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PubMed1995

Predictors of Pap smear screening in socioeconomically disadvantaged elderly women.

OBJECTIVE: The objective for this study was to identify predictors for participation in Pap smear screening in a socioeconomically disadvantaged older population. DESIGN AND SAMPLE: A cross-sectional survey design was used to examine data from 238 southern women 50 years of age and older who were recruited from 24 randomly selected congregate meal sites of the Council on Aging. MEASUREMENTS: The 45-item questionnaire covered demographics, Pap smear screening history, and colorectal cancer screening history. RESULTS: Among this older, very low income population, women who had never had Pap smears (17.2%) were significantly more likely to have no phone or to be unable to use a phone (adjusted odds ratio (aOR) = 4.1; 95% confidence interval (CI) 1.6-10.6), to have annual incomes of less than $5,800 (aOR = 3.1; 95% CI 1.1-9.0), to be widowed (aOR = 2.8; 95% CI 1.1-7.3), to have no family history of cancer (aOR = 3.3, 95% CI 1.3-10.0), to report having never had a rectal examination (aOR = 5.4, 95% CI 1.8-16.0), and not to have participated in a free fecal occult blood testing program (aOR = 5.0, 95% CI 2.0-10.0). CONCLUSIONS: These data, unique in including very low income (< $10,000) and older women (65 and over), found that income and access to a phone were strongly correlated with cervical cancer screening participation. Women who lacked external incentives for screening (being widowed and not having a family history of cancer) were less likely to obtain screening. This study's finding that "not having a phone" was a strong predictor for nonparticipation in cervical cancer screening has implications for national telephone-derived estimates of cervical cancer screening.

Age Factors↗
PubMedDate not supplied

The effect of data sampling on the performance evaluation of artificial neural networks in medical diagnosis.

PURPOSE: To study the effect of data sampling on the predictive assessment of artificial neural networks (ANNs) for medical diagnostic tasks. METHODS: Three statistical techniques were used to evaluate the diagnostic performances of ANNs: 1) cross validation, 2) round robin, and 3) bootstrap. These techniques are different sampling plans designed to reduce the small-sample estimation bias and variance contributions. The study was based on two networks, one developed for the diagnosis of pulmonary embolism (1,064 cases) and the other developed for the diagnosis of breast cancer (206 cases). RESULTS: The three sampling techniques produced different performance estimates for both networks. The estimates varied substantially depending on the training sample size and the training-stopping criterion. CONCLUSION: The predictive assessment of ANNs in medical diagnosis can vary substantially based on the complexity of the problem, the data sampling technique, and the number of cases available.

Breast Neoplasms↗
PubMed2004

Observed intra-cluster correlation coefficients in a cluster survey sample of patient encounters in general practice in Australia.

BACKGROUND: Cluster sample study designs are cost effective, however cluster samples violate the simple random sample assumption of independence of observations. Failure to account for the intra-cluster correlation of observations when sampling through clusters may lead to an under-powered study. Researchers therefore need estimates of intra-cluster correlation for a range of outcomes to calculate sample size. We report intra-cluster correlation coefficients observed within a large-scale cross-sectional study of general practice in Australia, where the general practitioner (GP) was the primary sampling unit and the patient encounter was the unit of inference. METHODS: Each year the Bettering the Evaluation and Care of Health (BEACH) study recruits a random sample of approximately 1,000 GPs across Australia. Each GP completes details of 100 consecutive patient encounters. Intra-cluster correlation coefficients were estimated for patient demographics, morbidity managed and treatments received. Intra-cluster correlation coefficients were estimated for descriptive outcomes and for associations between outcomes and predictors and were compared across two independent samples of GPs drawn three years apart. RESULTS: Between April 1999 and March 2000, a random sample of 1,047 Australian general practitioners recorded details of 104,700 patient encounters. Intra-cluster correlation coefficients for patient demographics ranged from 0.055 for patient sex to 0.451 for language spoken at home. Intra-cluster correlations for morbidity variables ranged from 0.005 for the management of eye problems to 0.059 for management of psychological problems. Intra-cluster correlation for the association between two variables was smaller than the descriptive intra-cluster correlation of each variable. When compared with the April 2002 to March 2003 sample (1,008 GPs) the estimated intra-cluster correlation coefficients were found to be consistent across samples. CONCLUSIONS: The demonstrated precision and reliability of the estimated intra-cluster correlations indicate that these coefficients will be useful for calculating sample sizes in future general practice surveys that use the GP as the primary sampling unit.

Australia↗
PubMed2001

Body mass index: comparing mean values and prevalence rates from telephone and examination surveys.

BACKGROUND: Cost effective means of assessing the levels of risk factors in the population have to be defined in order to monitor these factors over time and across populations. This study is aimed at analyzing the difference in population estimates of the mean levels of body mass index (BMI) and the prevalences of overweight, between health examination survey and telephone survey. METHODS: The study compares the results of two health surveys, one by telephone (N=820) and the other by physical examination (N=1318). The two surveys, based on independent random samples of the population, were carried out over the same period (1992-1993) in the same population (canton of Vaud, Switzerland). RESULTS: Overall participation rates were 67% and 53% for the health interview survey (HIS) and the health examination survey (HES) respectively. In the HIS, the reporting rate was over 98% for weight and height values. Self-reported weight was on average lower than measured weight, by 2.2 kg in men and 3.5 kg in women, while self-reported height was on average greater than measured height, by 1.2 cm in men and 1.9 cm in women. As a result, in comparison to HES, HIS led to substantially lower mean levels of BMI, and to a reduction of the prevalence rates of obesity (BMI>30 kg/m(2)) by more than a half. These differences are larger for women than for men. CONCLUSION: The two surveys were based on different sampling procedures. However, this difference in design is unlikely to explain the systematic bias observed between self-reported and measured values for height and weight. This bias entails the overall validity of BMI assessment from telephone surveys.

Adult↗
PubMed2004

HIV/AIDS prevalence among South African health workers.

INTRODUCTION: Studies on HIV prevalence among health workers usually focus on occupational exposure to HIV. Little is known about HIV prevalence in this group. However, it is expected that HIV prevalence among health workers will reflect prevalence in their society. OBJECTIVE: To determine HIV prevalence among South African health workers. METHOD: A stratified cluster sample was drawn of 5% of health facilities in South Africa (N = 222) representative of the public and private health sectors in South Africa. The sample was designed to obtain a nationwide representative sample of medical professionals and non-professional health workers. A subsample comprising health workers in four provinces was tested for HIV status. The Orasure HIV-1 device in combination with the Vironostika HIV UNI-Form II plus O enzyme-linked immunosorbent assay (ELISA) kits were used to collect oral fluid specimens for HIV testing. RESULTS: Based on a sample of 721 health workers and a response rate of 82.5% (or 595 respondents), the study found that an estimated 15.7% (95% confidence interval (CI): 12.2-19.9%) of health workers employed in the public and private health facilities located in four South African provinces, were living with HIV/AIDS in 2002. Among younger health workers, the risk is much higher. This group (aged 18-35 years) had an estimated HIV prevalence of 20% (95% CI: 14.1-27.6%). Non-professionals had an HIV prevalence of 20.3%, while professionals had a prevalence of 13.7%. CONCLUSION: HIV prevalence among health workers in South Africa is high; this calls for the introduction of antiretroviral programmes targeting them. In addition, there is a need for the development of new policy regarding placement of infected health workers in tuberculosis (TB) wards, coupled with vigorous human resource planning to replace the health workers likely to die from AIDS. Infection control procedures also need to be reviewed.

Adult↗
PubMedDate not supplied

View of the International Dairy Federation on interlaboratory analytical studies.

The International Dairy Federation develops and studies methods for the analysis of milk and milk products. A first draft of an IDF protocol for conducting interlaboratory studies is presented. Major features of the protocol are type and number of participating laboratories; nature, duplication, and number of sample materials; final design (numbers of samples and laboratories); statistical analysis of the data; report of the final results.

Dairy Products↗
PubMed2003

Sampling patients within physician practices and health plans: multistage cluster samples in health services research.

OBJECTIVE: To better inform study design decisions when sampling patients within health plans and physician practices with multiple analysis goals. STUDY SETTING: Chronic eye care patients within six health plans across the United States. STUDY DESIGN: We developed a simulation-based approach for designing multistage samples. We created a range of candidate designs, evaluated them with respect to multiple sampling goals, investigated their tradeoffs, and identified the design that is the best compromise among all goals. This approach recognizes that most data collection efforts have multiple competing goals. DATA COLLECTION: We constructed a sample frame from all diabetic patients in six health plans with evidence of chronic eye disease (glaucoma and retinopathy). PRINCIPAL FINDINGS: Simulations of different study designs can uncover efficiency gains as well as inform potential tradeoffs among study goals. Simulations enable us to quantify these efficiency gains and to draw tradeoff curves. CONCLUSIONS: When designing a complex multistage sample it is desirable to explore the tradeoffs between competing sampling goals via simulation. Simulations enable us to investigate a larger number of candidate designs and are therefore likely to identify more efficient designs.

Cluster Analysis↗
PubMed2006

Design and stabilization of sampled-data neural-network-based control systems.

This paper presents the design and stability analysis of a sampled-data neural-network-based control system. A continuous-time nonlinear plant and a sampled-data three-layer fully connected feedforward neural-network-based controller are connected in a closed loop to perform the control task. Stability conditions will be derived to guarantee the closed-loop system stability. Linear-matrix-inequality- and genetic-algorithm-based approaches will be employed to obtain the largest sampling period and the connection weights of the neural network subject to the considerations of the system stability and performance. An application example will be given to illustrate the design procedure and effectiveness of the proposed approach.

Algorithms↗
PubMed1997

Logistics and design issues in the use of biological samples in observational epidemiology.

Standard epidemiological study designs are well suited to answering questions involving the collection of biological samples. However, different designs are better suited--both for design and logistic reasons--to different questions. The strengths and weaknesses of each design are discussed in relation to markers of exposure, susceptibility and early outcome, and to markers used to classify cancers into biologically defined subsets.

Animals↗
PubMed1999

Ethics and practice: alternative designs for phase III randomized clinical trials.

For decades, biostatisticians have developed and refined the methodology for clinical trials with the intent of giving trial participants a better representation than traditional, equal-allocation, fixed sample-size designs. Despite these methodologic advances and ethical advantages, alternative or data-dependent designs for phase III clinical trials, including sequential designs, Bayesian methods, and adaptive designs, have not been widely adopted in practice. We attempt to characterize situations under which these designs are feasible and desirable from ethical and logistical standpoints. In particular, we describe the role of individual and collective ethics in designing clinical trials and argue that greater attention should be paid to the former. We give examples of those alternative designs that have been used in practice, including discussion of their strengths and shortcomings. We conclude that alternative designs are applicable in limited classes of trials and that investigators should consider them more often when planning clinical trials.

Bayes Theorem↗
PubMed1992

The epidemiology of genetic epidemiology.

Familial aggregation for disease is important; strong familial risk factors must exist even if the increased risk to a relative of an affected individual is modest. It is in practice difficult, however, to conduct studies in genetic epidemiology which conform to strict epidemiological principles. For twin studies there are two major questions: Are twins 'no different' from the population on which inference is to be made? Are study twins 'no different' to twins in the population? The importance of each question of bias depends on the scientific question, the trait(s) studied, and sampling issues. The strength of the twin design is its ability to refute the null hypothesis that genetic factors do not explain variation in a trait. Following the Popperian paradigm, alternate hypotheses should be considered in depth (both theoretically and empirically), with a design and sample size sufficient to exclude not just naive explanations. More sophisticated statistical techniques are now being applied, so the philosophy, assumptions, and limitations of statistical modelling must be appreciated. The concept of 'heritability' has, in the past, been misunderstood and misused. New advances in DNA technology promise to revolutionise epidemiological thinking, and so case-control-pedigree designs may well become standard tools. The strengths and limitations of studies based on related individuals as the sampling unit are discussed.

Adult↗
PubMed1997

Black-white differences in body size perceptions and weight management practices among adolescent females.

OBJECTIVE: This study compares body size perceptions and weight management practices of black and white adolescent females. DESIGN: Subjects were selected through a statewide, three-stage sampling procedure designed to provide a sample statistically representative of high school students in South Carolina. SUBJECTS: Participants included black (n = 1824) and white (n = 2256) females, 14-18 years of age, enrolled in South Carolina public high schools. METHODS: Respondents were asked to assess their perceived body size as overweight, underweight, or about right. Self-reported weight management practices included dieting (reducing caloric intake), exercise, and other methods (including diet pills and vomiting). Chisquare analysis was used to assess the differences in body size perception and weight management behaviors. Polychotomous logistic regression was performed to examine association while controlling for socioeconomic status. RESULTS: Forty-one percent of the white adolescents and 29% of the black adolescents perceive themselves as overweight (p < 0.005). In the week prior to the survey, 28% of the white adolescents and 13% of the black adolescents reported dieting 34% of the while versus 23% of the black adolescents reported exercising to lose weight; and 45% of the white and 16% of the black students reported both dieting and exercising. Polychotomous logistic regression analysis showed that white adolescent girls were almost twice as likely to perceive themselves as overweight as black adolescent girls. The white students had 6.04 [95% confidence interval (CI), 1.77, 20.67] times the odds of using pills and vomiting and 3.76 (95% CI, 2.99, 4.72) times the odds of engaging in dieting and exercising as methods of weight management compared to the black students. CONCLUSIONS: These findings suggest that white adolescents are more likely to perceive themselves as overweight than black adolescents and are more likely to engage in unhealthy weight management practices than black adolescents.

Adolescent↗
PubMed2001

Study sampling in the Canadian Study of Health and Aging.

The Canadian Study of Health and Aging drew representative samples of people aged 65 or over from the community and institutions across Canada. The sample was designed to provide regional and national prevalence estimates for dementia by age and sex. Thirty-six sampling areas were used in a stratified cluster design with optimal allocation; sampling weights were developed to provide population estimates. The sample included 9,008 people aged 65 or over from the community, and 1,255 from institutions. This report describes the sampling procedures, the methods used to recruit people to the study and participation rates, the characteristics of the resulting sample, and the way in which sample weights should be used.

Aged↗
PubMed1981

Sampling methods for pharmacokinetic studies in the mouse.

Pharmacokinetics data on 2,4,5-T are used to illustrate design considerations, agent administration and sampling techniques required for single-animals studies in mice. Detailed methods for intravenous and intragastric delivery of chemicals are described, as are small volume (3 microliters) blood sampling techniques from tail vein and orbital plexus. A mouse metabolism cage is described that prohibits feed contamination of urine and feces, and also effectively segregates these elimination products. Techniques for blood, urine, and feces sample preparation and quality control assessments are also presented. Multi-sample blood concentration-time curves obtained from a single mouse are compared to data obtained using a single-sample design using may mice. While a single-animal, multiple-sample design requires the availability of microanalytical methods, it has many economic and practical advantages and results in a more accurate pharmacokinetic profile of the chemical in mice.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed2006

Effect of personal and cultural beliefs on medication adherence in the elderly.

Approximately 50% of patients across all age groups with varied types of medical conditions do not adhere to their prescribed medication regimens. Medication nonadherence is common in older adults who are often prescribed medications for age-related chronic disorders. The purpose of this paper is to investigate the effect of personal and cultural beliefs on older adults' medication adherence through a review of research studies published in journals across different disciplines. A systematic literature search using ten databases found 14 articles meeting the inclusion criteria. Belief-laden variables including self-efficacy (i.e. the belief that one can perform a specific behaviour under differing conditions), medication efficacy, confidence in the physician's knowledge, perceptions about natural products and home remedies, beliefs of control (over one's health), and illness perceptions were found to be significantly related to medication adherence among older adults. However, several measurement, design and sampling problems were identified in this review. The majority of the studies in the review evaluated older adults' medication adherence by self-report and used cross-sectional designs and convenience samples. Future studies should utilise prospective longitudinal designs and a more objective measure of medication adherence, such as electronic event monitoring, when examining factors related to older adults' medication adherence. Future research should also evaluate belief-related variables in larger and more ethnically diverse samples of older adults. Implications for assessment and intervention are evident from this literature review of the effect of personal and cultural beliefs on medication adherence in older adults.

Aged↗
PubMed1996

[Analysis of the block design test in a geriatric sample group].

We have carried out a study to determine the normal values of the 'block design test' in a sample group of 58 healthy elderly persons, a test which is usually used in the clinical evaluation of constructive apraxia. We therefore describe a grading scale which has not been previously published, in order to check the possible usefulness of this drawing as a rapid test of cognitive evaluation. A study was made of the possible interaction of the test with sample parameters, age, sex, educational level and also the inter-examiner reliability. We have observed a significant interaction between the variables of sex and educational level. Also the inter-examiner reliability is not very good. In view of our results, we consider that the 'block design test' is not very useful in the evaluation of constructive praxis in healthy elderly persons, and therefore it does not seem to us to be a good test for the rapid evaluation of cognitive function in this group.

Aged↗
PubMed2004

Respondent-driven sampling to recruit MDMA users: a methodological assessment.

Recruiting samples that are more representative of illicit drug users is an on-going challenge in substance abuse research. Respondent-driven sampling (RDS), a new form of chain-referral sampling, is designed to eliminate the bias caused by the non-random selection of the initial recruits and reduce other sources of bias (e.g. bias due to volunteerism and masking) that are usually associated with regular chain-referral sampling. This study provides a methodological assessment of the application of RDS among young adult MDMA/ecstasy users in Ohio. The results show that the sample compositions converged to equilibrium within a limited number of recruitment waves, independent of the characteristics of the initial recruits (i.e. seeds). The sample compositions approximated the theoretical equilibrium compositions, and were not significantly different from the estimated population compositions-with the exception that White respondents were over-sampled and Black respondents were under-sampled. The effect of volunteerism and masking on the sampling process was found not to be significant. Though identifying productive seeds and improving the referral rate are significant challenges when implementing RDS, the findings demonstrate that RDS is a flexible and robust sampling method. RDS has the potential to be widely employed in studies of illicit drug-using populations.

Epidemiologic Research Design↗