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At least 217 records · Page 12Linked to original sources
PubMed2005

Continuous toxicity monitoring in phase II trials in oncology.

The goal of a phase II trial in oncology is to evaluate the efficacy of a new therapy. The dose investigated in a phase II trial is usually an estimate of a maximum-tolerated dose obtained in a preceding phase I trial. Because this estimate is imprecise, stopping rules for toxicity are used in many phase II trials. We give recommendations on how to construct stopping rules to monitor toxicity continuously. A table is provided from which Pocock stopping boundaries can be easily obtained for a range of toxicity rates and sample sizes. Estimation of the probability of toxicity and response is also discussed.

Bayes Theorem↗
PubMed2001

Photographic measures of cytomegalovirus retinitis as surrogates for visual outcomes in treated patients.

OBJECTIVE: To evaluate photographic measures of cytomegalovirus (CMV) retinitis as surrogate outcomes for changes in vision in patients with CMV retinitis related to the acquired immunodeficiency syndrome. METHODS: Data from 3 clinical trials of CMV retinitis treatments were analyzed. Two photographic assessments of retinitis in eyes involved at baseline were evaluated: progression (lesion border movement > or = 750 microm or occurrence of a new lesion) and change in area of retina involved with retinitis. Vision measures were decline in best-corrected visual acuity and change in visual field. Photographic measures were evaluated as surrogate outcomes based on 4 criteria: (1) association with vision measure; (2) ability to account for treatment-related differences in vision measure; (3) data completeness; and (4) sample size requirements. RESULTS: Data from 1001 involved eyes (666 patients) were analyzed. Progression and change in area involved were predictive of declines in vision measures, accounted for 50% and 66% of the treatment effect on visual field, and were available from 93% and 64% of involved eyes, respectively. Sample size estimates for a clinical trial were smallest with progression as the design outcome. CONCLUSION: Progression and change in area involved met the first and second criteria for surrogate outcomes for visual field loss; a complete evaluation for visual acuity decline was not possible because treatment-related differences were not observed. Progression met the logistical and sample size criteria better than change in area of retina involved with retinitis.

AIDS-Related Opportunistic Infections↗
PubMed1987

Sample size in the planning and interpretation of clinical trials.

An understanding of sample size determination is important in both planning and interpreting the results of clinical trials. A Type II error occurs when it is concluded that there is no difference between treatment groups, when in truth there is a difference. Such a false negative conclusion results from too few patients in a trial. In this review the principles of estimating sample size before a trial is commenced and evaluating the results of a negative completed trial are reviewed. Clinically relevant examples are used to illustrate these concepts.

Biometry↗
PubMed1996

Mutational spectra in transgenic animal research: data analysis and study design based upon the mutant or mutation frequency.

Understanding chemically induced changes in mutational spectra can aid in deciphering mechanisms of mutagenesis. In this paper, we propose the use of statistical methods that are based upon the mutation frequency, rather than simple mutant counts which have no relationship to the mutation frequency. These methods have a number of advantages over the current standard analysis: an improved means of identifying those classes/sites of mutation which have treatment-related induction, greater sensitivity to localized differences in spectra (e.g., limited to a single base pair), one-sided tests for induction of mutations, tests of dose-response, and a framework for sample-size estimation in terms of the number of mutants to sequence. As examples, the methods are applied to data from transgenic mutation assays.

Animals↗
PubMed2005

Bilateral symmetry of the human metacarpal: implications for sample size calculations.

OBJECTIVE: The aim of this study was to assess the three-dimensional mechanical symmetry of the human second metacarpal and provide sample size estimates for future mechanical intervention studies of the metacarpal. DESIGN: Bone densitometry and digital image analysis were used to assess the morphometric, geometric and densitometric symmetry of the second human metacarpal. BACKGROUND: An assessment of the left-right mechanical symmetry of the human metacarpal is important in considering the suitability of using the contralateral metacarpal as a control and in providing sample size calculations for future studies involving a mechanical intervention to the metacarpal such as implantation of a metacarpophalangeal prosthesis. METHODS: Metaphyseal sectional areas, diaphyseal cortical sectional areas, second moments of area, average periosteal and medullary radii and bone densities were measured at nine transverse levels for each of seven pairs of index metacarpals using computed tomography and bone densitometry. Polar Fourier regression was used to assess the morphometry of sectional periosteal and endosteal boundaries. Differences between clinically important left-right parameters were assessed. RESULTS: Mean differences between clinically important left-right parameters were small (<3%) and similar to the degree of experimental precision. There were strong significant left-right correlations for the morphometric, geometric and densitometric parameters considered, indicating a high degree of bilateral mechanical symmetry. CONCLUSIONS: The contralateral bone is a suitable control for mechanical intervention studies of the human metacarpal, and the use of bilateral pairing results in an important reduction in sample size. RELEVANCE: Responses to mechanical interventions on the human metacarpal, such as implantation of a metacarpophalangeal prosthesis, are generally unknown. The degree of left-right mechanical symmetry in the human metacarpal provides a measure of the advantage of using paired design studies to address these questions.

Anatomy, Cross-Sectional↗
PubMed2002

FIM after hip fracture: is telephone administration valid and sensitive to change?

OBJECTIVES: It has been reported recently that follow-up FIM trade mark scores have been obtained from stroke patients via telephone interviews with either the former patient or proxy caregivers. We studied the validity and sensitivity of change of a "phone FIM" score in a sample of hip fracture patients after rehabilitation. DESIGN: We compared FIM scores among hip fracture patients in a specialized musculoskeletal rehabilitation program. Sample size estimate of 27 was determined before the study. Patients included those with hip fracture returning to independent living in their own home. RESULTS: Twenty-nine patients were identified as a convenience sample of admitted patients. The phone FIM score at 8 wk was a valid predictor of the discharge FIM score and the observed FIM and phone FIM scores at 8 wk were similar. The sensitivity to change over 8 wk was similar between observed and phone FIM scores compared with the discharge FIM score. CONCLUSIONS: The phone FIM instrument presents a useful clinical instrument to monitor patient functional status in the community, showing excellent psychometric properties. Ease of use and low cost should encourage greater use in clinical management of these patients.

Activities of Daily Living↗
PubMed2004

Incidence of severe Plasmodium falciparum malaria as a primary endpoint for vaccine efficacy trials in Bandiagara, Mali.

Potential endpoints for blood stage malaria vaccine efficacy trials include uncomplicated malaria disease, which is hard to differentiate from other febrile illnesses, and mortality, which requires prohibitively large sample sizes. Strictly defined severe malaria predicts malaria-associated mortality where case fatality rates are known. To assess the suitability of severe malaria as a trial endpoint, we conducted a census in 1999 and measured the incidence of severe malaria from 1999 to 2001 in Bandiagara, Mali. The annual incidence of severe malaria in children <6 years of age was 2.3% (n = 2,284) yielding an estimated sample size of 4,580 for a vaccine trial designed to detect 50% efficacy with 80% power at P = 0.05 with 5% loss to follow-up. A trial using severe malaria as an endpoint in this setting would thus require expanding the study population or the length of the trial. This approach may be useful in assessing the suitability of potential sites for malaria vaccine trials.

Child↗
PubMed2004

Sampling strategies for prospective studies of menstrual function.

Little information is available about optimal sampling strategies for prospective studies of menstrual function. Sample size and study duration for menstrual studies have often been driven as much by feasibility and cost as by statistical principles, with follow-up lasting 6 months to 2 years and sample size ranging from 100 to 500 women. Whether these studies are sufficiently powered to address common study objectives has not been adequately evaluated, and sample size estimates rarely account for the repeated nature of menstrual cycle data. Using data from the Tremin Trust (a study of menstrual function across the reproductive life span initiated in Minneapolis, Minnesota, in 1935 with data collected through 1977), the authors determined sampling strategies for assessing differences in mean cycle length between two exposure groups and for assessing change in mean cycle length across the reproductive life span. Following a larger number of women for 1-2 years is optimal for studies of host and environmental exposures that alter menstrual function. In contrast, following fewer women for an extended period of time, for example, 4-5 years, is optimal when studying how menstrual patterns vary across the reproductive life span in different populations.

Adolescent↗
PubMed2005

The quality of randomized controlled trials in major anesthesiology journals.

Increased attention has been directed at the quality of randomized controlled trials (RCTs) and how they are being reported. We examined leading anesthesiology journals to identify if there were specific areas for improvement in the design and analysis of published clinical studies. All RCTs that appeared between January 2000 and December 2000 in leading anesthesiology journals (Anesthesiology,Anesthesia & Analgesia,Anaesthesia, and Canadian Journal of Anaesthesia) were retrieved by a MEDLINE search. We used a previously validated assessment tool, including 14 items associated with study quality, to determine a quality score for each article. The overall mean weighted quality score was 44% +/- 16%. Overall average scores were relatively high for appropriate controls (77% +/- 7%) and discussions of side effects (67% +/- 6%). Scores were very low for randomization blinding (5% +/- 2%), blinding observers to results (1% +/- 1%), and post-beta estimates (16% +/- 13%). Important pretreatment clinical predictors were absent in 32% of all studies. Significant improvement in the reporting and conduct of RCTs is required and should focus on randomization methodology, the blinding of investigators, and sample size estimates. Repeat assessments of the literature may improve the adoption of guidelines for the improvement of the quality of randomized controlled trials.

Anesthesiology↗
PubMed2007

Accounting for expected attrition in the planning of community intervention trials.

Trials in which intact communities are the units of randomization are increasingly being used to evaluate interventions which are more naturally administered at the community level, or when there is a substantial risk of treatment contamination. In this article we focus on the planning of community intervention trials in which k communities (for example, medical practices, worksites, or villages) are to be randomly allocated to each of an intervention and a control group, and fixed cohorts of m individuals enrolled in each community prior to randomization. Formulas to determine k or m may be obtained by adjusting standard sample size formulas to account for the intracluster correlation coefficient rho. In the presence of individual-level attrition however, observed cohort sizes are likely to vary. We show that conventional approaches of accounting for potential attrition, such as dividing standard sample size formulas by the anticipated follow-up rate pi or using the average anticipated cohort size m pi, may, respectively, overestimate or underestimate the required sample size when cluster follow-up rates are highly variable, and m or rho are large. We present new sample size estimation formulas for the comparison of two means or two proportions, which appropriately account for variation among cluster follow-up rates. These formulas are derived by specifying a model for the binary missingness indicators under the population-averaged approach, assuming an exchangeable intracluster correlation coefficient, denoted by tau. To aid in the planning of future trials, we recommend that estimates for tau be reported in published community intervention trials.

Canada↗
PubMed1998

Determination of sample sizes for the estimation of Onchocerca volvulus (Filarioidea: Onchocercidae) infection rates in biting populations of Simulium ochraceum s.l. (Diptera: Simuliidae) and its application to ivermectin control programs.

Monthly samples of biting Simulium ochraceum s.l. Walker were collected before and after ivermectin treatment in southern Mexico and analyzed for Onchocerca volvulus Leuckart infection rates, infection intensity, and the characteristics of larval distribution among parous flies. The variance over mean ratio (VMR) indicated that in all cases this distribution departed from Poisson and was strongly aggregated (VMR > 1). The negative binomial was found to be an adequate model with a small value of the aggregation parameter k, but the degree of larval overdispersion increased as the mean larval load decreased, invalidating the use of a common kc value. A linear relationship between k and the mean (mu) was established, k(mu) = k1 mu, which permitted exploration of the relationship between the observed proportion of infected flies, p, and the estimated mean larval burden per fly, m (all larval stages in parous flies). This would allow mean numbers of larvae per parous fly to be predicted from presence-absence data (e.g., from infection rates provided by polymerase chain reaction methods applied to pools of flies), assuming that k1 is a known parameter. Given that both p and m are naturally low in S. ochraceum, their relationship was practically linear within the range of observed values. Predictions were tested with the Mexican data from which the clumping parameter was estimated as well as for Guatemalan data for which this information was not available. Results showed a highly satisfactory degree of agreement between predictions and observations. The sample sizes required to estimate mean larval loads from prevalence data for fixed levels of precision (defined as the ratio between SE[m] and m) were calculated for realistic S. ochraceum infection rates (those found in published pre- and postcontrol field surveys as well as in this work). For the special case in which the relationship between k and the mean is linear and goes through the origin, k(mu) = k1 mu, the number of flies to be examined for O. volvulus infections does not explicitly depend on the aggregation parameter, but rather on the unknown proportion of infected flies. Practical recommendations for the calculation of sample sizes are discussed. For infection levels < 0.2%, a minimum number between 6,000 and 13,000 parous flies would have to be examined to estimate the mean larval load with a precision between 0.20 and 0.30. The linearity between onchocercal infection rate and infection intensity in the fly population indicates that relationships between the former and onchocerciasis patterns in the human population should be further explored for the purposes of monitoring the impact of ivermectin control programs through entomological evaluations.

Animals↗
PubMed2005

A randomized controlled trial of beta-blockers versus endoscopic band ligation for primary prophylaxis: a large sample size is required to show a difference in bleeding rates.

Primary prophylaxis with nonselective beta-blockers in high-risk subjects has been shown to be effective in reducing both esophageal variceal bleeding and mortality. Recently it has been suggested that band ligation may be a better option for primary prophylaxis. We compared nonselective beta-blockers with band ligation in patients with large varices (F2, F3) and elevated hepatic venous wedge pressure gradient (HVWPG, > or = 12 mm Hg). All patients were prospectively followed for variceal bleeding, mortality, and treatment-related complications. Based on previous published studies, we estimated that 90 patients in each arm would be required to show a difference in bleeding rate. The study was prematurely terminated when we realized that our estimated sample size was inadequate to show a difference based on the observed bleeding rate. At the time of termination, 31 patients (Child A, 11; B, 14; C, 6), with a mean HVWPG of 19 +/- 9.1 mm Hg, were randomized to either band ligation (group A; n = 16) or beta-blockers (group B; n = 15). Baseline demographics of both groups were similar and the mean follow-up period was 27.4 +/- 12.9 months. During the follow-up, two patients in group A and one patient in group B had bleeding. Nine patients (29%; group A, six; group B, three; P = ns) died due to non-bleeding-related causes and five (16%) patients (group A, three; group B, two) underwent liver transplantation. Treatment-related complication were minimal in both groups. Despite the selection of high-risk patients, the observed bleeding rate was much lower than anticipated. Based on our observed bleeding rates, 424 patients would be required in each arm to show a difference between band ligation and beta-blocker therapy.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Monitoring nekton as a bioindicator in shallow estuarine habitats.

Long-term monitoring of estuarine nekton has many practical and ecological benefits but efforts are hampered by a lack of standardized sampling procedures. This study provides a rationale for monitoring nekton in shallow (< 1 m), temperate, estuarine habitats and addresses some important issues that arise when developing monitoring protocols. Sampling in seagrass and salt marsh habitats is emphasized due to the susceptibility of each habitat to anthropogenic stress and to the abundant and rich nekton assemblages that each habitat supports. Extensive sampling with quantitative enclosure traps that estimate nekton density is suggested. These gears have a high capture efficiency in most habitats and are small enough (e.g., 1 m2) to permit sampling in specific microhabitats. Other aspects of nekton monitoring are discussed, including spatial and temporal sampling considerations, station selection, sample size estimation, and data collection and analysis. Developing and initiating long-term nekton monitoring programs will help evaluate natural and human-induced changes in estuarine nekton over time and advance our understanding of the interactions between nekton and the dynamic estuarine environment.

Animals↗
PubMed1993

Recruitment and screening experience for a clinical trial involving tear concentrations of a new drug.

The process of recruitment and screening of volunteers for clinical research studies has not been thoroughly evaluated in the ophthalmic literature. The data for the current report were derived from a double-masked randomized clinical trial designed to evaluate and compare the effective tear level concentrations of three topical ophthalmic medications. Subjects were recruited from the general population and were healthy volunteers on no medications. Tear volume was measured by the Schirmer test with anesthesia; acceptable results were in the range of 10-25 mm/5 min. Study enrollment was limited to 32 subjects per week, with a total sample size goal of 320. The study population, 18-45 years of age, consisted primarily of white male college students. Nine hundred fifty-seven volunteers were recruited. Of the 498 of these subjects that reported for screening (52%), 459 (48%) were actually screened, and 320 (33%) were enrolled. The overall prevalence of an abnormal Schirmer test (< 10 or > 25 mm/5 min in either eye) in the screened population was 22%. The frequency of decreased tear production (13%) was slightly greater than that of increased tear production (9%). An abnormal Schirmer test was the primary reason for ineligibility. The completion rate for those enrolled was 96%. This type of information is valuable when designing a clinical trial, especially with regard to budgetary, time table, and sample size estimations.

Adolescent↗
PubMed1999

Clinical trials design: structure modifying agents for osteoarthritis. Future guidelines: areas for development.

Clinical trials guidelines should offer evidence-based recommendations, and, where evidence is lacking or absent, should reflect the considered opinion of experts in the field. Recent OsteoArthritis Research Society International (OARSI) guidelines encompass these principles and are the result of a Task Force Workshop involving representatives from academia, regulatory authorities and industry. Areas for continued development for trials of Structure Modifying Osteoarthritis Drugs (STMOAD) include patient selection, study duration, sample size estimation, outcome assessment, imaging, response definition and pharmoeconomics. As developments occur in these and related areas, guideline documents will require revision to reflect this evolution. Notwithstanding these issues, there is opportunity to identify STMOAD class agents using current methodologies.

Clinical Trials as Topic↗
PubMed2006

WHO systematic review of prevalence of chronic pelvic pain: a neglected reproductive health morbidity.

BACKGROUND: Health care planning for chronic pelvic pain (CPP), an important cause of morbidity amongst women is hampered due to lack of clear collated summaries of its basic epidemiological data. We systematically reviewed worldwide literature on the prevalence of different types of CPP to assess the geographical distribution of data, and to explore sources of variation in its estimates. METHODS: We identified data available from Medline (1966 to 2004), Embase (1980 to 2004), PsycINFO (1887 to 2003), LILACS (1982 to 2004), Science Citation index, CINAHL (January 1980 to 2004) and hand searching of reference lists. Two reviewers extracted data independently, using a piloted form, on participants' characteristics, study quality and rates of CPP. We considered a study to be of high quality (valid) if had at least three of the following features: prospective design, validated measurement tool, adequate sampling method, sample size estimation and response rate >80%. We performed both univariate and multivariate meta-regression analysis to explore heterogeneity of results across studies. RESULTS: There were 178 studies (459975 participants) in 148 articles. Of these, 106 studies were (124259 participants) on dysmenorrhoea, 54 (35973 participants) on dyspareunia and 18 (301756 participants) on noncyclical pain. There were only 19/95 (20%) less developed and 1/45 (2.2%) least developed countries with relevant data in contrast to 22/43 (51.2%) developed countries. Meta-regression analysis showed that rates of pain varied according to study quality features. There were 40 (22.5%) high quality studies with representative samples. Amongst them, the rate of dysmenorrhoea was 16.8 to 81%, that of dyspareunia was 8 to 21.8%, and that for noncyclical pain was 2.1 to 24%. CONCLUSION: There were few valid population based estimates of disease burden due to CPP from less developed countries. The variation in rates of CPP worldwide was due to variable study quality. Where valid data were available, a high disease burden of all types of pelvic pain was found.

Chronic Disease↗
PubMedDate not supplied

Practical issues in survey sampling.

This discussion reviews the principles of survey sampling and applies these principles in a study examining nurses' skills (N = 15,540). Three major facets of sampling are outlined-the sample frame, the sample size and the specific design of the selection procedures. The characteristics of a sample frame, precision in sample size estimation, and rules to be used in the selection procedures, are outlined. In addition, the authors recommend how to obtain assistance with these complex procedures and some steps in problem-solving. This paper provides guidance that will enable nurse researchers, using survey methods, to obtain sample estimates that closely resemble the population.

Clinical Nursing Research↗
PubMed2005

[Prevalence of overactive bladder in Spain: a population-based study].

OBJECTIVES: The aim of this study was to assess the prevalence of the urinary symptoms suggestive of overactive bladder (OAB) in Spain based on the International Continence Society (ICS) 2002 consensus criteria as urinary urgency, with or without urge incontinence, usually with frequency and nocturia. METHODS: 1,669 real telephone interviews were conducted to adults aged > or = 40 years. The sample size estimation was made according to the prevalence for OAB described in the Milsom paper stratified by age and gender due to the high variability observed between ranges. Appearance and prevalence of main OAB symptoms, medical diagnostic and therapy due to these symptoms data were collected. RESULTS: the sample population was 1669 aged > or = 40 years, 50.6% women and 49.4% men. The overall prevalence of symptoms suggestive of OAB according to the OAB definition from ICS report 2002 was 21.5%, significantly higher in women (25.6%) than men (17.4%)(p<0.05). Adjusting these data to Spanish National Census of year 2000, the prevalence was 19.9%, being higher as well in women (23.6%) than men (115.4%). Urge urinary incontinence and stress urinary incontinence were superior in women (16.7% vs 10.4% and 33.1% vs 7.9% respectively)(p<0.01). Urinary frequency > 8 voids/day was referred by 9.8% of women and 7.9% of men interviewed. 62% of men and 52.4% of women reported they get up at night to void. A total of 52.1% of patients with urinary symptoms suggestive of overactive bladder reported they had consulted a doctor anytime before the interview due to urinary disorders and 16.7% was currently receiving treatment for some of these symptoms. CONCLUSIONS: Prevalence of urinary symptoms suggestive of Overactive Bladder is high in this study, in accordance with data from international studies. Urinary urgency, symptom which defines the pathology, is more prevalent in Spanish women than men. Further studies are needed to better assess OAB impact in the Spanish general population.

Adult↗