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Results for “Sample size estimation”

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PubMed1988

Unfavourable outcomes of drug therapy--subjective probability versus confidence intervals.

To investigate how individual predictions compare with confidence intervals, we asked 50 medical residents and 28 graduate students with biostatistics training to estimate unfavourable outcomes of drug therapy (therapeutic failures and side-effects) in groups of 10 and 20 patients. The predictions made by physicians and graduate students were similar for both sample sizes and types of outcome. The majority (58%) of estimates were greater than the upper limit of the 95% confidence interval, a bias that may hamper the correct interpretation of therapeutic risks in medical decision-making.

Adult↗
PubMed2002

Assessment of efficient sampling designs for urban stormwater monitoring.

Monitoring programs for urban runoff have not been assessed for effectiveness or efficiency in estimating mass emissions. In order to determine appropriate designs for stormwater, total suspended solids (TSS) and flow information from the Santa Ana River was collected nearly every 15 min for every storm of the 1998 water year. All samples were used to calculate the "true load" and then three within-storm sampling designs (flow-interval, time-interval, and simple random) and five among-storm sampling designs (stratified by size, stratified by season, simple random, simple random of medium and large storms, and the first m storms of the season) were simulated. Using these designs, we evaluated three estimators for storm mass emissions (mean, volume-weighted, and ratio) and three estimators for annual mass emissions (median, ratio, and regular). Designs and estimators were evaluated with respect to accuracy and precision. The optimal strategy was used to determine the appropriate number of storms to sample annually based upon confidence interval width for estimates of annual mass emissions and concentration. The amount of detectable trend in mass emissions and concentration was determined for sample sizes 3 and 7. Single storms were most efficiently characterized (small bias and standard error) by taking 12 samples following a flow-interval schedule and using a volume-weighted estimator of mass emissions. The ratio estimator, when coupled with the simple random sample of medium and large storms within a season, most accurately estimated concentration and mass emissions; and had low bias over all of the designs. Sampling seven storms is the most efficient method for attaining small confidence interval width for annual concentration. Sampling three storms per year allows a 20% trend to be detected in mass emissions or concentration over five years. These results are decreased by 10% by sampling seven storms per year.

Environmental Monitoring↗
PubMed1986

Early invasive carcinoma in colonic polyps. A review of the literature with emphasis on the assessment of the risk of metastasis.

The proper treatment of adenomatous colonic polyps containing small foci of invasive cancer is controversial because the metastatic potential of these lesions is not precisely known. This article critically reviews all known English language studies of this lesion. Before the introduction of colonoscopic polypectomy, the estimated incidence of metastasis from this lesion was 10.4% (based on 12 studies containing 347 polyps), with a confidence interval (95% level) of 7.4 to 14.1. The incidence of metastasis estimated from lesions removed via colonoscopic polypectomy was 10.1% (based on 13 studies containing 188 polyps), with a confidence interval of 5.9 to 14.8. Differences in the definitions of the involved lesions, study designs, and indications for resection cause problems with case selection bias and make comparison of studies difficult. These problems are discussed in detail. Most studies had broad confidence intervals for the estimated incidence of metastasis because of small sample size. The histopathologic criteria, as reflected in the literature, for considering polypectomy alone as adequate treatment for this lesion are summarized and discussed.

Carcinoma↗
PubMed2005

A note on comparing exposure data to a regulatory limit in the presence of unexposed and a limit of detection.

In some occupational health studies, observations occur in both exposed and unexposed individuals. If the levels of all exposed individuals have been detected, a two-part zero-inflated log-normal model is usually recommended, which assumes that the data has a probability mass at zero for unexposed individuals and a continuous response for values greater than zero for exposed individuals. However, many quantitative exposure measurements are subject to left censoring due to values falling below assay detection limits. A zero-inflated log-normal mixture model is suggested in this situation since unexposed zeros are not distinguishable from those exposed with values below detection limits. In the context of this mixture distribution, the information contributed by values falling below a fixed detection limit is used only to estimate the probability of unexposed. We consider sample size and statistical power calculation when comparing the median of exposed measurements to a regulatory limit. We calculate the required sample size for the data presented in a recent paper comparing the benzene TWA exposure data to a regulatory occupational exposure limit. A simulation study is conducted to investigate the performance of the proposed sample size calculation methods.

Algorithms↗
PubMed2004

Immune function and adjustment style: do they predict survival in breast cancer?

The aim of this study was to investigate the role of immune status and psychosocial factors in survival from early breast cancer (N=61). Baseline assessments included lymphocyte number and function, natural killer cell activity (NKA), plasma cortisol and prolactin level. Psychosocial measures included anxiety, depression and mental adjustment to cancer and social support. Length of follow-up was 6.1-7.9 years with 14 (23%) breast cancer deaths. In Cox proportional hazards models adjusting for lymph node status two parameters predicted longer survival, low NKA (HR 29 per LLU, p=0.003) and minimizing the illness adjustment (HR 0.64 per scale point, p=0.012). These data provide little evidence for a psychoneuroimmunological mechanism in the survival from breast cancer. While this study is limited due to small sample size, and therefore the possibility of inflated estimates, longer survival in those minimizing the illness is a finding consistent with recent studies; however, the counter-intuitive finding that high NKA predicts shorter survival may be a marker for current disease or response to treatments.

Adaptation, Psychological↗
PubMed2026

Big data and psychiatry: advances, constraints and future directions.

Early work in psychiatry research, often involving single sites, small samples, and limited variables, has shifted to contemporary research involving multiple sites, large samples, and many variables. Such research raises important questions, including concerns about data quality and methodological rigor, uncertainty about its key lessons, issues regarding clinical relevance, and questions about how to optimize future advances. Here we consider these questions and concerns against the context of big data work on community and register-based surveys, cohort and biobank studies, electronic health records, digital phenotyping, brain imaging, genomics and other -omics, and randomized controlled trials. The development of large datasets allowing well-powered analyses is a major milestone, but sample size alone does not guarantee more precise estimates, and ongoing attention to the quality and rigor of big data collation and analysis is needed. Big data research has fostered trans-disciplinarity and given insights into mechanisms underlying psychiatric disorders, but also emphasizes the intricacy, heterogeneity and variability of such mechanisms, and the importance of triangulating between large-scale and small-scale research. The complexity of psychiatric phenotypes and psychobiological mechanisms contributes to the difficulty in bridging from big data to clinical application; big data research reinforces the importance of holding our diagnoses of psychiatric disorders lightly and providing explanations of these conditions humbly; and future work needs to be more attentive to clinical issues. There is enormous scope for further building databases relevant to psychiatry, but advances in conceptual models and asking the right questions are equally valuable. The full impact of big data, including artificial intelligence analyses, remains to be seen, but overenthusiastic support should be tempered by a better understanding of its strengths and limitations. At its best, such work will contribute in an iterative and integrative way to advancing our knowledge of psychiatric disorders and mental health.

Big data↗
PubMed1996

Statistics for microsatellite variation based on coalescence.

The stepwise mutation model, which was at one time chiefly of interest in studying the evolution of protein charge-states, has recently undergone a resurgence of interest with the new popularity of microsatellites as phylogenetic markers. In this paper we describe a method which makes it possible to transfer many population genetics results from the standard infinite sites model to the stepwise mutation model. We study in detail the properties of pairwise differences in microsatellite repeat number between randomly chosen alleles. We show that the problem of finding the expected squared distance between two individuals and finding the variance of the squared distance can be reduced for a wide range of population models to finding the mean and mean square coalescence times. In many cases the distributions of coalescence times have already been studied for infinite site problems. In this study we show how to calculate these quantities for several population models. We also calculate the variance in mean squared pairwise distance (an estimator of mutation rate x population size) for samples of arbitrary size and show that this variance does not approach zero as the sample size increases. We can also use our method to study alleles at linked microsatellite loci. We suggest a metric which quantifies the level of association between loci-effectively a measure of linkage disequilibrium. It is shown that there can be linkage disequilibrium between partially linked loci at mutation-drift equilibrium.

DNA↗
PubMed1987

A critical reappraisal of cystometry in neurogenic bladder diseases.

Repeated cystometry was performed over an eight hour period in 14 patients with detrusor hyperreflexia. Volumes at first contraction, and at bladder capacity and also bladder compliance showed significant differences within individual variances and an increase in standard deviation in relation to increase in mean value. Amplitude of contractions showed equal variances in all patients. After a logarithmic transformation of the measurements the volume at first bladder contraction showed a significant increase (p less than 0.02) from the first to the second investigation performed an hour later. Determination of sample size in clinical trials using the pooled estimate of the standard deviations is discussed.

Adolescent↗
PubMed1989

The effect of neuroendocrine secretion on brain morphology and EEG sleep in patients with eating disorders.

Neuroendocrine disturbances [low plasma levels of triiodothyronine (T3), high plasma concentrations of cortisol], morphological brain alterations [enlarged external cerebrospinal fluid (CSF) spaces, dilatation of the ventricles] and altered sleep patterns [fragmented sleep continuity, a reduction of slow wave sleep (SWS) or REM sleep] have been described in patients with anorexia nervosa and bulimia nervosa. The present study investigates to what degree these disturbances interact with each other. In ten anorexic and five bulimic patients cranial computed tomography (CT) to estimate the size of the CSF spaces, blood sampling to measure cortisol and T3 plasma concentrations, and all-night polysomnography were performed. In comparison with patients with normal CT scans, the patients displaying enlarged CSF spaces spent more time in SWS, and the duration of REM sleep was reduced. In the whole sample, a negative correlation was found between the amount of REM sleep and cortisol, whereas a positive association was found between the amount of REM sleep and the T3 level. In addition, the degree of brain shrinkage correlated positively with cortisol and negatively with T3. On the basis of these results, it can be assumed that in patients with eating disorders the disease process with its neuroendocrine alterations affects brain morphology as well as EEG sleep.

Brain↗
PubMed1992

Measures of clinical agreement for nominal and categorical data: the kappa coefficient.

The desire to determine the extent inter-rater measurements obtained in a clinical setting are free from measurement error and reflect true scores has spurned a renewed interest in assessment of reliability. The kappa coefficient is considered the statistic of choice to analyze the reliability of nominal and categorical types of data recorded on the same patient by more than one clinician. This paper presents a simple computer program written in PASCAL that can be used in a clinical environment to quickly determine the reliability of nominal or categorical data. This computer program calculates both weighted and non-weighted kappa coefficients with their corresponding standard errors as well as bias-correcting jackknife estimates of kappa for use with small sample sizes.

Data Interpretation, Statistical↗
PubMed1994

The molecular and population genetics of cyclodiene insecticide resistance.

Cyclodiene resistance has accounted for over 60% of reported cases of insecticide resistance. Understanding of this resistance can therefore help us answer questions relating to the mechanism and origin of representative resistance-associated mutations, questions fundamental to the molecular and populations genetics of pesticide resistance. The cyclodiene resistance gene Rdl (resistance to dieldrin) was cloned from a mutant of the model insect Drosophila resistant to cyclodienes and picrotoxinin. Rdl codes for a subunit of a novel class of GABA gated chloride ion channels and resistance is correlated with replacement of the same amino acid residue in a wide range of species from different insect orders. This single amino acid replacement Ala302 > Ser, within the proposed lining of the chloride ion channel, also confers insensitivity to the blocking action of cyclodienes and picrotoxinin on GABA gated chloride ion channels expressed in Xenopus oocytes. The resistance mechanism involves both changes in cyclodiene binding site affinity and also a change in the rate of receptor desensitization which destabilizes the cyclodiene-favored conformation. Documentation of the resistance associated mutation has allowed for the design of a PCR based molecular monitoring technique. This technique gives more accurate estimates of resistance gene frequency from smaller sample sizes and has shown the frequency of resistance in apparently unselected populations of Drosophila to be as high as 1%. We are still uncertain as to why resistance persists in the apparent absence of selection pressure and any severe reduction in the fitness of resistant strains, besides a paralytic phenotype at high temperature, remains undocumented.

Amino Acid Sequence↗
PubMed2006

Audit of preoperative and early complications of laparoscopic lymph node dissection in 1000 gynecologic cancer patients.

OBJECTIVE: Establish the reliability and safety of minimal invasive surgery in gynecologic oncology in a large-scale study. Estimate the complication rate on a large sample size. STUDY DESIGN: From December 1998 to November 2004, 1000 gynecologic cancer patients underwent pelvic and/or aortic lymphadenectomies by laparoscopy. A total of 1192 pelvic and aortic lymphadenectomies have been performed: 777 pelvic (757 transperitoneal, 20 extraperitoneal) and 415 aortic lymphadenectomies (155 transperitoneal, 260 extraperitoneal). Main indications for laparoscopic lymph node dissection were: early cervical carcinoma (n = 456), advanced cervical carcinoma (n = 219), vaginal carcinoma (n = 4), endometrial carcinoma (n = 182), and ovarian carcinoma (n = 139). Surgical laparoscopic management via laparoscopy was achieved during the same operative session in 372 patients. RESULTS: No lethality occurred. Thirteen open surgeries (1.3%) were required as a result of failure to complete a satisfactory laparoscopic procedure. Intraoperative, early postoperative complication rate, and lymphocyst formation rate were 2.0%, 2.9%, and 7.1%, respectively. A laparotomy was required for complication in seven patients (7 per 1000), including five returns to operating room. Eleven significant intraoperative vascular injuries occurred, but none required a laparotomy. The most frequently encountered visceral complications were bowel complications (n = 7), urinary tract complications (n = 5), and nerve injuries (n = 5). CONCLUSION: Evidence is given on a large series that laparoscopic lymph node dissection is safe. Laparoscopic surgery may be considered as the gold standard of assessment of the status of regional lymph nodes in gynecologic malignancies.

Adolescent↗
PubMed2004

Comparison of rapidity of coronary recanalization in men with tenecteplase versus alteplase in acute myocardial infarction.

To determine whether tenecteplase (TNK-t-PA), a bioengineered variant of tissue-type plasminogen activator (t-PA) designed to accelerate thrombolysis, exhibits favorable properties compared with those of alteplase, 266 men were studied </=6 hours after the onset of symptoms and signs of acute myocardial infarction. The primary end point was the rapidity of recanalization as judged from analysis of serial changes in the concentrations in blood of isoforms of creatine kinase-MM in serially obtained blood samples. Additional end points included enzymatically estimated infarct size and mortality. Patients were treated quite promptly after the onset of symptoms. The interval from the onset of chest pain to recanalization seen with TNK-t-PA was 208 +/- 10 (SE) minutes compared with 237 +/- 9 minutes seen with alteplase (p = 0.04). Thirty-day mortality was low with the use of the 2 agents (2%). TNK-t-PA appears to induce recanalization more rapidly than alteplase, and thrombolysis initiated early after the onset of symptoms is associated with remarkably low mortality.

Adult↗
PubMed2004

Influence of smoking on incidence and prevalence of peripheral arterial disease.

OBJECTIVE: Many studies have been published regarding the influence of smoking on the incidence and prevalence of peripheral arterial disease (PAD). A systematic review was performed to establish the magnitude of the effect of smoking on the development of PAD, and a possible dose-response relationship. METHODS: English-language articles were reviewed by 2 observers using a standardized form, and were summarized in tabular form. Data were extracted by 2 independent observers. Where possible, outcome data, expressed in terms of prevalence or incidence, were recalculated as odds ratio or relative risk, with never-smokers as the reference group, or if this was not available the nonsmoker group. Most studies did not provide primary data. Therefore the weighted means were reported as a summary estimate, provided that a funnel plot between sample size and observed effect size made publication bias unlikely. RESULTS: Sixteen articles describing 17 studies were included in the analysis. Four of the studies were prospective, and 13 were cross-sectional. The prevalence of symptomatic PAD was increased 2.3-fold in current smokers. Even in former smokers the prevalence was substantially increased by a factor of 2.6. A clear dose-response relationship, with a strong increase in risk for PAD in heavy smokers was observed. In countries where approximately 30% of the population are smokers, 50% of PAD can be attributed to smoking. CONCLUSIONS: Smoking is a potent risk factor for symptomatic PAD, with an important and consistent dose-response relationship. With the persistence of high risk for PAD in former smokers, tobacco control programs should continue to advocate smoking cessation, but focus even more on preventing future generations from ever starting to smoke.

Adult↗
PubMed1998

Sensitivity, specificity, and vaccine efficacy.

We study the effects of imperfect sensitivity and specificity on estimation of vaccine efficacy (VE). We show that a specificity of <1.0 (i.e., some noncases are classified as cases) can reduce the value of the estimate of VE. One may attempt to adjust the estimate by accounting for the values of sensitivity and specificity. This increases the variance of the estimate of VE and leads to larger sample size requirements. Alternatively, one may adopt the diagnosis method as the disease definition.

Analysis of Variance↗
PubMed2006

[Birthweight curves: a review of the literature].

There are many birthweight reference curves in the literature. This study reviews birthweight curves that are commonly used in France as well as references that provide birthweight by sex. The 19 curves selected for review were published between 1971 and 2001 using samples of between 300 to 3 million newborns in Europe, Australia and North America. Our objective was to summarize their main characteristics and to provide guidelines for analysis by explaining which factors are responsible for differences between curves, and discussing the methods used to construct them. The characteristics of the population must be taken into account and study samples must be recent and representative. The sample size must be sufficient to ensure stable estimates for premature infants. It is preferable to use different curves for boys and girls because sex is a key determinant of birth weight. The choice of appropriate birth weight reference remains difficult in some countries, in France particularly, and the use of individual customised birth weight curves provides an interesting alternative.

Birth Weight↗
PubMed2000

Relationships of sweet, bitter, and roasted peanut sensory attributes with carbohydrate components in peanuts.

Certain roasted peanut quality sensory attributes have been shown to be heritable. Currently the only means of measuring these traits is the use of a trained sensory panel. This is a costly and time-consuming process. It is desirable, from a cost, time, and sample size perspective, to find other methodologies for estimating these traits. Because sweetness is the most heritable trait and it has a significant positive relationship to the roasted peanut trait, the possible relationships between heritable sensory traits and 18 carbohydrate components (inositol, glucose, fructose, sucrose, raffinose, stachyose, and 12 unknown peaks) in raw peanuts from 52 genotypes have been investigated. Previously reported correlations among sweet, bitter, and roasted peanut attributes were evident in this study as well. Where there was positive correlation of total sugars with sweetness, there also was positive correlation of total sugars with roasted peanut attribute and negative correlation of total sugars with bitterness and astringency. The expected generalized relationship of total sugars or sucrose to sweetness could not be established because the relationship was not the same across all market-types. Further work is needed to determine the nature of the chemical components related to the bitter principle, which appear to modify the sweet response and interfere with the sensory perception of sweetness, particularly in the Virginia market-type. Also, certain carbohydrate components showed significant relationships with sensory attributes in one market-type and not another. These differential associations demonstrate the complexity of the interrelationships among sweet, bitter, and roasted peanut sensory attributes. Within two market-types it is possible to improve the efficiency of selection for sweetness and roasted peanut quality by assaying for total carbohydrates. On the basis of the regression values the greatest efficiency would occur in the fastigiate market-type and then the runner.

Arachis↗
PubMed2005

Cost/variance optimization for human exposure assessment studies.

The National Human Exposure Assessment Survey (NHEXAS) field study in EPA Region V (one of three NHEXAS field studies) provides extensive exposure data on a representative sample of 249 residents of the Great Lakes states. Concentration data were obtained for both metals and volatile organic compounds (VOCs) from multiple environmental media and from human biomarkers. A variance model for the logarithms of concentration measurements is used to define intraclass correlations between observations within primary sampling units (PSUs) (nominally counties) and within secondary sampling units (SSUs) (nominally Census blocks). A model for the total cost of the study is developed in terms of fixed costs and variable costs per PSU, SSU, and participant. Intraclass correlations are estimated for media and analytes with sufficient sample sizes. We demonstrate how the intraclass correlations and variable cost components can be used to determine the sample allocation that minimizes cost while achieving pre-specified precision constraints for future studies that monitor environmental concentrations and human exposures for metals and VOCs.

Biomarkers↗