on the ICER and the NB to test their robustness to various assumptions about missing data, for various subpopulations and under changes in the drug prices. RESULTS: Under the base-case assumptions, the ICER for pramipexole was 42,989 US dollars per QALY. Using the CEAC approach, the probability that pramipexole was cost effective relative to levodopa over the first 4 years was 0.57, 0.77 and 0.82 when a QALY was valued at 50,000 US dollars, 100,000 US dollars, and 150,000 US dollars, respectively. Over time, the ICER for pramipexole improved and uncertainty around the ICER decreased. If, after treatment withdrawal, HRQoL improved in pramipexole subjects and declined in levodopa subjects (best-case scenario for pramipexole), the probability of pramipexole being cost effective increased to 0.88, 0.96 and 0.98, respectively. Factors that improved the ICER of pramipexole were a decrease in the relative price of pramipexole and having low HRQoL or depression at baseline. CONCLUSIONS: The cost effectiveness of pramipexole compared with levodopa in the treatment of early PD increased as the time horizon of the clinical trial extended from 2 to 4 years. Our results suggest that pramipexole is more cost effective for patients with depression and low baseline HRQoL than in other patient subgroups.

Administration, Oral↗
PubMed2004

Development and testing of the health care system distrust scale.

BACKGROUND: Distrust of the health care system may be a significant barrier to seeking medical care, adhering to preventive health care and treatment regimens, and participating in medical research. OBJECTIVE: To describe the development and psychometric testing of an instrument (the Health Care System Distrust Scale) to measure distrust of the health care system. METHODS: Scale development involved 2 phases. In Phase 1, a pilot instrument was developed based on a conceptual model of health care-related distrust. Draft items were created using focus group sessions with members of the general public, literature review, and expert opinion. Draft items were pilot tested with 55 individuals waiting to be assigned to jury duty at the Municipal Court of Philadelphia. A priori, candidate items for elimination or revision included those with >5% missing data, extremely low or high interitem or item-total correlations, or those having a negative effect on the scale's internal consistency. In Phase 2, we conducted a survey of 400 prospective jurors to assess the reliability and validity of the final scale scores. RESULTS: In Phase 1, a 10-item scale was constructed that included 4 items measuring honesty, 2 items measuring confidentiality, 2 items measuring competence, and 2 items measuring fidelity. The participants in Phase 2 had a mean age of 41 years. Forty-three percent were African-American, 45% white, and 4% Hispanic. Scores on the Health Care System Distrust scale ranged from 12 to 46 with a possible range from 10 to 50. The mean score was 29.4 with a standard deviation of 6.33. No item had over 5% missing data. Internal consistency (Cronbach's alpha) was 0.75. Item-total correlations ranged from 0.27 to 0.57. Principal components analysis revealed 1 general component accounting for 32% of the variance. Nine of the variables had loadings higher than 0.40. As predicted, distrust of the health care system was higher among African Americans than whites and was inversely correlated with trust in personal physicians. CONCLUSIONS: Initial testing suggests that we developed an instrument with valid and reliable scores in order to measure distrust of the health care system. Future research is needed to evaluate the validity and reliability of the Health Care System Distrust scale among diverse populations. This instrument can facilitate the investigation of the prevalence, causes, and effects of health care system distrust in the United States.

Adult↗
PubMed2006

Choosing the analysis population in non-inferiority studies: per protocol or intent-to-treat.

For superiority trials, the intent-to-treat population (ITT) is considered the primary analysis population because it tends to avoid the over-optimistic estimates of efficacy that results from a per-protocol (PP) population. However, the roles of the ITT population and PP population in non-inferiority studies are not clearly defined as in superiority trials. In this paper, a simulation study is conducted to systematically investigate the impact of different types of missingness and protocol violations on the conservatism or anticonservatism of analyses based on the ITT and the PP population in non-inferiority trials. We find that conservatism or anticonservatism of the PP or ITT analysis depends on many factors, including the type of protocol deviation and missingness, the treatment trajectory (for longitudinal study) and the method of handling missing data in ITT population. The requirement that non-inferiority be shown for both PP and ITT populations does not necessarily guarantee the validity of a non-inferiority conclusion and a sufficiently powered PP analysis is not necessarily powered for ITT analysis. It is important to assess the potential types and rates of protocol deviation and missingness that might occur in a non-inferiority trial and to obtain some prior knowledge regarding the treatment trajectory of the test treatment versus the active control at the design stage so that a proper analysis plan and appropriate power estimation can be carried out. In general, for the types of protocol violations and missingness considered, we find that hybrid ITT/PP analysis, which excludes non-compliant patients as in the PP analysis and properly addresses the impact of non-trivial missing data as in the MLE-based ITT analysis, is more promising by way of providing reliable non-inferiority tests.

Analysis of Variance↗
PubMed2004

HAPLORE: a program for haplotype reconstruction in general pedigrees without recombination.

MOTIVATION: Haplotype reconstruction is an essential step in genetic linkage and association studies. Although many methods have been developed to estimate haplotype frequencies and reconstruct haplotypes for a sample of unrelated individuals, haplotype reconstruction in large pedigrees with a large number of genetic markers remains a challenging problem. METHODS: We have developed an efficient computer program, HAPLORE (HAPLOtype REconstruction), to identify all haplotype sets that are compatible with the observed genotypes in a pedigree for tightly linked genetic markers. HAPLORE consists of three steps that can serve different needs in applications. In the first step, a set of logic rules is used to reduce the number of compatible haplotypes of each individual in the pedigree as much as possible. After this step, the haplotypes of all individuals in the pedigree can be completely or partially determined. These logic rules are applicable to completely linked markers and they can be used to impute missing data and check genotyping errors. In the second step, a haplotype-elimination algorithm similar to the genotype-elimination algorithms used in linkage analysis is applied to delete incompatible haplotypes derived from the first step. All superfluous haplotypes of the pedigree members will be excluded after this step. In the third step, the expectation-maximization (EM) algorithm combined with the partition and ligation technique is used to estimate haplotype frequencies based on the inferred haplotype configurations through the first two steps. Only compatible haplotype configurations with haplotypes having frequencies greater than a threshold are retained. RESULTS: We test the effectiveness and the efficiency of HAPLORE using both simulated and real datasets. Our results show that, the rule-based algorithm is very efficient for completely genotyped pedigree. In this case, almost all of the families have one unique haplotype configuration. In the presence of missing data, the number of compatible haplotypes can be substantially reduced by HAPLORE, and the program will provide all possible haplotype configurations of a pedigree under different circumstances, if such multiple configurations exist. These inferred haplotype configurations, as well as the haplotype frequencies estimated by the EM algorithm, can be used in genetic linkage and association studies. AVAILABILITY: The program can be downloaded from http://bioinformatics.med.yale.edu.

Algorithms↗
PubMed2005

A metaanalysis of treatment outcomes of early enteral versus early parenteral nutrition in hospitalized patients.

OBJECTIVE: Nutritional support as enteral or parenteral nutrition (PN) is used in hospitalized patients to reduce catabolism. This study compares outcomes of early enteral nutrition (EN) with early PN in hospitalized patients. DESIGN: The authors conducted a metaanalysis of randomized, controlled trials (RCT) comparing early EN with PN. Studies on immunonutrition were excluded. Studies were categorized as medical, surgical, or trauma. PATIENTS: RCTs of early EN/PN were identified by search of 1) MEDLINE (1966-2002), 2) published abstracts from scientific meetings, and 3) bibliographies of relevant articles. MEASUREMENTS AND MAIN RESULTS: Thirty RCTs (ten medical, 11 surgical, and nine trauma) compared early EN with PN. The effect of nutrition type on hospital mortality and complication rates was reported as risk difference (RD%) and hospital length of stay (LOS) as mean weighted difference (MWD days). Missing data, by outcomes, varied from 20% to 63%. As a result of heterogeneity of treatment effects, the DerSimonian-Laird random-effects estimator was reported. There was no differential treatment effect of nutrition type on hospital mortality for all patients (0.6%, p = .4) and subgroups. PN was associated with increases in infective complications (7.9%, p = .001), catheter-related blood stream infections (3.5%, p = .003), noninfective complications (4.9%, p = .04), and hospital LOS (1.2 days, p = .004). There was no effect of nutrition type on technical complications (4.1%, p = .2). EN was associated with a significant increase in diarrheal episodes (8.7%, p = .001). Publication bias was not demonstrated. Metaanalytic regression analysis did not demonstrate any effect of age, time to initiate treatment, and average albumin on mortality estimates. Cumulative metaanalysis showed no change in the mortality estimates with time. CONCLUSION: There was no mortality effect with the type of nutritional supplementation. Although early EN significantly reduced complication rates, this needs to be interpreted in the light of missing data and heterogeneity. The enthusiasm that early EN, as compared with early PN, would reduce mortality appears misplaced.

Critical Care↗
PubMed1989

[Study on distribution form of mesiodistal crown diameter in large sample: Part II].

The purpose of this research was to examine the distribution of the tooth size in a large sample. The objective teeth were the left upper and lower fourteen teeth except the third molar. The tooth size of 1,000 dental casts from the Japanese female orthodontic patients was measured. On each of them, a histogram and a set of statistics (mean, standard deviation, coefficient of variation, skewness, kurtosis, Geary value) are given in order to examine the distribution. The findings are as follows: 1) Each tooth may be classified into the following four types of distribution except the congenitally missing data. TYPE I: A normal distribution was observed in the upper and lower central incisors, the lower lateral incisor, the lower canine, the upper and lower first premolars, the upper second premolar, the upper and lower first molars and the lower second molar. TYPE II: A positively skewed distribution was observed in the lower second premolar. TYPE III: A negatively skewed and leptokurtic distribution was observed in the upper canine and the upper second molar. TYPE IV: An extremely negatively skewed and leptokurtic distribution was observed in upper lateral incisor. 2) With the four teeth which were classified into TYPE II, TYPE III and TYPE IV, the distribution of the lower second premolar was concluded to be of normal distribution by logarithmic transformation. The distribution of the upper canine and the upper second molar was judged to be of lognormal distribution and the upper lateral incisor also was judged to be of three parameter lognormal distribution and four parameter lognormal distribution. 3) The distribution of thirteen teeth except the upper lateral incisor was judged to be of normal distribution, by considering the congenitally missing data and the outlier in statistical data of the tooth.

Asian People↗
PubMed2007

Gaussianization-based quasi-imputation and expansion strategies for incomplete correlated binary responses.

New quasi-imputation and expansion strategies for correlated binary responses are proposed by borrowing ideas from random number generation. The core idea is to convert correlated binary outcomes to multivariate normal outcomes in a sensible way so that re-conversion to the binary scale, after performing multiple imputation, yields the original specified marginal expectations and correlations. This conversion process ensures that the correlations are transformed reasonably which in turn allows us to take advantage of well-developed imputation techniques for Gaussian outcomes. We use the phrase 'quasi' because the original observations are not guaranteed to be preserved. We argue that if the inferential goals are well-defined, it is not necessary to strictly adhere to the established definition of multiple imputation. Our expansion scheme employs a similar strategy where imputation is used as an intermediate step. It leads to proportionally inflated observed patterns, forcing the data set to a complete rectangular format. The plausibility of the proposed methodology is examined by applying it to a wide range of simulated data sets that reflect alternative assumptions on complete data populations and missing-data mechanisms. We also present an application using a data set from obesity research. We conclude that the proposed method is a promising tool for handling incomplete longitudinal or clustered binary outcomes under ignorable non-response mechanisms.

Adolescent↗
PubMed1992

Pre-natal blood lead levels and learning difficulties in children: an analysis of non-randomly missing categorical data.

This paper presents an analysis of categorical variables subject to non-response. We incorporate the incomplete data into the analysis by modelling the distribution of the variables of interest and the non-response mechanism. We discuss issues of model selection and interpretation and the effect of discarding incomplete observations. In addition, we describe how to perform all of the computations with standard statistical software. We discuss the problem of incomplete categorical data within the context of a study of the effect of lead exposure on learning difficulties in children. In this study, many of the children are not observed on some of the variables of interest. It is particularly important in this study to incorporate the incomplete data, since there is evidence that non-response is related to the variables of interest. We reach different conclusions when we incorporate the incomplete data into the analysis than we reach when we discard the incomplete data. We also examine the sensitivity of our conclusions to the choice of a model for the non-response mechanism.

Algorithms↗
PubMedDate not supplied

A method for the analysis of repeated binary outcomes in randomized clinical trials with non-compliance.

When analysing repeated binary data from randomized trials, the model-based approaches, such as generalized estimating equations, are frequently used. Such methods ignore compliance information and give the model-based intention-to-treat estimate of treatment effect. In this paper, the design-based (randomization-based) semi-parametric estimation procedure is given in the estimation of causal risk difference. The resulting risk difference estimator is interpreted as an extension of the instrumental variables estimator for a binary outcome which has the causal interpretation. Extension of the proposed method to stratified analysis is given for data from stratified randomization or meta-analysis. It yields a Mantel-Haenszel type risk difference estimator. As a special case of stratified analysis, the pattern mixture model which stratifies the data by pattern of missing data is performed. Application of the proposed method to a trial in which endpoints were the occurrences of fever over three courses is provided. The same ideas are applied to the causal risk ratio estimation.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2005

Mixed-effects variance components models for biometric family analyses.

Recent substantive research on biometric analyses of twin and family data has used both a biometric path analysis model (PAM) and a biometric variance components model (VCM). Methodological research on these same topics have suggested benefits of using linear structural equation model algorithms (SEMA) as well as mixed effect multilevel algorithms (MEMA). To better understand the potential similarities and differences among these approaches we first highlight the algebraic equivalence between the standard biometric PAM and the corresponding biometric VCM models for family data. Second, we demonstrate how several SEMA programs based on either the PAM or VCM approach produce equivalent estimates for all phenotypic and biometric parameters. Third, we show how the biometric VCM approach (but not the PAM approach) can be easily programmed using current MEMA programs (e.g., SAS PROC MIXED). We then expand the scope of these different approaches to include measured covariates, observed variable interactions and multiple relatives within each family. MEMA software is compared to SEMA software for programming complex models, including the flexibility of data input, treatment of missing data, inclusion of covariates, and ease of accommodating varying numbers of observations (per family or individual).

Algorithms↗
PubMed1986

Correcting single channel data for missed events.

Interpretation of currents recorded from single ion channels in cellular membranes or lipid bilayers is complicated by the necessarily limited time resolution of the recording and detection systems. All intervals less than a certain duration, depending on the frequency response of the system, are not detected. Such missed events produce increases in the durations of observed open and shut intervals. In order to obtain the true kinetic scheme and rate constants underlying the observed activity, it is necessary to take into account missed events. We develop methods to correct for missed events for models with two or more states, including models with multiple open and shut states, compound states, and loops. Our methods can be used in a forward direction to predict observed distributions of open and shut intervals for a given kinetic scheme and time resolution. They can also be used in a backwards direction with iterative methods to determine rate constants consistent with the observed distributions. While a given kinetic scheme with rate constants predicts unique observed distributions of open and shut intervals, rate constants determined from observed distributions are not necessarily unique. Using these correction methods, we examine the effects of missed events for a five-state model consistent with some properties of large conductance Ca-activated K channels.

Ion Channels↗
PubMed2002

Comparison of commonly used orthopaedic outcome measures using palm-top computers and paper surveys.

INTRODUCTION: Measuring patient-perceived outcomes following orthopaedic procedures have become an important component of clinical research and patient care. General and disease-specific outcomes measures have been developed and applied in orthopaedics to assess the patients' perceived health status. Unfortunately, paper-based, self-administered instruments remain inefficient for collecting data because of: (a) missing data (b) respondent error, and (c) the costs to administer and enter data. OBJECTIVE: To study the comparability of palm-top computer devices and paper-pencil self-administered questionnaires in the collection of health-related quality of life (HRQL) information from patients. METHODS: The comparability of administering HRQL questionnaires using palm-top computer and traditional paper-based forms was tested in a sample of 96 patients with complaints of hip and/or knee pain. Each patient completed mailed versions of the Medical Outcomes Study (MOS), 36-item Health Survey (SF-36), and Western Ontario and McMasters University Arthritis Index (WOMAC) three weeks prior to presenting to clinic. At the clinic they were asked to complete the same outcomes measures using the palm-top computer or a paper-and-pencil version. ANALYSIS: In the analysis, scale distributions, floor and ceiling effects, internal consistency and retest reliability of scales were compared across the two data collection methods. Because the baseline characteristics of the groups were not strictly comparable according to age, the data were analyzed for the entire sample and stratified according to age. RESULTS: Few statistically significant differences were found for the means, variances and intra-class correlation coefficients between the methods of administration. While the scale distribution between the two methods was comparable, the internal consistency of the scales was dissimilar. CONCLUSIONS: Administration of HRQL questionnaires using portable palm-top computer devices has the potential advantage of decreased cost and convenience. These data lend some support for the comparability of palm-top computers and paper surveys for outcomes measures widely used in the field of orthopaedic surgery. The present study identified the lack of reliability across modes of administration that requires further study in a randomized comparability trial. These mode effects are important for orthopaedic surgeons to appreciate before implementing innovative data-capture technologies in their practices.

Aged↗
PubMed2003

Can the National Health and Nutrition Examination Survey III (NHANES III) data help resolve the controversy over low blood lead levels and neuropsychological development in children?

The National Health and Nutrition Examination Survey III (NHANES III) was designed to provide national estimates of the health and nutritional status of the United States population aged 2 months and above. A Youth data subset includes individuals from ages 2 months to 16 years totaling 13,944 individuals. Lanphear, Dietrich, Auinger, and Cox [U.S. Department of Health and Human Services, Public Health Reports, Public Health Report 2000, Vol. 115, p. 521] examined these data and concluded that deficits in cognitive and academic skills associated with lead exposure occur at blood lead concentrations of less than 5microg/dl. Attempts to replicate and extend these findings reveal serious shortcomings in the NHANES III data that center around missing data, odd distributions of blood lead levels as well as cognitive and academic scores, and potential inaccuracies in the data collection itself. A review of these issues is presented along with a series of empirical analyses of the data under multiple sets of assumptions leading to the conclusion that the NHANES III data are inherently inadequate for use in addressing neurodevelopmental issues. Policy issues and scientific issues related to cognitive and other neurodevelopmental phenomena should not be considered on the basis of the NHANES III Youth dataset.

Adolescent↗