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 487 records · Page 27Linked to original sources
PubMed2002

Does fear of childbirth during pregnancy predict emergency caesarean section?

OBJECTIVE: Caesarean section rates are rising dramatically in the UK. It has been estimated that they have increased from 10% to 22% of all births over 15 years. A Swedish study has suggested that fear of childbirth during pregnancy may increase the risk of emergency caesarean section. The aim of this study is to identify whether fear of childbirth can predict the occurrence of emergency caesarean section in a UK sample. DESIGN: A prospective design using between-group comparisons. SETTING: Sheffield. S. Yorkshire, UK. SAMPLE: Four hundred and forty-three pregnant women, recruited at 32 weeks of gestation, over 16 years of age. METHODS: Participants completed self-assessment, postal questionnaires assessing fear of labour and anxiety using the Wijma Delivery Expectancy Scale (W-DEQ) and the Speilberger State Trait Anxiety Scale (STAI), together with their expectations about their mode of delivery. Delivery information was gathered via birth summary sheets. MAIN OUTCOME MEASURE: Mode of delivery. RESULTS: Emergency caesarean section was associated with previous caesarean section, parity, age and a score reflecting medical risk, but not fear of childbirth or anxiety measures. There were no differences in fear between women experiencing spontaneous-vertex, forceps/ventouse, emergency or elective caesarean deliveries. The W-DEQ was factor analysed and was found to measure four distinct domains: fear, lack of positive anticipation and the degree to which women anticipate isolation and riskiness in childbirth. However, these individual factors also failed to contribute to the prediction of mode of delivery. Primiparous women in the UK sample showed highly elevated fear scores when compared with a Swedish sample. Such discrepancies were not found for the multiparous sample. CONCLUSIONS: Fear of childbirth during the third trimester is not associated with mode of delivery in a UK sample. Possible cross-cultural differences are discussed.

Adolescent↗
PubMed1991

A measuring technique for the investigation of the dielectric behaviour of biological tissue at low temperatures.

The experimental technique described can be used to measure the complex dielectric constant of different kinds of samples in the temperature range T = 300 to 4K. The specially designed sample holder guarantees simple preparation and allows in-vitro measurements of biological tissues as well as investigations of related materials of interest including liquids. The results of fatty tissue chosen as a model substance will be shown and discussed in comparison to simple basic compounds in subsequent papers.

Electric Conductivity↗
PubMed1979

An investigation of coronary heart disease in families. The Framingham offspring study.

The Framingham Heart Study (FHS) was started in 1948 as a prospective investigation of cardiovascular disease in a cohort of adult men and women. Continuous surveillance of this sample of 5209 subjects has been maintained through biennial physical examinations. In 1971 examinations were begun on the children of the FHS cohort. This study, called the Framingham Offspring Study (FOS), was undertaken to expand upon knowledge of cardiovascular disease, particularly in the area of familial clustering of the disease and its risk factors. This report reviews the sampling design of the FHS and describes the nature of the FOS sample. The FOS families appear to be of typical size and age structure for families with parents born in the late 19th or early 20th century. In addition, there is little evidence that coronary heart disease (CHD) experience and CHD risk factors differ in parents of those who volunteered for this study and the parents of those who did not volunteer.

Adult↗
PubMed2006

HIV prevalence and sexual risk behaviors among men who have sex with men: results from a statewide population-based survey in California.

OBJECTIVES: To investigate HIV prevalence, sexual risk behaviors, and HIV testing among men who have sex with men (MSM) between 18 and 64 years old living in California. DESIGN: Cross-sectional study of a statewide population-based sample of MSM. METHODS: Using data from the 2001 California Health Interview Survey (CHIS 2001), 398 men who self-identified as gay or bisexual were recontacted and interviewed by telephone for a follow-up study in 2002. Study participants were interviewed regarding their demographic characteristics and sexual behavior, HIV testing history, and HIV infection status. Those who self-reported as HIV-negative or of unknown status were offered an HIV test using a home urine specimen collection kit. RESULTS: HIV prevalence among MSM in California was 19.1% (95% confidence interval [CI]: 12.8% to 25.3%) with higher rates seen among the following subgroups: high school or less education (40.4%), annual income less than dollar 20,000 (35.0%), or history of ever injecting recreational drugs (40.3%). Young age and Hispanic or African-American race/ethnicity were associated with higher proportions of risky sexual behavior and lower HIV testing rates. CONCLUSIONS: HIV prevalence among MSM living in California continues to be high across the whole state, and population-based studies are needed periodically to complement findings from surveys using other sampling designs.

Adolescent↗
PubMed2005

The effects of geography and spatial behavior on health care utilization among the residents of a rural region.

OBJECTIVE: This analysis determines the importance of geography and spatial behavior as predisposing and enabling factors in rural health care utilization, controlling for demographic, social, cultural, and health status factors. DATA SOURCES: A survey of 1,059 adults in 12 rural Appalachian North Carolina counties. STUDY DESIGN: This cross-sectional study used a three-stage sampling design stratified by county and ethnicity. Preliminary analysis of health services utilization compared weighted proportions of number of health care visits in the previous 12 months for regular check-up care, chronic care, and acute care across geographic, sociodemographic, cultural, and health variables. Multivariable logistic models identified independent correlates of health services utilization. DATA COLLECTION METHODS: Respondents answered standard survey questions. They located places in which they engaged health related and normal day-to-day activities; these data were entered into a geographic information system for analysis. PRINCIPAL FINDINGS: Several geographic and spatial behavior factors, including having a driver's license, use of provided rides, and distance for regular care, were significantly related to health care utilization for regular check-up and chronic care in the bivariate analysis. In the multivariate model, having a driver's license and distance for regular care remained significant, as did several predisposing (age, gender, ethnicity), enabling (household income), and need (physical and mental health measures, number of conditions). Geographic measures, as predisposing and enabling factors, were related to regular check-up and chronic care, but not to acute care visits. CONCLUSIONS: These results show the importance of geographic and spatial behavior factors in rural health care utilization. They also indicate continuing inequity in rural health care utilization that must be addressed in public policy.

Adult↗
PubMed2006

Using probability vs. nonprobability sampling to identify hard-to-access participants for health-related research: costs and contrasts.

This article compares the recruitment costs and participant characteristics associated with the use of probability and nonprobability sampling strategies in a longitudinal study of older hemodialysis patients and their spouses. Contrasts were made of people who accrued to the study based on probability and nonprobability sampling strategies. Probability-based sampling was more time-efficient and cost-effective than nonprobability sampling. There were no significant differences between the respondents identified through probability and nonprobability sampling on age, gender, years married, education, work status, and professional job status. Respondents from the probability sample were more likely to be Protestant and less likely to be Catholic than those from the nonprobability sample. Respondents from the probability sample were more likely to be Black, whereas those from the nonprobability sample were more likely to be White. There are strengths and shortcomings associated with both nonprobability and probability sampling. Researchers need to consider representativeness and external validity issues when designing sampling and related recruitment plans for health-related research.

Aged↗
PubMed2004

Treatment decision-making and the form of risk communication: results of a factorial survey.

BACKGROUND: Prospective users of preventive therapies often must evaluate complex information about therapeutic risks and benefits. The purpose of this study was to evaluate the effect of relative and absolute risk information on patient decision-making in scenarios typical of health information for patients. METHODS: Factorial experiments within a telephone survey of the Michigan adult, non-institutionalized, English-speaking population. Average interview lasted 23 minutes. Subjects and sample design: 952 randomly selected adults within a random-digit dial sample of Michigan households. Completion rate was 54.3%. RESULTS: When presented hypothetical information regarding additional risks of breast cancer from a medication to prevent a bone disease, respondents reduced their willingness to recommend a female friend take the medication compared to the baseline rate (66.8% = yes). The decrease was significantly greater with relative risk information. Additional benefit information regarding preventing heart disease from the medication increased willingness to recommend the medication to a female friend relative to the baseline scenario, but did not differ between absolute and relative risk formats. When information about both increased risk of breast cancer and reduced risk of heart disease were provided, typical respondents appeared to make rational decisions consistent with Expected Utility Theory, but the information presentation format affected choices. Those 11% - 33% making decisions contrary to the medical indications were more likely to be Hispanic, older, more educated, smokers, and to have children in the home. CONCLUSIONS: In scenarios typical of health risk information, relative risk information led respondents to make non-normative decisions that were "corrected" when the frame used absolute risk information. This population sample made generally rational decisions when presented with absolute risk information, even in the context of a telephone interview requiring remembering rates given. The lack of effect of gender and race suggests that a standard strategy of presenting absolute risk information may improve patient decision-making.

Adult↗
PubMed1995

Do some types of alcoholic beverages lead to more problems for adolescents?

OBJECTIVE: In surveys of alcohol use the alcoholic beverage preferred is sometimes noted but rarely given much attention. What little research exists on how beverage type relates to alcohol problems, delinquency and drug use has produced inconsistent results. This study identifies groups of high school students who drink beer, wine or spirits exclusively as well as those who drink multiple beverage types and examines whether problems are limited to a beverage type or a combination of types. METHOD: This study uses data from the 1991 Ontario Student Drug Use Survey. The sampling design employs a stratified (grade by region) single-stage cluster sample of homeroom classes. Students who drank alcohol at least once a month are included (N = 1,557). RESULTS: Most students (82%) drink a combination of beer, wine and spirits. However, drinker type is not related to alcohol problems, drinking and driving, tobacco use, cannabis use or drug problems, holding constant age, gender and alcohol consumption. Only for heavy drinking and delinquency is there a significant association with drinker type. Exclusive beer and spirits drinkers and drinkers of all three beverages are more likely than the other drinker types to consume five or more drinks on a single occasion and to engage in delinquent behavior. CONCLUSIONS: Drinkers of beer and spirits and all three beverage types are not only heavier drinkers but probably more rebellious and deviant. Wine, if taken exclusively, appears to be the beverage of moderation.

Accidents, Traffic↗
PubMed2006

Clinical significance of chemokine receptor (CCR1, CCR2 and CXCR4) expression in human myeloma cells: the association with disease activity and survival.

BACKGROUND AND OBJECTIVES: The capacity of multiple myeloma (MM) cells to home to and reside in the bone marrow implies that they must be equipped with appropriate adhesion molecules and chemokine receptors to allow transendothelial migration. We and others have previously shown that human MM cells express at least three different chemokine receptors that are functionally involved in MM cell migration, i.e. CCR1, CCR2 and CXCR4. In this study, we analyzed the surface expression of these chemokine receptors on primary MM cells from bone marrow samples. DESIGN AND METHODS: Chemokine receptor expression was analyzed on bone marrow samples from a large population of patients (n=80) by flow cytometric analysis. The chemokine receptor expression profile was compared with clinical characteristics. Statistical significance was evaluated by Fisher's exact test. Survival curves were constructed using the Kaplan-Meier method. Cox regression analysis was used to determine the effect of chemokine receptor expression on survival. RESULTS: A heterogeneous expression pattern was observed for the three receptors tested. The chemokine receptor status (CRS) (i.e. no expression versus expression of at least one chemokine receptor), as well as expression of individual chemokine receptors was analyzed in relation to clinical and laboratory features and evaluated for prognostic significance. Chemokine receptor expression was significantly inversely correlated with disease activity: patients with active disease showed a significantly lower expression of CCR1, CCR2, as well as CXCR4 as compared to patients with non-active disease. Furthermore, the chemokine receptor expression profile correlated with serum beta2-microglobulin, C-reactive protein and hemoglobin. CRS, and the individual expressions of CCR1, CCR2 and CXCR4 in diagnostic bone marrow samples (n=70) correlated with survival. Multivariate analysis, using the Cox proportional hazard regression model, identified CRS, along with serum beta-microglobulin, as an independent prognostic factor. INTERPRETATION AND CONCLUSIONS: This study indicates that the chemokine receptor expression profile of MM cells correlates with disease status and survival of MM patients. This observation might reflect impaired chemoattraction and retention of MM cells within the bone marrow microenvironment, resulting in disease progression.

Adult↗
PubMed2000

Designing serological surveillance programmes to document freedom from disease with special reference to exotic viral diseases of pigs in Denmark.

Surveillance programmes based on laboratory screening tests are increasingly used to document freedom from disease in order to facilitate trade. The following aspects must be considered when designing such programmes: diseases to be selected; epidemiology of the diseases; unit of analysis (animal or herd); target age group (or target farm type); test characteristics and sample size. Issues related to these aspects are discussed and illustrated using the example of serological surveillance for exotic viral diseases in the pig population of Denmark. Sampling designs based on individual animal samples are compared with herd-based sampling (two-stage sampling). While the latter is likely to require a larger sample size, the increased level of information and the reliability of the results obtained are considered to be worth the expense. Issues related to the development of international standards for declaring freedom from disease are discussed. The authors conclude that international standards are desirable, providing that these standards represent scientifically valid principles.

Age Factors↗
PubMed2001

Conditional logistic analysis of case-control studies with complex sampling.

Methods for the analysis of unmatched case-control data based on a finite population sampling model are developed. Under this model, and the prospective logistic model for disease probabilities, a likelihood for case-control data that accommodates very general sampling of controls is derived. This likelihood has the form of a weighted conditional logistic likelihood. The flexibility of the methods is illustrated by providing a number of control sampling designs and a general scheme for their analyses. These include frequency matching, counter-matching, case-base, randomized recruitment, and quota sampling. A study of risk factors for childhood asthma illustrates an application of the counter-matching design. Some asymptotic efficiency results are presented and computational methods discussed. Further, it is shown that a 'marginal' likelihood provides a link to unconditional logistic methods. The methods are examined in a simulation study that compares frequency and counter-matching using conditional and unconditional logistic analyses and indicate that the conditional logistic likelihood has superior efficiency. Extensions that accommodate sampling of cases and multistage designs are presented. Finally, we compare the analysis methods presented here to other approaches, compare counter-matching and two-stage designs, and suggest areas for further research.To whom correspondence should be addressed.

Journal Article↗
PubMed2005

Gender differences in the association between substance use and elevated depressive symptoms in a general adolescent population.

AIMS: This study explores gender differences in the association between substance use and elevated depressive symptoms in the general adolescent population. DESIGN: Cross-sectional self-reported anonymous survey, the 2002/2003 Student Drug Use Survey in the Atlantic Provinces. The sample design was a single-stage cluster sample of randomly selected classes stratified by grade and region. SETTING: The four Atlantic provinces of Canada. PARTICIPANTS: A total of 12 771 students in junior and senior high schools of the public school systems, representing a response rate of about 97%. The average age of participants was 15.2 years. MEASUREMENTS: The measure of elevated depressive symptoms was a 12-item version of the CES-D with three categories of depression risk validated in a companion study. FINDINGS: The prevalence of very elevated depressive symptoms was 8.6% in females and 2.6% in males. Alcohol use and cigarette smoking were found to be independent predictors of elevated depressive symptoms in females, but not males; cannabis use was found to be an independent predictor of elevated depressive symptoms in both males and females. Age was found to have a curvilinear relationship with elevated depressive symptoms in females but not in males. The adolescent's academic performance and province of residence were found to be independent risk factors of elevated depressive symptoms among both males and females. About 10.3% of adolescents considered to be potential candidates for needing help reported having received help because they felt depressed. CONCLUSIONS: The association between depression risk and age, alcohol use, cigarette smoking and cannabis use in the general adolescent population is not straightforward and may differ according to gender. There is unmet need for help for depression among adolescents.

Adolescent↗
PubMed2005

Dementia subtypes in China: prevalence in Beijing, Xian, Shanghai, and Chengdu.

BACKGROUND: Prevalences of Alzheimer disease (AD) and vascular dementia (VaD) in China reportedly differ from those in Western countries. OBJECTIVE: To estimate prevalence of AD and VaD in 4 regions of China. DESIGN: Cross-sectional, population-based prevalence survey with a stratified, multistage cluster sampling design. SETTING: Rural (n = 99) and urbanized (n = 71) communities of Beijing, Xian, Shanghai, and Chengdu. PARTICIPANTS: A sample of 34 807 community residents (94% of those eligible) 55 years or older. MAIN OUTCOME MEASURES: Participants were screened with the Chinese Mini-Mental State Examination. Those who screened positive (n = 3950) underwent a standardized diagnostic workup. Screening sensitivity was assessed in a 3.3% random sample (n = 1008 of the 30 857 who passed the screening). Diagnoses of AD and VaD were made according to National Institute of Neurological and Communicative Diseases and Stroke-Alzheimer Disease and Related Disorders Association and National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences criteria, respectively. Final diagnoses were made after a 6-month confirmation interval. RESULTS: We identified 732 AD cases and 295 VaD cases. Prevalence in persons 65 years or older was 3.5% (95% confidence interval, 3.0%-3.9%) for AD and 1.1% (95% confidence interval, 0.9%-1.1%) for VaD. After post hoc correction for negative screening errors, prevalence increased to 4.8% for AD and remained at 1.1% for VaD. CONCLUSION: Prevalence of dementia subtypes in China is comparable with that in Western countries.

Aged↗
PubMed1997

The OBRA-87 nursing home regulations and implementation of the Resident Assessment Instrument: effects on process quality.

OBJECTIVE: To characterize changes in key aspects of process quality received by nursing home residents before and after the implementation of the national nursing home Resident Assessment Instrument (RAI) and other aspects of the Omnibus Budget Reconciliation Act (OBRA) nursing home reforms. DESIGN: A quasi-experimental study using a complex, multistage probability-based sample design, with data collected before (1990) and after (1993) implementation of the RAI and other OBRA provisions. SETTING AND PARTICIPANTS: Two independent cohorts (n > 2000) of residents in a random sample of 254 nursing facilities located in metropolitan statistical areas in 10 states. INTERVENTION: OBRA-87 enhanced the regulation of nursing homes and included new requirements on quality of care, resident assessment, care planning, and the use of neuroleptic drugs and physical restraints. One of the key provisions, used to help implement the OBRA requirements in daily nursing home practice, was the mandatory use of a standardized, comprehensive system, known as the RAI, to assist in assessment and care planning. OBRA provisions went into effect in federal law on October 1, 1990, although delays issuing the regulations led to actual implementation of the RAI during the Spring of 1991. MEASUREMENTS AND ANALYSES: Research nurses spent an average of 4 days per facility in each data collection round, assessing a sample of residents, collecting data through interviews with and observations of residents, interviews with multiple shifts of direct staff caregivers for the sampled residents, and review of medical records, including physician's orders, treatment and care plans, nursing progress notes, and medication records. The RNs collected data on the characteristics of the sampled residents, on the care they received, and on facility practices. The effect of being a member of the 1990 pre-OBRA or the 1993 post-OBRA cohort was assessed on the accuracy of information in the residents' medical records, the comprehensiveness of care plans, and on other key aspects of process quality while controlling for any changes in resident case-mix. The data were analyzed using contingency tables and logistic regression and a special statistical software (SUDAAN) to assure proper variance estimation. RESULTS: Overall, the process of care in nursing homes improved in several important areas. The accuracy of information in residents' medical records increased substantially, as did the comprehensiveness of care plans. In addition, several problematic care practices declined during this period, including use of physical restraints (37.4 to 28.1% (P < .001)) and indwelling urinary catheters (9.8 to 7% (P < .001)). There were also increases in good care practices, such as the presence of advanced directives, participation in activities, and use of toileting programs for residents with bowel incontinence. These results were sustained after controlling for differences in the resident characteristics between 1990 and 1993. Other practices, such as use of antipsychotic drugs, behavior management programs, preventive skin care, and provision of therapies were unaffected, or the differences were not statistically significant, after adjusting for changes in resident case-mix. CONCLUSION: The OBRA reforms and introduction of the RAI constituted an unprecedented implementation of comprehensive geriatric assessment in Medicare- and Medicaid-certified nursing homes. The evaluation of the effects of these interventions demonstrates significant improvements in the quality of care provided to residents. At the same time, these findings suggest that more needs to be done to improve process quality. The results suggest the RAI is one tool that facility staff, therapists, pharmacy consultants, and physicians can use to support their continuing efforts to provide high quality of care and life to the nation's 1.7 million nursing home residents.

Advance Directives↗
PubMed2001

Improved rapid sampling for in vivo kinetics of intracellular metabolites in Saccharomyces cerevisiae.

An integrated approach is used to develop a rapid sampling strategy for the quantitative analysis of in vivo kinetic behavior based on measured concentrations of intracellular metabolites in Saccharomyces cerevisiae. Emphasis is laid on small sample sizes during sampling and analysis. Subsecond residence times are accomplished by minimizing the dead volume of the sterile sampling system and by maximizing flow rates through application of vacuum to the sampling tubes in addition to the overpressure in the fermenter. A specially designed sample tube adapter facilitates sampling intervals of 4 to 5 s for various test tube types. Statistical analysis of the results obtained from enzymatic and liquid chromatography mass spectrometry (LC-MSMS) analysis of the metabolite concentrations was used to optimize the sampling protocol. The most notable improvement is reached through the introduction of vacuum drying of the cell extract. The presented system is capable of reliably dealing with fermenter samples as small as 1-g with a variation of less than 3%, and is thus ideally suited for intracellular measurements on small, lab-scale fermenters.

Biomass↗
PubMed1994

Cigarette smoking in the U.S. military: findings from the 1992 Worldwide Survey.

BACKGROUND: Using data from the military's Worldwide Survey series, this article presents findings on the prevalence of smoking among active-duty military personnel in 1992 and trends since 1980. METHODS: A stratified probability sampling design was used in the 1992 Worldwide Survey. Military installations worldwide were sampled, and then active-duty personnel within these installations were selected. A total of 16,395 usable questionnaires were obtained, for an overall response rate of 77.3%. RESULTS: The prevalence of cigarette smoking among military personnel has declined from 51% in 1980 to 35% in 1992. This decline was not explained by changes in the sociodemographic composition of the military population. Overall, smoking was more prevalent among personnel who were white, had less education, and were enlisted. In addition, enlisted men reporting higher levels of work-related stress were more likely to be smokers. Over half of all military personnel who were smokers in the past year attempted to quit. CONCLUSIONS: The military has made considerable progress since 1980 in reducing the prevalence of smoking among military personnel. Nonetheless, the prevalence in 1992 was still relatively high, affecting about one of every three personnel. A promising group to target in future antismoking efforts may be smokers who tried to quit during the past year.

Adult↗
PubMed1999

Measures of spatial structure in samples of genotypes for multiallelic loci.

Various spatial autocorrelation statistics have been widely used both in theoretical population genetics and to study the spatial distribution of diploid genotypes in many plant and animal populations. However, previous simulation studies have considered only diallelic loci. In this paper, we use a large number of space-time simulations to characterize for the first time the parametric and statistical values of Moran's I-statistics for converted individual genotypes as well as for join-count statistics. A wide range of levels of dispersal and numbers of alleles and allele frequencies are modelled and the results reveal the different general effects of each of these factors on these statistics. We also examine the range of appropriate sampling designs and sizes for which predicted values can be interpolated for specific sampling schemes for any given population genetic field survey. Numbers of alleles and allele frequencies each affect some statistics but not others. The results indicate generally low standard deviations. The results also develop precise and efficient methods of estimating gene dispersal, based on the various autocorrelation measures of standing spatial patterns of genetic variation within populations. The results also extend these methods to loci with multiple alleles, typical of those studied through modern molecular methods.

Alleles↗
PubMed1998

Does the ethnicity of teenage children influence oral self perception and prevalence of dental disease?

AIM: The primary aim was to evaluate the effect of ethnicity, social deprivation and oral health on oral self perceptions of 14-15-year-old Asians and Whites. A secondary aim was to assess the influence of ethnicity and social deprivation on oral treatment need in the same sample. DESIGN: A cross-sectional epidemiological study. DATA SOURCE: A stratified, random sample of 408 14-15-year-old Asian and White children from schools in Manchester. METHOD: Information was collected on oral self perceptions using a questionnaire and on oral treatment need with a clinical examination. RESULTS: Multivariate data analysis revealed that oral treatment need, but not ethnicity or social deprivation, was an important predictive variable with respect to oral self perceptions. Ethnicity was the only variable to influence periodontal treatment need. Social deprivation influenced the level of untreated caries. CONCLUSIONS: 1. Socially deprived children have higher caries levels than their more affluent counterparts and this is evident regardless of ethnic background. 2. Although Asian 14-15-year-old children have a higher periodontal treatment need than Whites, there was no ethnic influence on how they perceive their oral health. 3. Oral treatment need is an important factor with respect to oral self perceptions.

Adolescent↗