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PubMed2003

Design strategies and innovations in the medical expenditure panel survey.

BACKGROUND: Recent efforts to provide an annual profile of the health care quality of the nation's health care delivery system and to identify health care disparities in the population's access to and use of health care services have served to stimulate design innovations and content enhancements to the Medical Expenditure Panel Survey (MEPS). OBJECTIVES: To present a summary of the analytical objectives, design, and core content of the MEPS, and to provide an overview of the new and innovative design features that add capacity for health status and quality of care measurement and improve data quality. SUMMARY: The MEPS questionnaire has been expanded to include content taken from the Consumer Assessment of Health Plans Study (CAHPS) to facilitate assessments of patient experiences with health care at the national level. The survey now includes the series of questions from the SF-12 and the EuroQol 5D to improve the survey's capacity to measure health status. Additional condition-specific questions for diabetes, asthma, high blood pressure, and heart disease were added to identify the health care services received for treatment and to determine whether the care received was consistent with practice guidelines. Sample design modifications are presented, with particular emphasis given to a summary of the recent sample size increase and resultant improvements in the precision of resultant survey estimates. Attention is also given to changes in survey design, estimation, and data collection strategies that improve data quality.

Bias↗

PubMed2004

Genetic and environmental contributions to the Child Behavior Checklist Obsessive-Compulsive Scale: a cross-cultural twin study.

CONTEXT: We have reported elsewhere on the development of an 8-item Obsessive-Compulsive Scale (OCS) contained in the Child Behavior Checklist (CBCL) to identify children who meet criteria for DSM-IV obsessive-compulsive disorder. Twin studies of obsessive-compulsive disorder have indicated a significant genetic component to its expression. OBJECTIVE: To determine the relative contributions of genetic and environmental influences on childhood obsessive-compulsive behavior using the CBCL OCS in twin samples. DESIGN: The CBCL data were received by survey of twins in the Netherlands Twin Registry (NTR) and the Missouri Twin Study (USA/MOTWIN). SETTING: General community twin samples. PARTICIPANTS: Participants were 4246 twin pairs aged 7 years, 2841 aged 10 years, and 1562 aged 12 years (who also participated in the study at 7 and 10 years of age) from the NTR and 1461 mixed-age twin pairs (average age, approximately 9 years) from the USA/MOTWIN. MAIN OUTCOME MEASURES: Model fitting to test for genetic and environmental influences, sex differences, and sibling interaction/rater contrast effects on the CBCL OCS. RESULTS: In each case, the best-fitting model was one that indicated significant additive genetic influences (range, 45%-58%; 95% confidence interval [CI], 45%-61%), and unique environmental influences (range, 42%-55%; 95% CI, 39%-55%), with shared environmental influences in the NTR sample aged 12 years (16%). Sex differences were seen in the mixed-age USA/MOTWIN model, but not in the NTR samples. No evidence of dominance, sibling interaction, or rater-contrast effects was seen. These data were relatively consistent across age and cultures. CONCLUSIONS: The CBCL OCS is influenced by genetic factors (approximately 55%) and unique environmental factors (approximately 45%) in the younger sample, with common environmental influences only at 12 years of age. These effects do not vary with differences in sex or sibling interaction/rater contrast effects. Our data reveal higher genetic influences for obsessive-compulsive behavior and do not demonstrate genetic differences across sex.

Age Factors↗

PubMed2006

Sampling scale effects in random fields and implications for environmental monitoring.

The concept of a sampling scale triplet of spacing, extent and support is used to define the spatial dimensions of a monitoring network or a field study. The spacing is the average distance between samples, the extent is the size of the domain sampled and the support is the averaging area of one sample. The aim of this paper is to examine what is the bias and the random error (uncertainty) introduced by the sampling scale triplet into estimates of the mean, the spatial variance and the integral scale of a variable in a landscape. The integral scale is a measure of the average distance over which a variable is correlated in space. A large number of two dimensional random fields are generated from which hypothetical samples, conforming to a certain sampling scale triplet, are drawn which in turn are used to estimate the sample mean, spatial variance and integral scale. The results indicate that the biases can be up to two orders of magnitude. The bias of the integral scale is positively related to the magnitude of any of the components of the scale triplet while the bias of the spatial variance is different for different components of the scale triplet. All sampling scale effects are relative to the underlying correlation length of the variable of interest which is closely related to the integral scale. The integral scale can hence be used for sampling design and data interpretation. Suggestions are given on how to adjust a monitoring network to the scales of the variables of interest and how to interpret sampling scale effects in environmental data.

Data Collection↗

PubMed1985

Effect of dose of bovine growth hormone on milk composition: alpha-lactalbumin, fatty acids, and mineral elements.

Tissue-specific effects of bovine growth hormone on lactating dairy cows were examined by analysis of milk composition. Milk samples were from 6 cows that received subcutaneous injections of 0, 5, 10, 25, 50, and 100 IU/d of growth hormone in a Latin-square design. Samples from the last 5 d of each 10-d treatment period were pooled for analyses of milk components. Concentration of alpha-lactalbumin in milk increased progressively across the treatment range up to 32% above controls (1.30 mg/nl) at the 100 IU dose. Specific alpha-lactalbumin synthesis (expressed as a percent of total milk protein) was also increased. Secretion of de novo synthesized fatty acids (short and medium chain length) in milk was increased, but response plateaued between the 50 and 100 IU/d. Secretion of preformed (long-chain) fatty acids progressively increased across the entire dose range. Thus, the percentage of long-chain fatty acids in milk increased at the highest doses of hormone. Changes in fatty acid composition of milk were apparently related to energy status; the milk response to 50 and 100 IU/d of growth hormone caused cows to be in or near negative energy balance. Exogenous growth hormone did not affect the concentration of calcium, phosphorus, sodium, iron, copper, and manganese in milk. Results are consistent with growth hormone functioning in homeorhesis to coordinate the partitioning of all nutrients to support the increased secretion of milk and milk components.

Animals↗

PubMed2005

A national profile of health care utilization and expenditures for children with special health care needs.

OBJECTIVES: To provide the first nationally representative data on total health care expenses, out-of-pocket health care expenses, and information on the extent to which out-of-pocket expenses are financially burdensome for families of children with special health care needs (CSHCN). To also compare utilization and expenditure patterns for children with and without special health care needs. DESIGN: We used data from the 2000 Medical Expenditure Panel Survey (MEPS). We present univariate, bivariate, and multivariate statistics on utilization and expenditures adjusted for the complex sample design. PARTICIPANTS: The 2000 MEPS data set contains 6965 children younger than 18 years. Using the CSHCN definition adopted by the federal Maternal and Child Health Bureau and operationalized using the CSHCN Screener, 949 children (15.6%) were identified as children with special health care needs. MAIN OUTCOME MEASURES: Compared with other children, CSHCN had 3 times higher health care expenditures (2099 dollars vs 628 dollars; P<.01). The 15.6% of CSHCN accounted for 42.1% of total medical care costs (excluding dental costs) and 33.6% of total health care costs (including dental costs) attributed to children in 2000. Families of CSHCN were best protected against inpatient hospital care expenses and most exposed to dental care expenses. Families of CSHCN experiencing high out-of-pocket expenses (exceeding 5% of family income) were approximately 11 times more likely to be from households with incomes below 200% of the federal poverty level (odds ratio, 10.9; 95% confidence interval, 3.55-33.76) than to be from families with incomes at or above 400% of the federal poverty level. CONCLUSIONS: Families with CSHCN experience much higher expenditures, including out-of-pocket expenditures, than other children. Insurance plays an important protective role for families of CSHCN, but it still provides incomplete protection. Health policy changes that would extend the breadth and depth of insurance coverage are needed to ensure that all families of CSHCN are protected against burdensome expenses.

Adolescent↗

PubMed2005

Barriers to HIV-testing among Hispanics in the United States: analysis of the National Health Interview Survey, 2000.

Data from the 2000 National Health Interview Survey (NHIS) were analyzed to explore barriers to HIV testing, and intentions to be tested among a nationally representative sample (n = 4,261) of the different Hispanic subgroups living in the United States. Weighted proportions and variances accounting for the complex sample design of the NHIS were estimated using the Taylor series linearization method. Regression estimates are expressed as odds ratios and their 95% confidence intervals. Two thirds of sampled Hispanics had never been tested for HIV (excluding blood donations) and 88% expressed no intention to do so in the near future. Many of the factors that influence the likelihood of having been tested in the past also impact on future HIV testing intentions including age, Hispanic subgroup, high-risk status, and self-perceived HIV risk. Compared to Puerto Ricans, Mexicans (odds ratio [OR] = 1.59, 1.1-2.3) and Mexican/Americans (OR = 1.61, 1.1-2.3) were more likely to never have been tested and Cubans were notably more likely to report negative future testing intentions (OR = 5.63, 2.5-12.8). Among Hispanics who reported high-risk status or high/medium self-perceived HIV risk, more than one quarter had never undergone testing and expressed no intention of doing so in the near future. Recognition of the HIV testing barriers identified in this study is valuable for the development and refinement of current strategies that aim to increase HIV testing practices in the heterogeneous U.S. Hispanic population.

AIDS Serodiagnosis↗

PubMed2007

Variation of estimates of SNP and haplotype diversity and linkage disequilibrium in samples from the same population due to experimental and evolutionary sample size.

Studies of genetic polymorphisms and diversity between and within human populations are increasingly characterised by a very large number of genetic markers but using a relatively small number of individuals from which DNA samples were taken. In this report we examine the limitations of a small experimental sample size relative to a large genomic sample size, and quantify the sampling variance of a number of measures of diversity and linkage disequilibrium. The relationship between sample size and observed levels of polymorphism and haplotype diversity at the level of a gene is investigated under a neutral model of sequence evolution, using coalescent simulations. It is shown that the effect of evolutionary sampling, as manifested by differences between samples (genes) in measures of diversity estimated using very large sample sizes, is substantial, with a coefficient of variation of the number of detected polymorphic SNPs or haplotypes in the order of 15%. The effect of experimental design (sample size) is also very large, and a number of 'significant' results reported in the literature can be explained by sampling alone. The expected correlation coefficient of measures of linkage disequilibrium across samples from the same population has been quantified and found to be consistent with empirical estimates from the literature.

Chromosomes, Human↗

PubMed1995

Nasometric discrimination of hypernasality and turbulent nasal airflow.

Agreement between nasalance measures and perception of nasality during speech is not consistently strong. A possible reason may be the complicating combined effects of nasal turbulent airflow and nasal resonance. The purpose of this preliminary study was to examine nasalance measures obtained during production of a low pressure speech sample designed to minimize or eliminate the effects of turbulent nasal airflow. The results showed that nasalance measures obtained as some of the subjects produced the new speech sample were significantly different from those obtained when the standard high pressure speech sample was used. Use of both the new low pressure samples and the standard high pressure samples may result in improved agreement between nasalance measures and ratings of speech nasality as well as assist in the identification of subgroups of patients with marginal velopharyngeal insufficiency.

Acoustics↗

PubMed2005

[Methods of the Mexican National Performance Assessment Survey].

OBJECTIVE: To describe the sampling design, operative strategy, and data management used in the Encuesta Nacional de Evaluaci6n del Desempeño (Mexican National Performance Assessment Survey). MATERIAL AND METHODS: A probabilistic, multistage, stratified sample was used to make inferences for each state of the country with representativeness of the urban and rural localities of Mexico. The survey was conducted between November 2002 and April 2003. The study population consisted of individuals in their households. RESULTS: Forty-thousand households were visited all over the country, and 38,746 interviews were obtained,with a non-response rate considerably lower than expected. CONCLUSIONS: The methods used to carry out the National Performance Assessment Survey allowed calculation of estimates with measurable accuracy in terms of error and confidence, making the results inferable to the national population.

Delivery of Health Care↗

PubMed1996

Variance estimation for complex surveys using replication techniques.

The analysis of survey data requires the application of special methods to deal appropriately with the effects of the sample design on the properties of estimators and test statistics. The class of replication techniques represents one approach to handling this problem. This paper discusses the use of these techniques for estimating sampling variances, and the use of such variance estimates in drawing inferences from survey data. The techniques of the jackknife, balanced repeated replication (balanced half-samples), and the bootstrap are described, and the properties of these methods are summarized. Several examples from the literature of the use of replication in analysing large complex surveys are outlined.

Analysis of Variance↗

PubMed2004

The effect of participation in the WIC program on preschoolers' diets.

OBJECTIVE: To evaluate nutrient, food intake, and snacking behavior by participation in the WIC (Special Supplemental Nutrition Program for Women, Infants, and Children) program. STUDY DESIGN: Secondary data analysis of a nationally representative cross-sectional survey conducted by USDA in 1994 to 1996 and 1998. METHODS: Statistical analysis was performed correcting for sample design effects and weighting for children in two income groups (<130%, n=1772 and 130% to 185% of poverty, n=689). RESULTS: Among WIC participants, the prevalence of snacking was significantly lower (68%) compared with nonparticipants (72%) (chi(2)=5.9, P=.01). For those <130% of poverty, WIC had a beneficial effect on the intake of fat, carbohydrates, added sugar, and fruit from the total diet as well as on added sugar from snacks. These were independent of food stamp participation. For those with higher incomes, the beneficial effects were limited to added sugar, iron density, and fruit intake for the total diet. A similar significant effect of decreased added sugar intake from snacks was also seen. CONCLUSIONS: Our results are in line with previous research showing beneficial effects of WIC participation among preschoolers, primarily for nutrients targeted by the program. This study shows that the effect can reach beyond those targeted nutrients.

Child Nutritional Physiological Phenomena↗

PubMedDate not supplied

Temporal and spatial distributions of contaminants in sediments of Santa Monica Bay, California.

Contaminant inputs from wastewater discharge, a major source of contamination to Santa Monica Bay (SMB), have declined drastically during the last three decades as a result of improved treatment processes and better source control. To assess the concomitant temporal changes in the SMB sediments, a study was initiated in June 1997, in which 25 box cores were collected using a stratified random sampling design. Five sediment strata corresponding to the time intervals of 1890-1920, 1932-1963, 1965-1979, 1979-1989, and 1989-1997 were identified using (210)Pb dating techniques. Samples from each stratum were analyzed for metals, 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites (DDTs), polychlorinated biphenyls (PCBs), and total organic carbon (TOC). Samples from the 1965-1979, 1979-1989, and 1989-1997 strata were also analyzed for polycyclic aromatic hydrocarbons (PAHs) and linear alkylbenzenes (LABs). Sediment metal concentrations increased from 1890-1979 and were similar during the time intervals of 1965-1979, 1979-1989, and 1989-1997, although the mass emissions of trace metals from sewage inputs declined substantially during the same time period. Trace organic contamination in SMB was generally highest in sediments corresponding to deposition during the years of 1965-1979 or 1979-1989 and showed a decline in concentration in the 1989-1997 stratum. Temporal trends of contamination were greatest in sediments collected from areas near the Hyperion Treatment Plant (HTP) outfall system and on the slope of Redondo Canyon. The highest contaminant concentrations were present in sediments near the HTP 7-mile outfall in the 1965-1979 stratum. Elevated trace metal and organic concentrations were still present in the 1989-1997 stratum of most stations, suggesting that sediment contaminants have moved vertically in the sediment column since sludge discharges from the 7-mile outfall (a dominant source of contamination to the bay) ceased in 1987. The widespread distributions of DDTs and PCBs in SMB and highly confined distribution of LABs around the HTP outfall system were indicative of a dispersal mechanism remobilizing historically deposited contaminants to areas relatively remote from the point of discharge.

California↗

PubMed1992

A comparison of psychosocial functioning and personality in amputee and chronic pain populations.

OBJECTIVE: To compare two populations with disabling conditions, amputation and chronic pain, in terms of psychosocial functioning and personality factors. We hypothesized that the degree of disability of amputees would resemble that of patients with chronic musculoskeletal pain. We also examined the prevalence of personality characteristics stereotypic of chronic pain in the two samples. DESIGN: Survey. SETTING: Outpatients at the pain and amputee clinics of a teaching hospital. PATIENTS: Ninety-four patients (47.7% of the number approached) were selected in consecutive samples taken from records and clinics. MAIN OUTCOME MEASURES: Sickness Impact Profile (SIP) and the Millon Clinical Multiaxial Inventory (MCMI). RESULTS: The two groups did not differ on the SIP total score. Sixteen of 47 amputees reported significant pain, and this group showed higher levels of overall disability than did patients with chronic musculoskeletal pain (n = 47) and significantly greater disability than the 31 amputees reporting low levels of pain. Contrary to common perceptions of chronic pain patients, 25% showed no significant evidence of psychopathology. Only anxiety and dysthymia levels were clinically elevated in more than 50% of chronic pain patients. CONCLUSIONS: Results are discussed in terms of the dual disability of amputees with chronic pain and of the hazards of attributing common characteristics to heterogenous patient groups.

Adult↗

PubMedDate not supplied

Evaluation of the Gen-Probe PACE 2 and the Microtrak enzyme immunoassay for diagnosis of Chlamydia trachomatis in urogenital samples.

BACKGROUND AND OBJECTIVES: The aim of the study was to investigate the value of the Gen-Probe PACE 2 assay for routine diagnosis of Chlamydia trachomatis in genital specimens of symptomatic and asymptomatic men and women patients. STUDY DESIGN: Samples were collected from 90 men and 299 women patients and tested by using the Gen-Probe assay and the EIA MicroTrak. Discrepant results were further analyzed by immunofluorescence, a second run of the Gen-Probe assay, and a probe competition assay (PCA) to establish the number of true positive and negative outcomes based on the two tests used. RESULTS: The overall prevalence of C. trachomatis was 8.5% in all patients tested (women: 3.7%, men: 13.3%) with an overall agreement of 95.4% between the two diagnostic methods. Of the 18 discordant results, 12 (67%) were considered to be false positive in the Gen-Probe assay and 3 (16%) false positive in the EIA. Two (11%) positive results were missed in the Gen-Probe assay and 1 (6%) in the EIA, all observed in female specimens. The sensitivities and specificities of the EIA were 91.7% and 100% for men and 100% and 99% for women, and for the Gen-Probe assay were 83.3% and 100% for men and 100% and 95.8% for women, respectively, when compared with true positive and true negative results. Although the predictive value for all positive results (PVP) was 88% for the EIA and 78.2% for the Gen-Probe assay, it was only 47.8% for positive female samples when using the Gen-Probe assay. CONCLUSION: The Gen-Probe assay revealed a sensitivity comparable with the EIA. The accuracy of test results provided by a single Gen-Probe assay was considerably lower than by Micro-Trak reducing the utility of PACE 2 as a diagnostic technique for Chlamydia diagnosis. Due to the high rate of false-positive samples in the Gen-Probe assay, positive results with a low value of relative light units have to be further analyzed by confirmation procedures.

Chlamydia Infections↗

PubMed2006

Development of an efficient sampling strategy to predict enoxaparin pharmacokinetics in stage 5 chronic kidney disease.

Patients with renal dysfunction are at greater risk for hemorrhagic events than patients with normal renal function. The objective of this study was to develop an efficient sampling strategy that optimally predicts anti-Xa activity exposure after enoxaparin administration in patients with chronic kidney disease to optimize enoxaparin therapy. The antifactor Xa activity data of 8 anuric patients who were administered 1 mg/kg enoxaparin immediately after hemodialysis were used for the development of the optimal sampling strategies. Maximum A Posteriori Bayesian (MAPB) priors were developed by pharmacokinetic analysis. The 2, 3, and 4 D-optimal sampling designs were determined and Monte Carlo simulations using the MAPB estimator were performed. The original model with the estimator was used to determine the predictive power of the sampling schemes. The most efficient sampling scheme (OSS-2) was accurate and precise in predicting apparent enoxaparin clearance (-3.2% bias, 6.5% precision). The addition of a third sampling time at 30 minutes (OSS-3) was more accurate (P < 0.01) and precise (P < 0.01) than OSS-2 at predicting the rate of absorption (ka) but did not improve the accuracy (P > 0.05) or precision (P = 0.20) of the CLs/F estimate. The determination of antifactor Xa activity at 5 and 24 hours, along with the Bayesian estimators generated from this study, accurately and precisely predict the apparent clearance of antifactor Xa activity. This sampling strategy may be used for therapeutic drug monitoring of enoxaparin and for future clinical trials in patients with chronic kidney disease.

Adult↗

PubMed2006

Intrauterine lignocaine as an anaesthetic during endometrial sampling: a randomised double-blind controlled trial.

OBJECTIVE: To evaluate the effectiveness of intrauterine lignocaine as an anaesthetic during endometrial sampling. DESIGN: Prospective, randomised, double-blind, placebo-controlled trial. SETTING: Outpatient gynaecological minor operation unit in a public hospital. POPULATION: Two hundred premenopausal women scheduled for endometrial sampling because of abnormal uterine bleeding. METHODS: Transcervical intrauterine instillation of 5 mL of 2% lignocaine or 5 mL of normal saline before performing endometrial sampling with vacuum aspirator. MAIN OUTCOME MEASURES: Evaluation of pain associated with the procedure using a visual analogue scale. RESULTS: The use of intrauterine lignocaine reduced pain during suction curettage in endometrial sampling. CONCLUSIONS: Transcervical instillation of lignocaine reduced pain during endometrial sampling.

Adult↗

PubMed1984

Multiexponential, multicompartmental, and noncompartmental modeling. II. Data analysis and statistical considerations.

Sums-of-exponentials models are widely used in biomedical research, chiefly as models of data, despite a sizable folklore criticizing their usefulness. Problems in multiexponential model fitting are addressed here, along with an exposition of how to quantify them and critically assess their quality with available statistical methods and computer programs. This class of models also is reconciled with two classes of models of systems: multicompartmental and noncompartmental models. Key issues include the importance of choosing a correct data error model, the necessity for computing model precision estimates, and the distinction between problems due to experiment design or overparameterization and purported difficulties with multiexponential models. Methods for obtaining statistical estimates of model precision, for checking goodness of fit of competing models, and for improving sampling designs are presented. Also the classic Lanczos problem is revisited, and some difficulties are resolved with a more efficient experiment design.

Models, Biological↗

PubMed1999

[Women's opinion about their health: a qualitative study].

OBJECTIVE: To find out what urban low and middle class women think about the relationship between health and daily behaviours, their social and family situation and the setting in which they live. DESIGN: Qualitative methodology and the focus group technique. SETTING: Urban population. PARTICIPANTS: Low and middle class women aged between 25 and 45. MEASUREMENTS AND MAIN RESULTS: For the sample design homogeneity variables (applicable to the whole group) such as socio-economic level and age were chosen and for heterogeneity variables (only applicable to some of the group's participants) motherhood and paid work outside the home. Two focus groups were conducted. For the analysis the opinions expressed by the women were identified, and were classified according to the scheme that the study group had made previously. Opinions were identified on the importance of food and information about it, concern for their children and for the options provided for the establishment of healthy lifestyles. Only the group of low socioeconomic level identified money as relevant for access to health services. No reference was made to smoking and alcohol. Mental health aspects were predominant. CONCLUSIONS: The opinions of women about aspects which influence their health differ according to social class. The factors identified by scientific literature are not a priority for them. They are not necessarily concerned about health problems with highest mortality and morbility.

Adult↗