SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Abstract: The National Immunization Survey (NIS) is a large federally funded survey designed to estimate vaccination coverage rates for children residing in the United States aged 19 to 35 months. In 1999, over 8 million telephone call attempts were made to obtain provider-reported vaccination histories on 22,521 children in the age range of interest.
This paper considers a model for the difference of two proportions in a paired or matched design of clinical trials, case-control studies and also sensitivity comparison studies of two laboratory tests. This model includes a parameter indicating both interpatient variability of response probabilities and their correlation. Under the proposed model, we derive a one-sided test for equivalence based upon the efficient score. Equivalence is defined here as not more than 100 delta per cent inferior. McNemar's test for significance is shown to be a special case of the proposed test. Further, a score-based confidence interval for the difference of two proportions is derived. One of the features of these methods is applicability to the 2 x 2 table with off-diagonal zero cells; all the McNemar type tests and confidence intervals published so far cannot apply to such data. A Monte Carlo simulation study shows that the proposed test has empirical significance levels closer to the nominal alpha-level than the other tests recently proposed and further that the proposed confidence interval has better empirical coverage probability than those of the four published methods.
The importance of considering statistical power in marine pollution studies is unequivocal. However, the vast majority of ecological literature on power analysis focuses on parametric rather than non-parametric tests. This note describes a Monte Carlo simulation method for estimating the power of non-parametric tests. The method is illustrated using ordinal data.
It has long been the goal of biomaterials research in the field of orthopedics to develop synthetic structures exhibiting comprehensive bioactivity. In particular, an ideal bone-biomaterial would support the activity of osteoblasts in the development of new bone, while simultaneously being resorbed by osteoclasts as part of the lifelong orderly process of bone remodelling. Such resorbable calcium phosphate-based thin films and bulk ceramics have now been created by the high-temperature processing of a fine precipitate, formed from a colloidal sol and stabilized using an additive such as silicon. The materials have two characteristic features: a phase composition which is a mixture of calcium hydroxyapatite and a silicon stabilized tricalcium phosphate, and a microporous morphology based on inter-connected particles (0.2-1 microm in diameter). X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and light scattering experiments indicate that the characteristic phase composition arises during sintering through substitution reactions where silicon enters the calcium phosphate lattice under conditions of high chemical reactivity. The crystallographic features are linked through the glaserite form of the apatite structure.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Measurements of the cerebral cortical volume used to be very laborious, due to the 3-D complexity of the gyral pattern. Using stereological methods, which allow the quantification of 3-D structures from measurements on 2-D cross-sections, the difficulties have been overcome. In thirty formalin-fixed normal human brains the total volumes were measured by saline displacement. The brains were serially sliced in coronal sections and the fractional areas of the cortex, white matter, central grey structures and ventricles were determined by point-counting. Using Cavaliéri's principle the volumes of these structures were calculated. The average cortical fixed volume was 549 ml (SD +/- 107) corresponding to 54% of the total volume of the hemispheres. The coefficient of error of the cortical volume determinations was 2.6%. The efficiency of the design and the possibilities for optimizing the design are discussed. This point-counting method was preferred to the use of an automatic image analyser, being precise, easy to handle and not interfering with further tissue processing for histological preparation.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The temporal variation in the concentrations of particulate trace metals (Cu, Pb and Zn) and total suspended solids (TSS) was examined in three rivers that drain into the Port Jackson estuary, Australia, using a nested, hierarchical sampling design. Sampling was conducted between March and June 1999, under low flow conditions. The sampling design incorporated four temporal scales (hours, days, weeks and months). It was considered that hours, days, weeks and months were representative of such time scales and could be analyzed as random, nested sources of variation in an analysis of variance (ANOVA). Significant variation was found at temporal scales ranging from hours, within the same day, to months. The amount and scales of variation differed between particulate trace metals and TSS concentrations and between rivers. In many cases, differences between small-scale were as important as differences between months. The results suggest that higher anthropogenic influences cause higher variability at small temporal scale. Results indicate the need for nested sampling designs to be incorporated into studies of temporal variation in order to unconfound small-scale temporal variation. The conclusions of this study are likely to be applicable to other water quality variables and pollutants.
Multiple data sources are sometimes available as potential sampling frames for population surveys, and in some situations the use of a multiple frame sample design is more advantageous than using a single sampling frame. The use of multiple sampling frames, however, has variance and bias implications, as well as sampling, data collection, and logistical considerations. These issues are addressed for a proposed dual frame sampling approach in the National Health Interview Survey (NHIS). The results of an investigation of the sampling efficiencies and operational issues in supplementing the NHIS area frame sample with a sample of elderly African and Hispanic Americans and persons with disabilities selected from Social Security Administration files are presented.
Kinships composed of twin parents, their spouses and children, offer a robust and flexible sampling design for research in genetic epidemiology. Families-of-twins designs circumvent some of the sampling problems that arise when independent data sets are combined, and these designs provide unique evaluations of maternal influences, assortative mating and X-linkage. Unfortunately, empirical studies of families of twin parents have been limited by relatively small samples and by the self-selection biases intrinsic in ascertainment of families from volunteer twin registries. A large and representative cohort of monozygotic and dizygotic twin parents, drawn from a population-based twin registry, provides the optimal sampling frame for twin-family research. This paper reviews the sampling considerations underlying the initial family study based on the Finnish Twin Cohort and evaluates the representativeness of the sampled twins. Spouses and adult children (over 18 years) of 236 pairs of twins, about equally divided by gender and zygosity, were evaluated by a postal questionnaire. Individual response rates exceeded 86% and in 464 of the 472 nuclear families (98.3%), at last one member of the twin's family completed the questionnaire. The sampled twins, selected for fecundity to maximize statistical power of the obtained data, were broadly representative of non-selected twins drawn from the Cohort, with whom they were matched on age, gender, and zygosity. Such results suggest that the Finnish Cohort has excellent potential for extended twin-family research designs.
Immature density and population size of the biting midge Culicoides belkini (Wirth & Arnaud) were estimated for habitats on Moorea Island, French Polynesia, by means of random, 2- and 3-stage sampling designs. Samples were taken in March 1993 from 5 strata of a large larval habitat: a sandy-mud surface of approximately 5,000 m2 (stratum 1) in which approximately 12,000 land crab burrows (stratum 2) were counted, a small pond surrounded by approximately 300 m2 of muddy bank (stratum 3), and a high organic muddy area (Kopara) of approximately 1,200 m2 (stratum 4) with approximately 3,500 crab burrows (stratum 5). Larval density was usually higher in the mud of crab burrows, especially those in the Kopara stratum. Larval density was significantly lower in the sediment of the sandy area as compared with pond banks or Kopara surface. The sampling designs and techniques were logistically adequate, statistically relevant, and were recommended for future studies on C. belkini larval density. Larval habitats were characterized by means of multivariate analysis. Comparison of larval densities with selected environmental variables indicated that larvae density was higher in wet sediments with high levels of organic matter (approximately 8% of dry weight of sediment) and low salinity (approximately 0.5-1.5% NaCl equivalents). These variables were considered significant if larval control by means of habitat modification has to be achieved. Nevertheless, C. belkini can tolerate a broad spectrum of variation in the other environmental variables measured and breed in a variety of ecological situations. Therefore, it has a high potential for colonizing new habitats.
The "activities of daily living," or ADLs, are the basic tasks of everyday life, such as eating, bathing, dressing, toileting, and transferring. Reported estimates of the size of the elderly population with ADL disabilities differ substantially across national surveys. Differences in which ADL items are being measured and in what constitutes a disability account for much of the variation. Other likely explanations are differences in sample design, sample size, survey methodology, and age structure of the population to which the sample refers. When essentially equivalent ADL measures are compared, estimates for the community-based population vary by up to 3.1 percentage points; and for the institutionalized population, with the exception of toileting, by no more than 3.2 percentage points. As small as these differences are in absolute terms, they can be large in percent differences across surveys. For example, the National Medical Expenditure Survey estimates that there are 60 percent more elderly people with ADL problems than does the Supplement on Aging.