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At least 1,063 records · Page 59Linked to original sources
PubMed2003

Using principal component analysis to monitor spatial and temporal changes in water quality.

Chemical, biological and physical data monitored at 12 locations along the Passaic River, New Jersey, during the year 1998 are analyzed. Principal component analysis (PCA) was used: (i) to extract the factors associated with the hydrochemistry variability; (ii) to obtain the spatial and temporal changes in the water quality. Solute content, temperature, nutrients and organics were the main patterns extracted. The spatial analysis isolated two stations showing a possible point or non-point source of pollution. This study shows the importance of environmental monitoring associated with simple but powerful statistics to better understand a complex water system.

Environmental Monitoring↗
PubMedDate not supplied

Statistical reanalysis of four recent randomized trials of acupuncture for pain using analysis of covariance.

OBJECTIVES: Acupuncture has been promoted for the treatment of chronic pain. Though many randomized trials have been conducted, these have been criticized for deficiencies of methodology, acupuncture technique, and sample size. Somewhat less emphasis has been placed on methods of statistical analysis. This paper describes 4 recent randomized trials of acupuncture for musculoskeletal or headache pain. Each trial used statistical methods that did not adjust for baseline pain scores and were thus of suboptimal power. The objective of this study is to reanalyze the trials using analysis of covariance (ANCOVA). METHODS: Raw data for the 4 trials were obtained from the original authors. Data were reanalyzed by ANCOVA. RESULTS: For 2 trials--acupuncture versus placebo for chronic headache and acupuncture versus transcutaneous electric nerve stimulation for back pain--reanalysis did not change the conclusion of no difference between groups, but showed that clinically significant differences between groups could not ruled out. Reanalysis of a trial of acupuncture versus placebo for shoulder pain slightly strengthened the evidence of acupuncture effectiveness. Reanalysis of the fourth trial, which compared acupuncture to placebo acupuncture and massage for neck pain, reversed the results of the original paper: reanalysis found acupuncture to be effective and that its effectiveness could not be ascribed to a placebo effect. DISCUSSION: Future trials of acupuncture and other modalities for pain should use efficient statistical methods. ANCOVA is more efficient than unadjusted analysis where used appropriately.

Acupuncture↗
PubMed1991

Electroretinogram b-wave implicit time and b/a wave ratio as a function of intensity in central retinal vein occlusion.

The ability of electroretinogram (ERG) b-wave implicit time and b/a wave ratio to predict iris neovascular response was analyzed as a function of stimulus intensity over a 3.6 log unit intensity range in 39 patients with central retinal vein occlusion (CRVO). Predictive power for CRVO patients was evaluated using ROC area at intensities of 1.23, 1.83, 2.43, and 3.03 effective log quanta/rod, where reliable data for both parameters were obtainable from most patients. The relative predictive power of b-wave implicit time and b/a wave ratio were shown to vary with stimulus intensity. The predictive power of b-wave implicit time, as measured by ROC area, declined to below significance at high intensity (above 1.83 log quanta/rod), while b/a wave ratio performed best at middle intensities (1.83 and 2.43 log quanta/rod) and not as well at high and low intensities. Further analysis of statistical behavior of both ERG parameters was obtained from the t statistic. Insight into the mechanism influencing predictive power of b-wave implicit time was derived from measurements on normal adults and CRVO patients with response data taken at high intensities. These results suggest that an optimal stimulus intensity range can be found for these ERG parameters in the evaluation of CRVO.

Aged↗
PubMed2007

Obesity and the risk of epithelial ovarian cancer: a systematic review and meta-analysis.

Obesity is a risk factor for several hormone-related cancers but evidence for an effect on risk of epithelial ovarian cancer remains inconclusive. Many studies evaluating this association have had insufficient statistical power to detect modest effects, particularly for histological subtypes of ovarian cancer. We have therefore assembled the published evidence on obesity and ovarian cancer in a systematic literature review and meta-analysis. We identified eligible studies using Medline and manual review of retrieved references, and included all population-based studies that assessed the association between overweight, body mass index (BMI25-29.9) and obesity (BMI30) and histologically confirmed ovarian cancer. Meta-analysis was restricted to those studies that expressed effect as an odds ratio (OR), risk ratio, or standardised incidence ratio and 95% confidence interval (CI). We identified 28 eligible studies, of which 16 on adult obesity and 9 on obesity in early adulthood were suitable for meta-analysis. Overall, 24 of 28 studies reported a positive association between obesity and ovarian cancer, and in 10 this reached statistical significance. The pooled effect estimate for adult obesity was 1.3 (95%CI1.1-1.5) with a smaller increased risk for overweight (OR1.2;95%CI1.0-1.3). The pooled OR was stronger among case-control studies (OR=1.5) than cohort studies (OR=1.1). Overweight/obesity in early adulthood was also associated with an increased risk of ovarian cancer. There was no evidence that the association varied for the different histological subtypes of ovarian cancer. Ovarian cancer should be added to the list of cancers likely to be related to obesity.

Adolescent↗
PubMed1999

Optimal experimental design for event-related fMRI.

An important challenge in the design and analysis of event-related or single-trial functional magnetic resonance imaging (fMRI) experiments is to optimize statistical efficiency, i.e., the accuracy with which the event-related hemodynamic response to different stimuli can be estimated for a given amount of imaging time. Several studies have suggested that using a fixed inter-stimulus-interval (ISI) of at least 15 sec results in optimal statistical efficiency or power and that using shorter ISIs results in a severe loss of power. In contrast, recent studies have demonstrated the feasibility of using ISIs as short as 500 ms while still maintaining considerable efficiency or power. Here, we attempt to resolve this apparent contradiction by a quantitative analysis of the relative efficiency afforded by different event-related experimental designs. This analysis shows that statistical efficiency falls off dramatically as the ISI gets sufficiently short, if the ISI is kept fixed for all trials. However, if the ISI is properly jittered or randomized from trial to trial, the efficiency improves monotonically with decreasing mean ISI. Importantly, the efficiency afforded by such variable ISI designs can be more than 10 times greater than that which can be achieved by fixed ISI designs. These results further demonstrate the feasibility of using identical experimental designs with fMRI and electro-/magnetoencephalography (EEG/MEG) without sacrificing statistical power or efficiency of either technique, thereby facilitating comparison and integration across imaging modalities.

Hemodynamics↗
PubMed1998

People and eyes: statistical approaches in ophthalmology.

In conclusion, when an observation by its nature involves two eyes, as for blindness, statistical analyses should be conducted on individuals rather than eyes and between eye correlation is not a problem. In other circumstances, if information on only one eye per individual is used in the analysis there is a potential "waste" of information leading to less precise estimates of effect and less power. In addition, bias may be introduced into a study if there is non-random selection of the eye for inclusion in the analysis. The use of an overall summary of ocular findings for an individual may result in "wastage" of information in a similar fashion to the use of only one eye per individual. On the other hand, an analysis of individual eyes with no allowance made for between eye correlation may result in falsely narrow confidence intervals around estimates of effect. Between eyes correlation may be assessed empirically using the kappa statistic or similar means. If between eye correlation is substantial, statistical techniques exist which can utilise all available data while allowing for the correlation. In some circumstances a powerful design may be to use the fellow eye as a "control". Two conclusions may be drawn from this review of analytical approaches to the analysis of clinical data in the BJO. Firstly, the analytical approaches employed in many studies fail to use all the data available. In other words the analysis is less than "optimal". Secondly, in a proportion of studies, inappropriate statistical methods are used which may lead the investigator to draw inappropriate conclusions. In other words, the analysis is invalid. Ophthalmic data, by their very nature, present particular statistical challenges. We emphasise the need to involve appropriate statistical expertise in the design and analysis of ophthalmic studies.

Bias↗
PubMed2003

Age and anesthetic effects on murine electrocardiography.

Murine models offer potential insights regarding human cardiac disease, but efficient and reliable methods for phenotype evaluation are necessary. We employed non-invasive electrocardiography (ECG) in mice, investigating statistical reliability of these parameters with respect to anesthetic and animal age. Mice (C57BL/6, 8 or 48 weeks) were anesthetized by ketamine/xylazine (K/X, 80/10 mg/kg ip) or by inhalation anesthetic (halothane, HAL; sevoflurane, SEV) and 6 lead ECGs were recorded. P wave duration and QT interval was significantly prolonged with K/X compared to HAL and SEV, indicating slowed atrial and ventricular conduction. P-R interval (atrio-ventricular conduction) was significantly increased in aged mice under all anesthetics. Heart rate was inversely correlated to QT interval and P wave duration. We also detected significant age effects with respect to optimal approaches for QT interval corrections. Power analysis showed 4-fold higher number of mice/group, were required for K/X, to achieve identical statistical sensitivity. These data demonstrate the importance of anesthetic selection for relevant and reliable ECG analysis in mice and illustrate the selective influences of anesthetics and age on cardiac conductance in this species.

Aging↗
PubMed1978

On data and methods in investigations on parental-age effects. Comments on a paper by J. D. Erickson.

An analysis of the NIS data used by Erickson (1977) has revealed that this data contains too few Down's syndrome cases with older fathers. Thus the data is less suited for an investigation of a possible paternal age effect. In addition, the statistical tests used by Erickson have low power, so that they are unable to detect a moderate paternal-age effect. Our analysis has demonstrated that discussions on paternal-age effects and similar problems should be based on high-quality data. The investigation is better based on a small high-quality material than on a large one with serious underascertainment. In the latter case one has to be extremely careful because the missing observations nearly always have common characteristics which may cause serious bias of relevant kinds.

Adult↗
PubMed1998

Précis of statistical significance: rationale, validity, and utility.

The null-hypothesis significance-test procedure (NHSTP) is defended in the context of the theory-corroboration experiment, as well as the following contrasts: (a) substantive hypotheses versus statistical hypotheses, (b) theory corroboration versus statistical hypothesis testing, (c) theoretical inference versus statistical decision, (d) experiments versus nonexperimental studies, and (e) theory corroboration versus treatment assessment. The null hypothesis can be true because it is the hypothesis that errors are randomly distributed in data. Moreover, the null hypothesis is never used as a categorical proposition. Statistical significance means only that chance influences can be excluded as an explanation of data; it does not identify the nonchance factor responsible. The experimental conclusion is drawn with the inductive principle underlying the experimental design. A chain of deductive arguments gives rise to the theoretical conclusion via the experimental conclusion. The anomalous relationship between statistical significance and the effect size often used to criticize NHSTP is more apparent than real. The absolute size of the effect is not an index of evidential support for the substantive hypothesis. Nor is the effect size, by itself, informative as to the practical importance of the research result. Being a conditional probability, statistical power cannot be the a priori probability of statistical significance. The validity of statistical power is debatable because statistical significance is determined with a single sampling distribution of the test statistic based on H0, whereas it takes two distributions to represent statistical power or effect size. Sample size should not be determined in the mechanical manner envisaged in power analysis. It is inappropriate to criticize NHSTP for nonstatistical reasons. At the same time, neither effect size, nor confidence interval estimate, nor posterior probability can be used to exclude chance as an explanation of data. Neither can any of them fulfill the nonstatistical functions expected of them by critics.

Reproducibility of Results↗
PubMed2001

Evaluation of the bioequivalence of highly-variable drugs and drug products.

PURPOSE: To establish procedures for the effective evaluation of bioequivalence (BE) for highly-variable drugs and drug products (HVD/P). METHODS: 2- and 4-period crossover BE studies with 24 subjects were simulated which generally assumed within-subject coefficients of variation of 40%. The relationship between the fraction of studies in which BE was accepted (the statistical power) and the ratio of geometric means (GMR) of the two formulations was evaluated for various methods of analysis. These included, primarily, scaled average BE (ABE), the corresponding approach of expanding BE limits (BEL), and, for comparison, unscaled ABE and scaled individual BE (IBE). RESULTS: Scaled ABE and expanding BEL showed very similar properties in both 2- and 4-period studies. They had steeper power curves than scaled IBE. Unscaled ABE had very low statistical power. The acceptance of BE by unscaled and scaled ABE and expanding BEL was almost independent of subject-by-formulation interaction and the ratio of within-subject variations of the two formulations. By contrast, the conclusions reached by scaled IBE were strongly affected by these parameters. CONCLUSIONS: Scaled ABE and expanding BEL evaluate BE effectively for HVD/P in both 2- and 4-period investigations. However, additional, useful information can be obtained from 4-period studies.

Analysis of Variance↗
PubMed1985

Case-control analysis of risk factors for presence of aortic stenosis in adults (age 50 years or older).

To analyze whether atherosclerotic risk factors, including systemic hypertension, an elevated serum cholesterol level, smoking and diabetes, were associated with the presence of aortic stenosis (AS) in adults, 105 adults who had AS without coronary artery disease (CAD) were compared with 110 control subjects who had other types of valvular disease, 170 control subjects who underwent catheterization and had neither valvular disease nor CAD, and 269 matched control subjects who underwent general surgery. When using each control group separately or in combination, no risk factor showed consistent evidence of a significant association with the development of AS. If the true magnitudes of these associations are of the order previously reported for the development of CAD, the power of our study for detecting statistical significance ranges from 56 to 99%. In a supplemental analysis, 45 cases with both AS and CAD did not have a higher prevalence of risk factors than cases without CAD. Although a weak association between atherosclerotic risk factors and AS cannot be excluded, any such association is unlikely to be as strong as for predicting CAD.

Aged↗
PubMed1993

The relationship between age, gender and cognitive performance in the very old: the effect of selective survival.

OBJECTIVE: To determine the prevalence of cognitive disability as a function of advanced age and gender in elderly nursing home and community-dwelling populations. Since cognitive dysfunction is associated with increased mortality, we hypothesized that selective survival results in a decreased prevalence of cognitive disability in the oldest old. DESIGN: Cohort study. An analysis of 6-month longitudinal data obtained from a national probability sample of older persons in 260 nursing homes (n = 1951) and 2-year-longitudinal data obtained from a sample of community-dwelling older persons (n = 2947). MEASURES: In the nursing home sample, the primary outcome measure was cognitive performance score. In the community sample, cognitive performance was determined using the results of three orientation questions and assessment of decision-making ability. Cognitive performance and subsequent survival, controlling for various disease states and demographic factors, were examined in three age cohorts of men and women (ages 65-79, 80-89, 90-99). RESULTS: In the nursing home sample, the cognitive performance of very old men (> or = 90 years) was better than that of younger men (aged 80-89 years, P < 0.05) and very old women (age > or = 90 years, P = 0.001). Among 80-89-year-olds with poor cognitive performance, the 6-month mortality rate was higher in men than in women (38% vs 19%, P = 0.001). However, the mortality rates of men and women with good cognitive performance were not statistically different in any age group. Proportional-hazards regression analysis demonstrated that poor cognitive performance remained a powerful predictor of death among men aged 80-89 years with a relative risk of 2.7 (95% Cl, 1.19-3.17; P = 0.0006) after controlling for covariates. Results from the community sample lent support to our findings: within each age group, mortality rates for men and women with intact cognitive performance were not statistically different. However, in the two older age groups, the mortality rates of subjects with impaired cognitive performance were significantly greater for men than for women (P < 0.01 for both age groups). CONCLUSIONS: Decreased cognitive performance is significantly associated with mortality among elderly men. Survival by men who have relatively intact cognitive function results in a population of oldest men, those aged 90-99 years, with cognitive performance scores better than younger men or similarly-aged women. The same selective survival phenomenon was not observed among women. Thus, there may be less cognitive disability among very old men than previously expected.

Age Factors↗
PubMed1999

The analysis of heart rate variability in unrestrained rats. Validation of method and results.

An experimental setting and software were developed to evaluate cardiac autonomic function in unrestrained rats. Subcutaneously implanted ECG electrodes and an indwelling venous catheter were tunneled to a tail cuff in five rats. The ECG was A/D converted at 1000 Hz. After peak detection, a time series of RR intervals was obtained. Programs for the analysis of heart rate variability (HRV) were implemented in LabVIEW. Statistical properties were determined in the time domain. After cubic spline function curve fitting, resampling at 0.1 s and test for stationarity, power spectral analysis was performed on sampled records of 30 min duration after applying a sliding Hanning window (Welch method: 256 points (duration 25.6 s), 50% overlap and 0.039 Hz resolution). Algorithms were tested with simulated signals consisting of isolated frequency components, which were retrieved at their exact locations. Physiological validation of the system was performed by, beta-adrenergic and cholinergic blockade and by forced breathing at a fixed rate. Measurements were performed on five unrestrained rats under basal conditions. Mean RR was 174.2 +/- 3.6 ms; S.D., 13.3 +/- 4.6 ms; rMSSD, 5.2 + /- 1.2 ms; pNN10, 3.5 +/- 1.9% and pNN5, 18.7 +/- 6.4%. Low (0.19-0.74 Hz) and high frequency (0.78-2.5 Hz) power were determined (and also percent of low to total and high to total): 18.42 +/- 10.74 ms2 (22.9 +/- 6.5%) and 15.66 +/- 5.56 ms2 (19.9 +/- 2.7%), and the ratio low/high: 1.16 +/- 0.39. In conclusion, HRV analysis programs were developed and thoroughly tested through simulations and in vivo, under basal conditions and after pharmacological blockades. Using this software, HRV data from unrestrained rats were obtained.

Animals↗
PubMedDate not supplied

Effect of age and repeated hyperbaric oxygen treatments on vagal tone.

OBJECTIVES: To evaluate the influence of repeated hyperbaric oxygen (HBO2) exposures and age on vagal response to hyperbaric oxygenation, and to evaluate the timing of changes in vagal activity during the treatments. STUDY DESIGN: Open, controlled, non-randomized study. METHODS: Heart rate variability of 23 patients with chronic osteomyelitis or radionecrosis of the jaw or reconstructive surgery of the facial region was studied during repeated treatments. During each treatment, the patients were exposed to HBO2 at 2.5 ATA and heart rate variability was measured using power spectral analysis before compression, three times at 2.5 ATA and during and after decompression. The patients were grouped according to age (Cut-off point 50 years). Statistical analysis was carried out using analysis of variance for repeated measurements. RESULTS: Repeated exposures did not change vagal response to hyperbaric oxygenation. Vagal activity measured by HF power increased significantly in both age groups during the HBO2 exposures but there were no significant difference between the groups in the response. However, the level of HF power was significantly higher in the subjects under 50 years old. Significant differences between consecutive measurements were related to pressure changes. CONCLUSIONS: Repeated therapeutic HBO2exposures are not causing permanent changes in vagal control of the heart. Vagal responsiveness to hyperbaric hyperoxia is preserved in advanced age.

Adult↗
PubMed2005

AUTOGSCAN: powerful tools for automated genome-wide linkage and linkage disequilibrium analysis.

Genome-wide linkage analysis using multiple traits and statistical software packages is a tedious process which requires a significant amount of manual file manipulation. Different linkage analysis programs require different input file formats, making the task of analyzing data with multiple methods even more time-consuming. We have developed a software tool, AUTOGSCAN, that automates file formatting, the running of statistical analyses, and the summarizing of resulting statistics for whole genome scans with a push of a button, using several independent, and often idiosyncratic, statistical software packages such as MERLIN, SOLAR and GENEHUNTER. We also describe a program, ANALYZE, designed to run qualitative linkage analysis with several different statistical strategies and programs to efficiently screen for linkage and linkage disequilibrium for a given discrete trait. The ANALYZE program can also be used by AUTOGSCAN in a genome-wide sense.

Genetic Linkage↗
PubMed2006

A meta-analysis of quantitative EEG power associated with attention-deficit hyperactivity disorder.

A meta-analysis was performed on quantitative EEG (QEEG) studies that evaluated attention-deficit hyperactivity disorder (ADHD) using the criteria of the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th edition). The nine eligible studies (N = 1498) observed QEEG traits of a theta power increase and a beta power decrease, summarized in the theta/beta ratio with a pooled effect size of 3.08 (95% confidence interval, 2.90, 3.26) for ADHD versus controls (normal children, adolescents, and adults). By statistical extrapolation, an effect size of 3.08 predicts a sensitivity and specificity of 94%, which is similar to previous results 86% to 90% sensitivity and 94% to 98% specificity. It is important to note that the controlled group studies were often with retrospectively set limits, and that in practice the sensitivity and specificity results would likely be more modest. The literature search also uncovered 32 pre-DSM-IV studies of ADHD and EEG power, and 29 of the 32 studies demonstrated results consistent with the meta-analysis. The meta-analytic results are also supported by the observation that the theta/beta ratio trait follows age-related changes in ADHD symptom presentation (Pearson correlation coefficient, 0.996, P = 0.004). In conclusion, this meta-analysis supports that a theta/beta ratio increase is a commonly observed trait in ADHD relative to normal controls. Because it is known that the theta/beta ratio trait may arise with other conditions, a prospective study covering differential diagnosis would be required to determine generalizability to clinical applications. Standardization of the QEEG technique is also needed, specifically with control of mental state, drowsiness, and medication.

Adolescent↗
PubMed2006

Current perspectives on the genetic analysis of autism.

Although no definitive genetic mutations leading to autism susceptibility have been established, the field has many new resources to tackle this difficult problem. Numbers of families at many research sites are now large, and new collaborations among these groups will allow for collections of subjects with enough statistical power to detect relatively small gene effects. New technological advances in genotyping will allow for more fine-grained genetic analysis, and more sophisticated techniques have been developed to address the vast amounts of data acquired. Researchers have also begun to focus on intermediate phenotypes associated with autism, such as elevated serotonin, increased head circumference, social difficulties, or language impairment or delay. These phenotypes may help to stratify affected cases into more genetically homogeneous subgroups, and may also occur in their clinically unaffected relatives. The study of intermediate phenotypes may allow investigators to find common gene variants that lead to autism susceptibility. Here we discuss the major intermediate phenotypes, and give an overview of current genetic analysis techniques.

Autistic Disorder↗