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PubMed1980

Statistical methods for measuring and comparing treatment efficacies: applications to nude mice experimentation.

A method is proposed for measuring and comparing the growth over time of a sample of tumors subjected to a number of different therapies. The procedure, which is illustrated by means of an example, does not require explicit parametric modelling of the growth curve itself and is particularly useful when the comparison of treatment efficacies is of chief interest. In addition, an ad hoc approach to the estimation of required sample sizes is delineated.

Animals↗

PubMedDate not supplied

Whole blood impedance platelet aggregometry and ischemic heart disease. The Caerphilly Collaborative Heart Disease Study.

The Caerphilly Collaborative Heart Disease Study is based on a large cohort of men who were ages 49 to 64 years at the time of the study. We report the results for platelet aggregation measured in whole blood from a subsample of 308 men. The index of sensitivity used was the minimum concentration of adenosine diphosphate that produced a defined degree of impedance change in the Chronolog 560 aggregometer. There was a marked association between aggregation and prevalent ischemic heart disease (IHD). The odds ratios and 95% confidence intervals (CI) for prevalent IHD in men with the most sensitive platelets compared with those with the least sensitive platelets were 3.6 (95% Cl: 1.1 to 12.2) for angina; 7.3 (95% Cl: 2.0 to 24.3) for previous myocardial infarction (MI); and 2.7 (95% Cl: 1.0 to 7.6) for electrocardiogram evidence of ischemia. The confidence limits for these odds ratios are large because of the small sample size, but the estimates of odds ratio are relatively large compared to similar relationships between the traditional risk factors of serum cholesterol, blood pressure, smoking, and prevalent IHD (1.5 to 2.5). A number of factors that might confound the relationships between platelets and IHD were examined, but the associations remained statistically significant when these were taken into account.

Adenosine Diphosphate↗

PubMed1980

Within-subject variability and per cent change for significance of spirometry in normal subjects and in patients with cystic fibrosis.

We studied 15 normal subjects and 15 patients with cystic fibrosis (CF), to determine the within-subject variability of spirometry, moment analysis, and slope ratios, and to calculate the per cent change for significance. Common sources of variability, such as patient and technician training, equipment errors, lung volume history, posture, and circadian variation, were controlled. Flow-time curves were analyzed with a digital computer. The coefficient of variations of spirometry were smallest for forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak flow (PF), and were largest for root moments (M) and slope ratios (SR) in both normal subjects and patients with CF. The coefficient of variations of all tests, except PF, were larger in patients with CF than in normal subjects. Significant change was calculated from the sample variance, mean, and the number of trials using a modified equation for sample size. This calculation estimated the degree of change for significance for each participant that was required in subsequent testing.

Adolescent↗

PubMed1998

The adequacy of reporting randomized, controlled trials in the evaluation of antidepressants.

OBJECTIVE: To evaluate the adequacy of the reports of methodological and statistical aspects of randomized, controlled trials that evaluate antidepressant medications and the degree to which their results can be used in subsequent metaanalyses. DATA SOURCES: Randomized, controlled trials published in English that compared 2 antidepressant drugs with a placebo were reviewed. Papers were located using Medline and reference lists. DATA EXTRACTION: Each paper was evaluated using a checklist, and 3 summary criteria scores were derived: minimal, ideal, and overall. RESULTS: Only 9 of the 69 papers met the minimal criteria to be included in a metaanalysis (which would report the final sample size and an estimate of the mean and of the standard deviation); and 0 met all of the ideal criteria for reporting clinical trials. Out of a possible 100 points, the mean score for the articles was 51, and the highest score was 80. Scores were not related to the citation impact factor of the journal in which they appeared. CONCLUSIONS: Researchers must become more aware of the criteria for reporting clinical trials, and editors must insist more strenuously that these criteria be satisfied.

Antidepressive Agents↗

PubMed2001

Intraclass correlation for measures from a middle school nutrition intervention study: estimates, correlates, and applications.

This article presents the first estimates of school-level intraclass correlation for dietary measures based on data from the Teens Eating for Energy and Nutrition at School study. This study involves 3,878 seventh graders from 16 middle schools from Minneapolis-St. Paul, Minnesota. The sample was 66.8% White, 11.2% Black, and 7.0% Asian; 48.8% of the sample was female. Typical fruit and vegetable intake was assessed with a modified version of the Behavior Risk Factor Surveillance System questionnaire. Twenty-four-hour dietary recalls were conducted by nutritionists using the Minnesota Nutrition Data System. Mixed-model regression methods were used to estimate variance components for school and residual error, both before and after adjustment for demographic factors. School-level intraclass correlations were large enough, if ignored, to substantially inflate the Type I error rate in an analysis of treatment effects. The authors show how to use the estimates to determine sample size requirements for future studies.

Adolescent↗

PubMed2003

A framework for power analysis using a structural equation modelling procedure.

BACKGROUND: This paper demonstrates how structural equation modelling (SEM) can be used as a tool to aid in carrying out power analyses. For many complex multivariate designs that are increasingly being employed, power analyses can be difficult to carry out, because the software available lacks sufficient flexibility. Satorra and Saris developed a method for estimating the power of the likelihood ratio test for structural equation models. Whilst the Satorra and Saris approach is familiar to researchers who use the structural equation modelling approach, it is less well known amongst other researchers. The SEM approach can be equivalent to other multivariate statistical tests, and therefore the Satorra and Saris approach to power analysis can be used. METHODS: The covariance matrix, along with a vector of means, relating to the alternative hypothesis is generated. This represents the hypothesised population effects. A model (representing the null hypothesis) is then tested in a structural equation model, using the population parameters as input. An analysis based on the chi-square of this model can provide estimates of the sample size required for different levels of power to reject the null hypothesis. CONCLUSIONS: The SEM based power analysis approach may prove useful for researchers designing research in the health and medical spheres.

Analysis of Variance↗

PubMed2005

Efficacy of the epidural blood patch for the treatment of post lumbar puncture headache BLOPP: a randomised, observer-blind, controlled clinical trial [ISRCTN 71598245].

BACKGROUND: Post dural punction headache (PDPH) occurs in 10% to 40% of the patients who had a lumbar puncture. Its symptoms can be severe and incapacitating. The epidural blood patch is widely accepted as the treatment of choice for postdural puncture headache. Uncontrolled studies report rapid recovery after patching in 90% to 100% of treated patients. However, sufficient evidence from randomised, controlled clinical trials is lacking. METHODS: BLOPP (blood patch for post dural puncture headache) is a randomised, single centre, observer-blind clinical trial. Patients with PDPH for at least 24 hours and at most 7 days after lumbar puncture will be randomised to treatment with an epidural blood patch (EDBP) or to conventional treatment, i.e. 24 hours bed rest and ample fluid intake. PDPH 24 hours after treatment, classified on a 4-point scale (no, mild, moderate, severe) is the primary outcome. The secondary outcome is the presence of PDPH 7 days after treatment. We estimated that a sample size of 2 x 20 patients would provide us with a power of 80% to detect a relative reduction in number of patients with persisting PDPH after 24 hours of 50% at the usual significance level alpha = 5%, taking into account that in approximately 10% of the patients the PDPH will have resolved spontaneously after one day. DISCUSSION: The EDBP is accepted as the treatment of choice for PDPH although randomised, controlled data is scarce. Our randomised, observer-blind clinical trial enables us to compare the efficacy of two clinically practiced methods of PDPH treatment; EDBP versus conventional treatment, as they are applied in clinical practise.

Adolescent↗

PubMed2002

Analysis of variance frameworks in clinical child and adolescent psychology: advanced issues and recommendations.

Explores more advanced issues that researchers need to consider when using analysis of variance frameworks, building on basic issues for analysis of variance discussed in Jaccard and Guilamo-Ramos (2002). These include (a) using confidence intervals, (b) asserting group equivalence after a nonsignificant result, (c) use of magnitude estimation approaches, (d) sample size and power considerations, (e) outlier analysis, (f) violations of assumptions, and (g) missing data. Suggestions are offered for analytic practices in each of these domains.

Adolescent↗

PubMed2025

APAV: An advanced pangenome analysis and visualization toolkit.

Traditional pangenome analysis focuses on gene presence/absence variations (gene PAVs). However, the current methods for gene PAV analysis are insensitive to detect small but valuable mutations within gene regions, and they overlook variations in intergenic regions. Additionally, the visual inspection of PAVs is an important but time-consuming step for pangenome analysis and result interpretation. To address these issues, we present APAV, an advanced toolkit designed for comprehensive PAV analysis and visualization. It integrates gene element-level PAV analysis and provides PAV analysis for arbitrary given regions in a genome. The resulted PAV profile can be visualized and investigated interactively with reports in HTML format, enabling researchers to conveniently verify sequencing read depth, target region coverage, and intervals of absence for each PAV. Furthermore, APAV offers various subsequent analysis and visualization functions based on the PAV profile table, including basic statistics, sample clustering, genome size estimation, and phenotype association analysis. We demonstrated the capability of APAV with pangenome analysis of tumor genomes and rice genomes. Performing PAV analysis at the element level not only provides more accurate information about the variations but also uncovers a larger number of variations for the phenotype-genotype association studies. In the rice genome analysis, we identified over twenty thousand distributed genes and more than fifty thousand distributed genetic elements. In the tumor genome analysis, element-level analysis revealed approximately three times as many phenotype-related genes as gene-level analysis. This indicates that altering the PAV unit from genes to smaller segments or elements can lead to more biological insights.

Software↗

PubMed2004

A prospective randomized comparison of train-of-four monitoring and clinical assessment during continuous ICU cisatracurium paralysis.

STUDY PURPOSE: Train-of-four (TOF) monitoring is often recommended during the continuous use of neuromuscular blockade (NMB) [paralysis] in the ICU. Prior study results are conflicting regarding the benefits of TOF monitoring. DESIGN: Thirty patients in the medical ICU were randomized to TOF monitoring (n = 16) or to clinical assessment (n = 14) during continuous cisatracurium infusion. TOF monitoring was done at least every 4 h, with the goal being maintenance of one to two twitches. Statistical analysis was performed by two-tailed, unpaired t test (with Bonferroni correction for multiple comparisons), chi(2), and Fisher exact test, with p < 0.05 considered significant. Given a power of 80%, and the variance seen in the two groups, we estimate that the sample size used is sufficient to detect a change of > or = 60 min between groups for recovery time. RESULTS: The mean recovery time after cessation of paralytics was no different between TOF and clinical assessment (45 +/- 7 min vs 38 +/- 10 min, respectively [mean +/- SEM]). No differences were noted for mean APACHE (acute physiology and chronic health evaluation) II entry scores, glomerular filtration rates, or use of corticosteroids. No significant differences were noted between TOF monitoring and clinical assessment in mean total paralysis time (4,118 +/- 1,012 min vs 3,188 +/- 705 min, respectively), mean total cisatracurium dose (920 +/- 325 mg vs 715 +/- 167 mg), or dosage (2.3 +/- 0.2 microg/kg/min vs 2.9 +/- 0.2 microg/kg/min). CONCLUSIONS: TOF monitoring does not lead to improved recovery time or lower cisatracurium dosing compared with monitoring by clinical assessment. We conclude that TOF monitoring is unnecessary, and careful titration of the neuromuscular blocking agent by clinical assessment alone is sufficient in patients undergoing continuous cisatracurium NMB.

Atracurium↗

PubMed2006

Multivariate probability-based detection of drug-induced hepatic signals.

Clinical signal detection of drug-induced hepatic effects is a very inexact science. Ordinary clinical laboratory tests are the primary biomarkers for liver changes. Heuristic rules have been developed by clinicians for diagnosing liver disease and monitoring these changes. These are based on laboratory reference limits, which are also largely heuristic. This article reviews some of the statistical characteristics of univariate reference limits and shows how they can and should be extended to multivariate reference regions. For instance, in the univariate approach, the probability of a false positive cannot be specified and grows with increasing numbers of analytes evaluated. However, accurate reference regions require very large samples from reference populations. Although the uniformly minimum variance unbiased estimator can greatly improve the mean-squared-error efficiency relative to a maximum likelihood estimator, it still requires tens of thousands of reference samples to estimate the 95% reference region for 20 analytes to an order of 95 +/- 1%, for example. Methods for constructing the elliptical reference region estimators and for sample size determination are provided. It is not feasible for small laboratories to make these calculations unless more rigorous methods of standardisation can be imposed and data merged across institutions. Large healthcare systems with electronic medical records and large pharmaceutical companies singly or in collaboration could generate sufficient sample sizes for accurate reference regions if techniques to make inter-laboratory results comparable are implemented. Exiting a reference region, whether population-based or individualised, can only tell you when the patient has changed from steady state. The region into which the patient's results enter and dynamics of this change are likely to contain considerable biological information. An example of this is Hy's rule. As the number of new, expensive biomarkers grows, it may be more cost-effective to find better ways to use the data we already collect, using the new biomarkers for validation. Mathematics and computers can help do this.

Chemical and Drug Induced Liver Injury↗

PubMed2002

Otoacoustic emissions in the general adult population of Nord-Trøndelag, Norway: I. Distributions by age, gender, and ear side.

Transient evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs) are described as a function of age, gender and ear side in an unscreened adult population of 6415 subjects comprising a subsample of the 51975 subjects from the Nord-Trøndelag Hearing Loss Study. While most descriptions of OAEs are from samples selected based on hearing threshold, the present sample is from a less selected general population. The OAEs were recorded as a part of the programme of a general health screening. The large sample size provided accurate estimations of mean values. TEOAEs were analysed at 1, 2 and 4 kHz. DPOAEs were measured with f2 frequencies of 2, 3, 4, 6, and 8 kHz. Signs of bimodality were seen in the OAE density distributions of the > or = 45-year age group. The OAEs declined as a function of age, with the steepest gradient between 30 and 65 years. OAEs were generally higher in females than in males and in right ears than in left ears. Controlling for pure-tone thresholds reduced some of the effects of age, gender and ear side.

Adult↗

PubMed1976

A comparison of iron bioassay diets.

Two broiler chick experiments wer conducted to evaluate four basal diets for iron bioassay suitability. The test basal diets, identified according to their principal ingredients and iron content, were: (1) starch-skim milk - 15 p.p.m., (2) degerminated corn-skin milk - 18 p.p.m. (3) degermianted corn-fish meal-isolated soy - 45 p.p.m., and (4) degermianted corn-fish meal-dehulled soy - 59p.p.m. Significant differences between an iron source with known low availability (ferric oxide) and a highly available iron source (ferrous sulfate) were not detected with the degerminated corn-fish meal-isolated soy or the degerminated corn-fish meal-dehulled soy diets. Likewise, there were no significant differences found between supplemental iron levels, 10 and 20 p.p.m. The corn-skim milk and starch-skim milk diets were both found to be satisfactory for iron bioassays. However, the sample size needed to estimate the population mean was almost twice as great for the starch-skim milk fed groups, than was needed for the corn-skim milk fed groups which indicates the corn-skim milk diet obtained greater sensitivity in testing iron sources and levels. Mortality was excessively high in the starch-skim milk fed group. Ferrous sulfate was superior to ferric oxide as a source of iron.

Animals↗

PubMed1998

Response time distributions in multidimensional perceptual categorization.

Three speeded categorization experiments were conducted using separable dimension stimuli. The form of the category boundary was manipulated across experiments, and the distance from category exemplars to the category boundary was manipulated within each experiment. Observers completed several sessions in each experiment, yielding 300-400 repetitions of each stimulus. The large sample sizes permitted accurate estimates of the response time (RT) distributions and RT hazard functions. Analyses of these data indicated: (1) RT was faster for stimuli farther from the category boundary, and this stochastic dominance held at the level of the RT distributions; (2) RT was invariant for all stimuli the same distance from the category boundary; (3) when task difficulty was high, errors were slower than correct responses, whereas this difference disappeared when difficulty was low; (4) small, consistent response biases appeared to have a large effect on the relation between correct and error RT; (5) the shape of the RT hazard function was qualitatively affected by distance to the category boundary. These data establish a rich set of empirical constraints for testing developing models of categorization RT.

Humans↗

PubMed2001

Prevalence of known diabetes in Chennai City.

AIM: To determine prevalence of known diabetes in those more than 20 years of age in Chennai city. METHODOLOGY: Urban population was selected for the survey. Assuming the prevalence of known diabetes as 5.0% in those aged > 20 years, the cluster sample size calculated to estimate it with 95% CI and +/- 10% precision, was 25800 individuals of all ages. This population obtained from 200 households in each of 30 randomly selected corporation divisions of the city, was surveyed by social workers by house to house enquiry. General information and health status of every member of the household were recorded on prescribed forms. This survey was conducted during January-July, 1998. RESULTS: Among 26,066 individuals of all ages 779 had known diabetes and 99.4% of them had type 2 diabetes. The prevalence of known diabetes was 2.9% for all ages and both sexes combined. Crude and age-standardized prevalence was 4.9% (95% CI 4.6-5.2) for those aged > 20 years. The standardized prevalence was 10.5% (95% CI 9.8 - 11.2) in those aged > or = 40 years. The prevalence was significantly high (P < 0.05) in females. CONCLUSION: The prevalence of known diabetes was low in total population but increased in those aged > 20 and further increased in those aged > or = 40 years. The causes for high prevalence in > or = 40 year age group needs to be explored in this population.

Adolescent↗

PubMed1991

The neurons of the retinal ganglion cell layer of the guinea pig: quantitative analysis of their distribution and size.

1. The topographical distribution of ganglion cells and displaced amacrine cells in the guinea pig retina is described. 2. Neurons were counted in the ganglion cell layer of retinal whole mounts stained by the method of Nissl or retrogradely labeled with horseradish peroxidase. Neuronal soma size was estimated from samples taken from different retinal regions. 3. We estimate that a total of 295,000 neurons comprise the guinea pig ganglion cell layer and they consist of 159,000 ganglion cells and 136,000 displaced amacrine cells. 4. The visual streak is poorly differentiated. Ganglion cell density reaches a peak of 2,272 cells/mm2 in a temporal expansion of the visual streak, 4-5 mm toward the optic disk. The visual streak temporal expansion may represent the analogue of the area centralis for this species. The ventral hemi-retina has a higher ganglion cell density than the dorsal hemi-retina. The displaced amacrine cells are more uniformly distributed than the ganglion cells. 5. The present paper provides relevant data concerning the number and distribution of the neurons of the retinal ganglion cell which were not available or were very contradictory in the literature.

Animals↗

PubMed1989

[Relation between salt intake and blood pressure].

We investigated in a population group of 78 middle-aged men urinary sodium and potassium excretion per 24 hours under normal living conditions and the relationship to blood pressure. The mean urinary Na excretion in 24 hours was 241.3 mmol which corresponded to an intake of 14 g NaCl per day. The maximum NaCl consumption was as high as 30 g/day. The urinary Na excretion correlated in a linear fashion with the K excretion but not with the blood pressure. The blood pressure in the investigated group correlated with age, body mass index (kg/m2) and serum creatinine level. The body mass index and serum creatinine participated significantly in the blood pressure level, when multiple linear regression was used, where the urinary Na and K excretion per 24 hours were insignificant factors. In the investigated group a direct correlation of Na intake and blood pressure was not found, the investigation provided, however, information on the variability of urinary Na and K excretion/24 hours in the population and enables to estimate the necessary sample size to resolve this problem.

Adult↗

PubMed1994

Preparations for AIDS vaccine trials. Retention, behavior change, and HIV-seroconversion among injecting drug users (IDUs) and sexual partners of IDUs.

The likelihood that subjects in human immunodeficiency virus (HIV) vaccine efficacy trials will alter their behavioral risks for HIV infection over time must be considered in evaluating the feasibility of such trials and in estimating the necessary sample sizes to be enrolled. Potential subjects for future vaccine efficacy trials include injecting drug users (IDUs) and others who may be difficult to retain in studies and who may alter HIV-risk-related behaviors substantially over time. We have investigated behavior change, retention, and HIV seroconversion among 577 New York City resident IDUs and sexual partners of IDUs enlisted between July 1 and December 31, 1992. We attempted to see all subjects every 3 months for interviews, blood donation and HIV testing. We were able to retain 68% of subjects in the study through the third scheduled recall at 7.5-10.5 months after enlistment. HIV seroconversion through March 1, 1994, was 1.33/100 person-years at risk. There was a significant inverse relationship between HIV seroconversion and retention at the 9-month recall after adjusting for age, gender, and the amount of locator information provided by subjects at enlistment. Among subjects seen at each of the scheduled visits at 3, 6, and 9 months after enrollment, modest but statistically significant behavior changes that reduced risk were observed in self-reported drug injection frequency, heroin injection frequency, sexual contact with IDUs, and sharing of needles/syringes. The magnitude of these changes in risk, however, was small and may be transient. The behavior changes observed to date do not appear to be large enough to substantially alter calculations of sample sizes needed in future HIV vaccine efficacy trials.

AIDS Vaccines↗