Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “sampling design”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources
PubMed1998

An in situ nanoindentation specimen holder for a high voltage transmission electron microscope.

We describe in detail, the design, construction, and testing of a specimen holder that allows for the nanoindentation of surfaces while viewing in cross-section in a high voltage transmission electron microscope (TEM). This nanoindentation specimen holder, having three-axis position control of a diamond indenter in combination with micromachined specimens, allows for the first time the dynamic observation of subsurface microstructure evolution under an indenter tip. Additionally, the sample design techniques that have been developed for these procedures may eliminate the need for TEM specimen preparation for additional ex situ nanoindentation experiments. Initial experimental results from in situ indentation of Si samples in the high voltage electron microscope are reported here to demonstrate the capability of this new specimen holder.

Crystallization↗
PubMed1997

Shelter-based homeless youth. Health and access to care.

OBJECTIVES: To compare the self-reported risk-taking behaviors, health status, and access to care issues of 2 samples of shelter-based homeless youth who had previously been street youth (youth on streets or doubling-up with friends or lovers) and systems youth (youth involved in foster care) and to examine information on the etiology of homelessness, including parent or family of origin risk factors for both samples. DESIGN: The study population consisted of 109 shelter-based homeless youth: 41 street youth and 68 systems youth. A chart audit was completed on all youth, noting documentation of past health problems, reasons for shelter placement, and parental risk factors. Adolescents from both samples completed a health history questionnaire followed by a physical examination. Differences between the 2 samples for behaviors and disease diagnoses were examined using chi 2 and 2-tailed t tests. RESULTS: The street youth exhibited greater risk-taking behaviors and suffered from poorer health status and access to care than did systems youth. The main differences were in substance using and high-risk sexual behaviors. The street youth were more likely to report previous exposure to violence and having been victims of forced sex. Self-reported risk behaviors, including sexual activity and substance abuse were corroborated by more objective information on these items from medical record information. The street youth were more likely to be medically uninsured, to have used an emergency department in the past year, and to have used an emergency department for their last care. CONCLUSIONS: There are important variations in health needs between samples of homeless youth, often overlooked in health planning for this population. Knowledge of parent or family of origin risk factors and causes of homelessness provides important contextual information for understanding the risk behaviors and health states of homeless youth.

Adolescent↗
PubMed1982

Sister chromatid exchanges induced in rabbit lymphocytes by ethylene oxide after inhalation exposure.

Ethylene oxide, which is the simplest epoxide and an extremely important commercial compound, has been used by many investigators as a model compound to study mutagenicity by alkylation of DNA. Knowledge of in vivo dose-effect relations under experimental conditions may provide further insight into the dynamics of the sister chromatid exchange (SCE) response. It may also provide information on temporal aspects of sampling design for human worker populations. Groups of four male New Zealand white rabbits were exposed in inhalation chambers to 0, 10, 50, and 250 parts per million (ppm) ethylene oxide for 6 hr a day, 5 days a week, for 12 weeks. Peripheral blood samples were taken before the start of exposure, at intervals during exposure, and up to 15 weeks after the end of exposure to measure SCE rates in peripheral lymphocytes as well as standard hematological endpoints. Additionally, the level of reduced glutathione (GSH) in liver and blood was measured in a set of concurrently exposed animals at the end of the 12-week exposure. Results show that exposure to 10 ppm does not cause a detectable increase in SCE rates. However, exposure to 50 and 250 ppm does cause an increase in SCEs that decreases after exposure ends, but still remains above baseline levels 15 weeks after exposure. Hematological and GSH measurements did not differ between control and exposed groups. These results indicate that inhalation exposure to the mutagenic alkylating agent ethylene oxide results in a dose-related SCE effect, and that SCE is a more sensitive indicator of exposure than either standard hematological end points or GSH levels.

Animals↗
PubMed2006

Limited sampling strategy for predicting area under the concentration-time curve of mycophenolic acid in adult lung transplant recipients.

STUDY OBJECTIVE: To develop limited sampling strategies for estimation of mycophenolic acid exposure (by determining area under the concentration-time curve [AUC]) in lung transplant recipients by using sampling times within 2 hours after drug administration and a maximum of three plasma samples. DESIGN: Prospective, open-label clinical study. SETTING: Lung transplant clinic in Vancouver, British Columbia, Canada. PATIENTS: Nineteen adult (mean age 48.3 yrs) lung transplant recipients who were receiving mycophenolate mofetil therapy along with cyclosporine (9 patients) or tacrolimus (10 patients). INTERVENTION: Eleven blood samples were collected from each of the 19 patients over 12 hours: immediately before (0 hr) and 0.3, 0.6, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after administration of mycophenolate mofetil. MEASUREMENTS AND MAIN RESULTS: Mycophenolic acid levels in plasma were determined by a high-performance liquid chromatography-ultraviolet detection method. The 19 patients were randomly divided into index (10 patients) and validation (9 patients) groups. Limited sampling strategies were developed with multiple regression analysis by using data from the index group. Data from the validation group were used to test each strategy. Bias and precision of each limited sampling strategy were determined by calculating the mean prediction error and the root mean square error, respectively. The correlation between AUC and single concentrations was generally poor (r2= 0.18-0.73). Two single-concentration strategies, eight two-concentration strategies, and eight three-concentration strategies matched our criteria. However, the best overall limited sampling strategies (and their predictive performance) were the following: log AUC = 0.241 log C0 + 0.406 log C2 + 1.140 (bias -5.82%, precision 5.97%, r2= 0.828) and log AUC = 0.202 log C0 + 0.411 log C1.5 + 1.09 (bias -5.71%, precision 6.94%, r2= 0.791), where Cx is mycophenolic acid concentration at time x hours. CONCLUSION: Two-concentration limited sampling strategies provided minimally biased and highly precise estimation of mycophenolic acid AUC in lung transplant recipients. These optimal and most clinically feasible limited sampling strategies are based collectively on the number of blood samples required, r2 value, bias, and precision.

Adult↗
PubMed2001

Heteroresistance in Mycobacterium tuberculosis.

SETTING: Drug resistance in Mycobacterium tuberculosis is often linked to specific mutations in a limited number of resistance genes. Detection of these mutations in a cultured isolate can predict the resistant phenotype. Genotypic analysis of the mycobacteria directly in a clinical specimen would result in considerable time saving for resistance prediction. OBJECTIVE: To find out whether resistance-predicting genotypes of mycobacteria found after cultivation always give a good reflection of those in the original clinical sample. DESIGN: Restriction fragment length polymorphisms of repetitive polymerase chain reaction (PCR) amplification and cloning of PCR products were used as nonintegrative methods to describe the composition of katG, rpsL and embB genotypes involved in resistance to isoniazid, streptomycin and ethambutol, respectively, in the original sample. This result was then compared to the phenotypic resistance profile after cultivation. RESULTS: Using both methods, mixed, heteroresistant populations could be detected in almost every fifth analyzed sample (katG: 5 of 16; rpsL: 3 of 17; embB: 1 of 21). Direct sequencing, a widely used integrative method, repeatedly failed to detect heteroresistance. CONCLUSION: Heteroresistance is a valid phenomenon in clinical tuberculosis. It is not rare and not restricted to a particular resistance gene, and is obscured by cultivation as well as by some, not all, culture-independent resistance prediction tests.

Antitubercular Agents↗
PubMed2006

Eight novel mutations in SPG4 in a large sample of patients with hereditary spastic paraplegia.

BACKGROUND: Hereditary spastic paraplegia (HSP) is a group of genetically heterogeneous disorders characterized by progressive spasticity of the lower limbs. Mutations in the SPG4 gene, which encodes spastin protein, are responsible for up to 45% of autosomal dominant cases. OBJECTIVE: To search for disease-causing mutations in a large series of Italian patients with HSP. DESIGN: Samples of DNA were analyzed by direct sequencing of all exons in SPG4. Samples from a subset of patients were also analyzed by direct sequencing of all exons in SPG3A, SPG6, SPG10, and SPG13. SETTING: Molecular testing facility in Italy. PATIENTS: Sixty unrelated Italian patients with pure (n = 50) and complicated (n = 10) HSP. MAIN OUTCOME MEASURES: Mutations in SPG4, SPG3A, SPG6, SPG10, and SPG13. RESULTS: We identified 12 different mutations, 8 of which were novel, in 13 patients. No mutations of any of the other HSP genes tested were found in 15 patients with sporadic pure HSP who did not have mutations in the SPG4 gene. CONCLUSIONS: The overall rate of mutation in the SPG4 gene within our sample was 22%, rising to 26% when only patients with pure HSP were considered. The negative result obtained in 15 patients without mutations in SPG4 in whom 4 other genes were analyzed (SPG3A, SPG6, SPG10, and SPG13) indicate that these genes are not frequently mutated in sporadic pure HSP.

Adenosine Triphosphatases↗
PubMed2003

Average volume of alcohol consumption and all-cause mortality in African Americans: the NHEFS cohort.

AIM: To analyze the relationship between average volume of alcohol consumption and all-cause mortality in African Americans. DESIGN: Prospective cohort study--the NHANES Epidemiologic Follow-Up Study (NHEFS)--with baseline data collected 1971 through 1975 as part of the first National Health and Nutrition Examination Survey (NHANES I) and follow-up through 1992. PARTICIPANTS: The analytic data set consisted of 2054 African American men (n = 768) and women (n = 1,286), 25 to 75 years of age, who were followed for approximately 19 years. MEASUREMENT: Alcohol was measured with a quantity-frequency measure at baseline. OUTCOME: All-cause mortality. RESULTS: No J-shaped curve was found in the relationship between average volume of alcohol consumption and mortality for male or female African Americans. Instead, no beneficial effect appeared and mortality increased with increasing average consumption for more than one drink a day. The reason for not finding the J-shape in African Americans may be the result of the more detrimental drinking patterns in this ethnicity and consequently the lack of protective effects of alcohol on coronary heart disease. Taking into account sampling design did not substantially change the results from the models, which assumed a simple random sample. CONCLUSIONS: If this result can be confirmed in other samples, alcohol policy, especially prevention, should better incorporate patterns of drinking into programs.

Adult↗
PubMedDate not supplied

National Immunization Survey: the methodology of a vaccination surveillance system.

The National Immunization Survey (NIS) was designed to measure vaccination coverage estimates for the US, the 50 states, and selected urban areas for children ages 19-35 months. The NIS includes a random-digit-dialed telephone survey and a provider record check study. Data are weighted to account for the sample design and to reduce nonresponse and non-coverage biases in order to improve vaccination coverage estimates. Adjustments are made for biases resulting from nonresponse and nontelephone households, and estimation procedures are used to reduce measurement bias. The NIS coverage estimates represent all US children, not just children living in households with telephones. NIS estimates are highly comparable to vaccination estimates derived from the National Health Interview Survey. The NIS allows comparisons between states and urban areas over time and is used to evaluate current and new vaccination strategies.

Data Collection↗
PubMed2005

Predicting outcomes after hip fracture repair.

OBJECTIVE: To compare the activities of daily living before and after hip fracture and construct a statistical model for discharge destination and independent walking. The classification accuracy of the model was determined from an independent sample. DESIGN: Prospective study: FIM prefracture, at discharge, and at 6-mo follow-up were obtained from 63 patients who underwent operations for acute hip fractures. A statistical model for discharge destination and independent walking was made and classification accuracy was checked using 78 independent samples. RESULTS: The motor FIM scores at prefracture decreased significantly at discharge (P < 0.0001) and at 6-mo follow-up (P < 0.0001), but at 6-mo follow-up, they had increased significantly compared with those at discharge (P = 0.0103). A mobility subscale was used to predict discharge destination, and mobility and social cognition subscales were related to independent walking. The predictive accuracy was 87%. CONCLUSIONS: Motor FIM scores increase for at least 6 mos after hip fracture, and discharge destination and independent walking were highly predictable from FIM mobility and social cognition subscales.

Activities of Daily Living↗
PubMed2005

Differential trappability of small mammals in three habitats of Southeastern Brazil.

We compared the trappability of marked and unmarked individuals in species of marsupials and rodents of three tropical assemblages of small mammals in Brazil. Two studies used trapping grids, one in cerrado and the other in an Atlantic forest reserve, whereas the study in a rural area used transects. In the two studies using trapping grids, marked animals were frequently more trappable than unmarked ones, but in some species this difference was not significant. In the rural area, marked and unmarked animals did not differ significantly. The number of recaptures per resident animal was higher in the two studies using trapping grids than in the rural area where transects were used. Differences in trappability between the three studies might have been caused by differences not only in trapping design (grids vs. transects), but also in the type of trap used, bait, and habitat. Although differential trappability tends to be considered the rule in small mammals, these results suggest that trappability of marked and unmarked animals may be specific for the particular combination of sampling design, field methods, and habitat under study.

Animals↗
PubMed1998

Choice of sugar-free medicines by a sample of dentists, doctors and pharmacists in Northern Ireland: the views of parents and health professionals.

OBJECTIVE: To determine the sources of learning and the levels of support concerning sugar-free medicines by doctors and pharmacists, to examine the provision of choice from the viewpoints of professionals and the parents, and to test the sugar-free status of medication in tests of prescribing. DESIGN: Samples of health professionals comprising 47 general medical practitioners, (87% response rate) 29 pharmacists (94%) and 25 general dental practitioners (100%) completed closed questionnaires as did 209 parents (72%) of 4-year-old children. SETTING: Newry and Mourne Health Trust Area, Northern Ireland. OUTCOME MEASURES: Proportions of respondents citing various learning sources and the levels of support for the use of sugar-free medicines were obtained and the proportions of doctors and pharmacists claiming to offer various frequencies of choice were compared to the proportions of parents recalling receiving such choices. Test prescriptions were examined and the sugar-free status of the prescribed medication was determined. RESULTS: Markedly different sources of learning were cited by different groups. Ninety per cent of pharmacists and 88% of dentists believed that medication should be in sugar-free form in all cases, while only 66% of doctors thought so. Forty three per cent of doctors claimed to always offer a choice while 17% of parents recalled receiving this. The equivalent figures for pharmacists and parents were 69% and 11%. The majority of test prescriptions by doctors and dentists were for sugar containing medicines.

Attitude of Health Personnel↗
PubMed2006

TuBaFrost: European virtual tumor tissue banking.

TuBaFrost is a consortium responsible for the task to create a virtual European human frozen tumor tissue bank, composed of high quality frozen tumor tissue collections with corresponding accurate diagnosis stored in European cancer centers and universities, searchable on the Internet, providing rules for access and use and a code of conduct to comply with the various legal and ethical regulations in European countries. Such infrastructure would enlarge tissue availability and accessibility in large amounts of specified or even rare tumor samples. Design of an infrastructure for European residual tissue banking with the described characteristics, clear focus points emerge that can be broken down in dedicated subjects: (1) standardization and quality assurance (QA) to avoid inter-institute quality variation; (2) law and ethics enabling exchange of tissue samples possible between institutes in the different European countries, where law and ethics are characterized by a strong variability; (3) rules for access, with sufficient incentives for collectors; (4) central database application containing innovations on search and selection procedures; (5) support when needed with histology images; and (6) Internet access to search and upload, with in addition a solid website giving proper information on the procedures, intentions and activities not only to the scientific community, but also to the general public. One consortium decision, part of the incentives for collectors, had major impact on the infrastructure; custodianship over the tissues as well as the tissues stay with the collector institute. Resulting in specimens that are not given to an organization, taking decisions on participation of requests, but instead the local collected tissues stay very easy to access by the collector and allows autonomous negotiation between collector and requestor on cooperation, coauthorship in publication or compensation in costs. Thereby, improving availability of large amounts of high quality samples of a highly specified or rare tumor types and contact opportunities for cooperation with other institutes.

Databases, Factual↗
PubMed1994

Quality of life after spinal cord injury: a literature critique and meta-analysis (1983-1992).

Research articles cross-indexed in Index Medicus under the subject headings "quality of life" (QOL) and "spinal cord injury" (SCI) were examined in order to compare their relative merits in terms of research design, sampling techniques and the type of QOL criteria included. Of 3,710 citations indexed for the ten year period 1983 through 1992 under "quality of life," thirty-two research articles (< 1 percent) were cross-indexed with the subject heading "spinal cord injury." The modal design was a descriptive survey or case study (n = 23 or 72 percent). None of them were randomized clinical trials. Because of limited rigor of research design and poor validity of measurements, conclusions about the ability of rehabilitative care to improve the QOL for SCI persons could not be drawn from the studies reviewed. Meta-analysis indicated that severity of injury is associated with QOL, with more severe injury being correlated with poorer quality. The critique concludes that QOL research with SCI persons needs to be better designed and should include more uniform and valid criteria.

Disability Evaluation↗
PubMed2000

The Child Health Questionnaire in Australia: reliability, validity and population means.

OBJECTIVE: To provide reliability, validity and population means for the Australian Authorized Adaptation of the parent-report Child Health Questionnaire (CHQ). METHOD: We surveyed a representative sample of Australian parents of school-aged children (5-18 years) in Victoria between July and December 1997, using a school-based cluster sample design stratified by educational sector and age. RESULTS: Some 5,414 parents responded (72%). Good psychometric performance was observed for the CHQ in Australia. Population means demonstrated differences in health on domains of functioning and well-being by age and gender. This population-derived sample demonstrated high ceiling values on Physical Functioning and Social Role scales. IMPLICATIONS: The CHQ appears to be a reliable and valid measure of child and adolescent functional health and well-being for the Australian population. Child health outcomes of children and adolescents with particular conditions or within population subgroups can be compared with these age and gender benchmarks. Appropriate uses for the CHQ may be to discriminate between children who are generally healthy and children with health problems, or in population surveys partnered with measures that extend the range of physical functioning and social functioning.

Activities of Daily Living↗
PubMedDate not supplied

Hydroacoustic estimation of fish biomass in the Gulf of Nicoya, Costa Rica.

A stratified sampling design was used for a hydroacoustic survey of the inner parts of the Gulf of Nicoya in 1987 and 1988. The bottom topography of the inner Gulf was modeled by introducing the concept of a topographical basin model, as the basis for the projection of the sample survey estimates to the entire inner gulf. The bottom depth contours and volumes for the basin model were constructed from nautical charts. The estimates of sample abundance were made for the fish in the inner Gulf using the acoustic methods, EMS (Expectation Maximization and Smoothing) and echo integration. The estimates of population were made by the multiplication of the topographic model's estimate of water volume and a model of fish density dependent on bottom depth. The results showed a general decrease in fish density biomass with bottom depth, and a simultaneous tendency for maximum concentrations over bottom depths of about four meters. The four meter bottom depth includes a broad expanse of the inner Gulf located south of Isla Chira. Overall estimates of volumetric density (0.269 fish/m3) and of areal densities (1.88 fish/m2) are comparable to other estuarine shallow water environments.

Acoustics↗
PubMed2004

Cortisol and catecholamines in posttraumatic stress disorder: an epidemiologic community study.

BACKGROUND: Prior research has connected posttraumatic stress disorder (PTSD) to increased levels of catecholamines. However, studies of cortisol levels have produced mixed results. OBJECTIVE: To examine urinary catecholamine and cortisol levels in individuals with PTSD in a community sample. DESIGN: A representative cohort of young adult community residents, assessed periodically during a 10-year period for exposure to trauma and PTSD, was used to select a subset for urine collection studies conducted in a sleep laboratory across 2 consecutive nights and the intermediate day. SETTING: The sample of young adults was randomly selected from a large health maintenance organization and is representative of the geographic area except for the extremes of the socioeconomic status range. PARTICIPANTS: A subsample was selected from the 10-year follow-up cohort (n = 913; 91.1% of the initial sample). Eligibility criteria were: (1) persons exposed to trauma during the preceding 5 years, (2) other individuals who met PTSD criteria, and (3) a random preselected subsample. Of 439 eligible individuals, 292 (66.5%) participated, including 69 with lifetime PTSD. MAIN OUTCOME MEASURES: Measures of cortisol and catecholamine levels in urine. RESULTS: The lifetime PTSD group demonstrated significantly higher catecholamine levels than the group exposed to trauma without PTSD and the nonexposed group. Individuals exposed to trauma without PTSD demonstrated significantly lower urine catecholamine levels than the nonexposed and the PTSD groups. Mean cortisol levels did not differ across groups. When analyzed by comorbidity with major depressive disorder (MDD), the PTSD-only group did not differ in cortisol levels from the groups with neither PTSD nor MDD. Women with MDD plus PTSD demonstrated significantly higher cortisol levels than women with neither disorder or with either disorder alone. CONCLUSIONS: Trauma per se does not lead to sustained increases in cortisol or catecholamine levels. Posttraumatic stress disorder is associated with higher catecholamine levels. In contrast, persons with PTSD had neither an increase nor a decrease in mean urinary cortisol levels. Women with PTSD and comorbid MDD had higher cortisol levels.

Adult↗
PubMed1996

Bayesian inference on prevalence using a missing-data approach with simulation-based techniques: applications to HIV screening.

Health departments and other health-related authorities seek accurate assessment of the spread of human immunodeficiency virus (HIV) among populations. Although screening for HIV provides a direct means for estimating its prevalence, it is complicated by the heterogeneity of available diagnostic tests and the degree to which they can diagnose HIV accurately. To integrate the limited precision of screening tests with prior results, Bayesian inference becomes a method of choice. Current Bayesian methods, however, have limited applications and do not readily generalize for complicated sampling designs and for modelling needs, particularly those that relate to HIV screening. By utilizing recent developments in the theories of missing-data analysis and simulation-based techniques, we develop an approach to Bayesian analysis of prevalence. This methodology is quite general for a variety of sampling schemes and sufficiently flexible to accommodate various practical considerations that arise from HIV screening. We illustrate the methodology with real as well as simulated data sets. Further, by utilizing the methodology, we performed simulations to demonstrate that pooled testing provides a cost-effective means to improve the precision of estimates of prevalence under the currently limited screening technology.

Algorithms↗
PubMed2005

An in vivo evaluation of induction of abnormal sperm morphology in mice by landfill leachates.

Although several reports have demonstrated the acutely toxic and genotoxic effects of landfill leachates in microbial organisms, plants and aquatic animals, the effects of pollutants present in these leachates have not been clarified yet in terrestrial animals. This study mainly aimed to evaluate a potential genetic effect of raw and simulated leachates from Orita-Aperin and Oworonsoki landfills in south-west Nigeria by use of the murine sperm-head abnormality test. These landfills neither have a synthetic membrane liner at the bottom, nor a natural layer of compacted soil with the desired hydraulic conductivity, nor a run-off control system. As a result, the leachates produced are discharged into the environment. Samples designated as Orita-Aperin Raw Leachate (OARL), Orita-Aperin Simulated Leachate (OASL), Oworonsoki Raw Leachate (OWRL) and Oworonsoki Simulated Leachate (OWSL) were analyzed in the sperm-head abnormality test at concentrations (v/v) of 1%, 2.5%, 5%, 10% and 25%. Mice were given 0.5 ml sample per day for five consecutive days by intraperitoneal injection. Each dose group comprised seven mice, and a 5-week exposure period was utilized. The data show that the test mixtures induced a dose-dependent, statistically significant increase (P<0.05) in the number of sperm with abnormal morphology. Physico-chemical analysis of the test samples shows that they contained constituents that are capable of inducing mutation in biologic system. The interaction of some of these constituents with the genetic material in the differentiating cells during spermatogenesis may be responsible for these observations. This is relevant in environmental waste management, and for the assessment of the hazardous effects of the chemicals in landfill leachates.

Animals↗