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Results for “Sample size estimation”

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At least 523 records · Page 29Linked to original sources
PubMed1989

Preventing osteoporosis with exercise: a review with emphasis on methodology.

Exercise is thought to have considerable potential as a preventive for osteoporosis. We critically examined 27 studies that address the prophylactic role of exercise in osteoporosis. The results from both cross-sectional and longitudinal studies showed that differences in bone mass were more pronounced in the axial skeleton as opposed to the peripheral compact skeleton. The 17 cross-sectional studies demonstrated greater bone mass among highly trained athletes compared with sedentary subjects, while results among recreational athletes were inconsistent. The 10 prospective investigations examining the effect of exercise on bone mass yielded conflicting results; only one study of six found an overall positive response in compact bone mass at the radial site, and only one study examining the spine showed a significant gain among the exercisers. Additionally, all the prospective investigations included serious methodologic flaws; most failed to employ a randomized design, appropriate estimates of sample size were lacking, none provided information on blind outcome assessment, and most studies were of short duration. Current evidence suggests that exercise may have only limited value in affecting bone mass in the short term and widespread recommendations for the prophylactic use of exercise should await further validation using better methodological rigor.

Bone and Bones↗
PubMedDate not supplied

Neurobehavioral Evaluation System (NES): comparative performance of 2nd-, 4th-, and 8th-grade Czech children.

The Neurobehavioral Evaluation System was designed for field studies of workers, but many NES tests can be performed satisfactorily by children as young as 7 or 8 years old and a few tests, such as simple reaction time, can be performed by preschool children. However, little comparative data from children of different ages or grade levels are available. Studies of school children in the Czech Republic indicate that 2nd-grade children could perform the following NES tests satisfactorily: Finger Tapping, Visual Digit Span. Continuous Performance, Symbol-Digit Substitution, Pattern Comparison, and simpler conditions of Switching Attention. Comparative scores of boys and girls from the 2nd, 4th, and 8th grades and power analyses to estimate appropriate sample size were presented. Performance varied systematically with grade level and gender. Larger samples were needed with younger children to achieve comparable levels of statistical power. Gender comparisons indicated that boys responded faster, but made more errors than girls.

Adolescent↗
PubMed2005

The lifestyle interventions and independence for elders (LIFE) pilot study: design and methods.

The LIFE study is a multicenter pilot for a proposed full scale, two-arm randomized controlled trial that will contrast the effect of a physical activity intervention with a successful aging education program on the occurrence of incident major mobility disability (the inability to complete a 400 m walk) or death in at-risk sedentary older adults. Four hundred older adults from 4 clinical sites will be recruited for this purpose. All participants will be followed for at least 1-year; however, we will continue to follow all participants until the final randomized individual has reached the 1-year mark. This will enable us to acquire additional information about maintenance. Additional outcomes will include lower extremity physical performance as well as gait speed over 4 m and 400 m. These latter measures will provide data on the efficacy of the intervention on intermediate endpoints linked to the primary outcome of interest. The goals of the pilot study are to (a) estimate the sample size needed for a full scale trial, (b) examine the consistency of the effects of the physical activity intervention on several continuous measures of physical function, (c) assess the feasibility of recruitment, (d) evaluate study adherence and retention, (d) evaluate the efficacy of a stepped care approach for managing intercurrent illness in this at-risk population, and (e) develop a comprehensive system for monitoring and ensuring participant safety. Other goals of this pilot phase include assessments of health-related quality of life and cost-effectiveness.

Aged↗
PubMed2000

General equations for Pt, Ps, and the power of the TDT and the affected-sib-pair test.

Several equations are highlighted here, whose algebraic symmetries and generality make them very useful for understanding and comparing the properties of the transmission disequilibrium test (TDT) and affected sib-pair test. Methods using the equations are also presented that yield precise estimates of sample sizes needed for genome scans or for testing a single candidate gene, and these power methods are shown to compare favorably with alternative approaches recently described by Knapp (1999) and by Tu and Whittemore (1999). Simple relationships are also noted that summarize the relative sample sizes required for equivalent power to detect association by the TDT or case-control designs. As single-nucleotide polymorphism (SNP) maps revolutionize the search for disease-causing genes, the equations should prove useful for planning and evaluating studies of linkage and association across a broad range of possible disease models and relationships between markers and linked disease loci.

Alleles↗
PubMed2002

Biostatistical consultation for dental research.

Dental science researchers do not really need a detailed, ready-at-hand knowledge of statistics to design and perform high quality scientific research. Although the acquisition and utilization of such knowledge by dental researchers is not discouraged, it is proposed that it is more important for dental researchers to be committed to developing and maintaining a long term, ongoing, interactive consulting relationship with a biostatistician. The nature of this relationship will depend in large part on the complexity of the dental research being conducted. While the statistical consultant will assist in interpreting analytic results for the dental researcher, the latter will need to provide extensive input in assisting in the estimation of sample size and power, and for expressing scientific hypotheses in statistical terms so that the appropriate data analytic methodology can be specified.

Analysis of Variance↗
PubMed1998

Risk of hemolytic uremic syndrome after sporadic Escherichia coli O157:H7 infection: results of a Canadian collaborative study. Investigators of the Canadian Pediatric Kidney Disease Research Center.

OBJECTIVES: The objectives of this study were to better estimate the age-specific risks of hemolytic uremic syndrome (HUS) and hemolytic anemia after Escherichia coli O157:H7 infection among a representative cohort of both referred and nonreferred children with documented illness from the province of Alberta and to compare this with the rates in children evaluated at referral centers in the rest of Canada. STUDY DESIGN: Children with HUS or E. coli O157:H7 gastroenteritis were eligible if they were < 15 years of age. Hemoglobin, blood smear, urinalysis, and serum creatinine were obtained 8 to 10 days after the onset of diarrhea to ascertain for hemolysis, anemia, thrombocytopenia, and renal injury. Subjects were monitored for 1 month. RESULTS: From June 1991 to March 1994, HUS was diagnosed in 205 children. Of these 77% had evidence of E. coli O157:H7 infection. A further 582 children had E. coli O157:H7 gastroenteritis, of whom 18 had hemolytic anemia. The risk of HUS after E. coli O157:H7 infection in Alberta was 8.1% (95% confidence interval, 5.3 to 11.6) compared with 31.4% in referral centers in the rest of Canada. In Alberta the highest age-specific risk of HUS/hemolytic anemia was 12.9% in those < 5 years of age. CONCLUSIONS: These data will help guide clinical care and provide a basis for estimating the sample sizes required in future treatment trials for the secondary prevention of HUS.

Adolescent↗
PubMed2001

A self-designing rule for clinical trials with arbitrary response variables.

For testing both one-sided and two-sided hypotheses concerning several treatment arms in group sequentially performed clinical trials with arbitrary outcome variables, a general method is considered that allows one to completely self-design a study. All information available prior to a stage is used for estimating the sample size and the weight for the next step. In "using up" the variance, the test statistic is built in a bounded finite but random number of stages to test just once the rejection of the null hypothesis. Control Clin Trials 2001;22:111-116

Clinical Trials as Topic↗
PubMed1999

Survival versus years of healthy life: which is more powerful as a study outcome?

Studies of interventions that are intended to improve patients' health are often evaluated with survival as the primary outcome, even when a measure adjusted for quality of survival, such as years of healthy life (YHL), would seem more appropriate. The purpose of this article is to determine whether studies based on survival are more or less powerful than studies based on YHL in clinical trials where either measure might be appropriate. We used data from the Cardiovascular Health Study (CHS) to estimate the sample size that would be needed in studies of 156 different health conditions, for the two outcome measures. The median sample size for a 5-year study was 687 if survival was the endpoint and 484 for YHL. YHL usually required lower sample sizes than survival, although survival was more powerful for some health conditions. We also found that lengthy studies, and studies with many follow-up measures per person, did not have appreciably higher power than less intensive studies. We conclude that clinical investigations in which the goal is to improve health may often be performed more efficiently with YHL rather than survival as the primary outcome measure. Such studies can be short in duration, with relatively few measures per person of health status.

Aged↗
PubMed2000

[Diagnostic consistency between primary care and specialized care following emergency consultation].

OBJECTIVE: To evaluate the diagnostic concordance between primary health-care level and hospital health-care level after emergency visits. DESIGN: Cross-sectional study. SETTING: Health-care area 7 in Madrid. PARTICIPANTS: Any patient studied in the primary health-care level and further sent by referral request to the emergencies of the health-care area reference hospital. MEASUREMENTS AND RESULTS: The sample size was estimated according to a confidence level of 95%, a precision level of 5%, a concordance level of 50% and a 30% of referral requests without diagnosis. All diagnosis were codified by the ICD-9 CM. Single kappa index for each diagnosis and global kappa index were calculated. 559 patients were studied. 447 (80%) of the patients were referred with diagnosis and 112 (20%) without it. Kappa index was very high (> or = 0.8) for the following diagnosis: angina pectoris, and urticaria. Kappa index was high (0.6 > or = k < 0.8) for stroke, and deep venous thrombosis. It was moderate (0.4 > or = k < 0.6) for pneumonia, heart failure and heart attack. Kappa index was low (0.2 > or = k < 0.4) for appendicitis, and arthritis, and it was very low (< 0.2) for meningitis, and cellulitis. Global kappa index was 0.65 (95% CI, 0.58-0.72). CONCLUSIONS: Global concordance was high. The highest concordance was obtained for diseases with clinical diagnosis. Most of diseases with low and very low concordance are diseases that need specialized clinical tests.

Cross-Sectional Studies↗
PubMed1999

Adjusted odds ratios under nondifferential misclassification: application to prostate cancer.

The high prevalence of unsuspected prostate cancer among middle-aged and elderly men is unique among cancers. With their uncertain natural history, unsuspected prostate cancer cases may be misclassified into control groups in which they can obscure the identification of prostate cancer risk factors in case-control studies. Assuming that the exposure experience of diagnosed and of unsuspected prostate cancers is the same (nondifferential misclassification), case-control odds ratios are biased toward the null, which may provide a rationale for reexamining findings in negative case-control studies of prostate cancer. This article reviews the evidence supporting a high prevalence of prostate cancer and describes formulae that can be used to adjust for misclassification bias in completed case-control studies and to estimate required sample sizes in proposed studies.

Adult↗
PubMed2000

Immunization coverage among predominantly Hispanic children, aged 2-3 years, in central Los Angeles.

PURPOSE: To assess the immunization status of young children in a predominantly Hispanic region in and around downtown Los Angeles, and factors associated with complete immunization by age 24 months. METHODS: The information was gathered in a two-stage cluster survey with probability proportionate to estimated size (PPS) sampling of 30 clusters at the first stage, and simple random sampling of a constant number of children at the second stage. Vaccination coverage was determined by a review of the home immunization (HI) card, or of clinic records. RESULTS: Of the 270 sampled children, 91.5% were Hispanic and 6.7% were Black. Home telephone numbers were not available in 24.8% of the homes, and 34.1% reported having no health insurance. Vaccination coverage was over 90% for the first three doses of Diphtheria, tetanus toxoids and pertussis/ diphtheria, tetanus toxoids and acellular pertussis vaccine (DTP/DTaP)/Diphtheria and tetanus toxoids vaccine (DT), first two doses of poliovirus (Polio) vaccine, first dose of measles, mumps and rubella (MMR) vaccine, and first two doses of hepatitis B (Hep B) vaccine. Yet, by age 24 months, only 72.2% of the children had received the combined series of 4:3:1 (i.e., four DTP/DTaP/DT, three Polio, one MMR). This was further reduced to 64.4% for the combined series of 4:3:1:3:3 (i.e., four DTP/DTaP/ DT, three Polio, one MMR, three Haemophilus influenzae type b (Hib), three Hep B). Factors associated with completed on-time vaccination were having an HI card available during the interview and being enrolled in Supplemental Nutrition Program for Women, Infants and Children (WIC). CONCLUSIONS: While vaccination levels for individual antigens were found to be high, more emphasis needs to be placed on getting preschool children vaccinated on-time according to the Recommended Childhood Immunization Schedule.

Child, Preschool↗
PubMed2002

Natural history of hay fever and pollen sensitization, and doctors' diagnosis of hay fever and pollen asthma in German schoolchildren.

BACKGROUND: In order to prevent pollen asthma by immunotherapy it is mandatory to know the best time to initiate it. Children with hay fever complaints are at considerable risk of developing pollen asthma. Population-based data on their natural history is urgently needed. METHODS: A longitudinal cohort study was conducted over four years in six rural towns in Baden-Württemberg, Germany. A questionnaire with questions taken from the International Study of Asthma and Allergies in childhood (ISAAC) was filled in every spring and autumn. Hay fever complaints, asthma defining symptoms and new doctors' diagnosis of hay fever and asthma were recorded. Additionally a skin prick test with pollen allergens was performed every autumn. RESULTS: In 1996, 19.7% of 1101 elementary school children (age: 8.1-9.9 years (5-95%)) were found to be sensitized to pollen and 8.7% had already been diagnosed as having hay fever. In a pooled analysis of 2478 children-summers, children with positive pollen sensitization had a significantly higher risk of developing hay fever symptoms (2.63; 2.17-3.10 odds ratio (OR); 95% confidence interval (CI)) and of being diagnosed as suffering from hay fever (7.88; 4.70-13.20). Furthermore, although their OR for the development of asthma symptoms during the pollen season was 3.88 (2.48-6.07 CI), it was only 0.69 (0.24-2.01 CI) for doctors' diagnosis of pollen asthma. CONCLUSION: Children of elementary school age with pollen sensitization and a history of hay fever are at considerable risk of getting pollen asthma, but they are not quickly diagnosed as such. Specific immunotherapy might be a means of preventing asthma completely in such a situation. Our data helps to estimate the sample size for intervention studies of this kind.

Air Pollutants↗
PubMed2003

Sample Power and ExpDesign: tools for improving design of animal experiments.

Proper experimental design, involving the correct number of animals, should be a basic skill for any scientist working with animals. The authors describe a university-developed and freely available tutorial program and an interactive computer-assisted learning program, both of which guide students through the steps necessary for designing animal experiments and estimating optimal sample sizes.

Analgesics↗
PubMed2004

[Multicenter study on "non-invasive ventilation in patients with severe chronic obstructive pulmonary disease and emphysema(COPD)"].

Non-invasive ventilation is applied with increasing frequency in patients with chronic hypercapnic COPD and insufficiency of the ventilatory pump. In the few existing clinical trials on long-term use of NIV, no significant improvement on survival could be proven, mainly due to methodical reasons. The "National Task Force for Non-invasive ventilation and weaning" plans to study patients with severe COPD and hypercapnic ventilatory pump insufficiency in a prospective, randomised, multicentre clinical trial over one year. In the intervention group, NIV will be applied for at least six hours per day in addition to standard COPD-treatment. The target of mechanical ventilation is a reduction of PCO (2) during spontaneous breathing by at least 20 %, or into the normal range. The main outcome parameter is all-cause mortality, secondary outcome parameters are course of the disease, exercise capacity, quality of life and consumption of medical resources. The sample size is estimated on 300 patients (150 control group, 150 intervention group). The whole study will take approximately three years.

Emphysema↗
PubMed2002

Induced sputum is a reproducible method to assess airway inflammation in asthma.

To evaluate the reproducibility of induced sputum analysis, and to estimate the sample size required to obtained reliable results, sputum was induced by hypertonic saline inhalation in 29 asthmatic subjects on two different days. The whole sample method was used for analysis, and inflammatory cells were counted on cytospin slides. Reproducibility, expressed by intra-class correlation coefficients, was good for macrophages (+0.80), neutrophils (+0.85), and eosinophils (+0.87), but not for lymphocytes (+0.15). Detectable differences were 5.5% for macrophages, 0.6% for lymphocytes, 5.2% for neutrophils, and 3.0% for eosinophils. We conclude that analysis of induced sputum is a reproducible method to study airway inflammation in asthma. Sample sizes greater than ours give little improvement in the detectable difference of eosinophil percentages.

Adolescent↗
PubMed2006

Promoting sexual and reproductive health in early adolescence in South Africa and Tanzania: development of a theory- and evidence-based intervention programme.

AIMS: Action to prevent the spread of HIV among young people in Sub-Saharan Africa is needed urgently. In order to be effective, such action should be theory and evidence based and carefully adapted to local cultures and contexts. The present article describes the organization, theoretical basis, and methodological approach of a project that aims at developing and evaluating school-based interventions targeting adolescents aged 12-14 years. METHODS: Researchers from European and African universities have developed interventions that were conducted in three sites: Cape Town and Polokwane (South Africa) and Dar es Salaam (Tanzania). In each site the interventions were evaluated through large-scale field experiments with intervention schools and delayed intervention schools and with baseline and two follow-up data collections. Minimum sample sizes were estimated for each site based on local data and taking into account that the unit of allocation was schools and not individual students (the design effect). During the formative phase as well as within the field experiments, qualitative studies were also conducted. DISCUSSION: The interventions were developed consistent with the Intervention Mapping approach, and the theoretical framework was based on a modified version of the Theory of Planned Behaviour. The limitations of Western social cognition models were recognized, and the theoretical framework has therefore been expanded in two directions: towards integrating cultural processes and towards taking societal factors and constraints into account. CONCLUSION: The project will throw light on the application of social cognition models as well as the usefulness of the Intervention Mapping approach to intervention development in sub-Saharan Africa.

Adolescent↗