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PubMed1996

Advantages and disadvantages of the meta-analysis approach.

UNLABELLED: ADVANTAGES OF META-ANALYSIS: Literature reviews have traditionally been largely narrative. Meta-analysis now offers the opportunity to critically evaluate and statistically combine results of comparable studies or trials. Its major purposes are to increase the numbers of observations and the statistical power, and to improve the estimates of the effect size of an intervention or an association. METHODS: There is, as yet, no unanimously accepted strategy for performing a meta-analysis but researchers agree that each meta-analysis should be conducted like a scientific experiment and begin with a protocol, which clearly states its aim and methodology. Meta-analysts disagree on the criteria for inclusion or exclusion of primary studies, with relation to publication status, comparability and required scientific quality, but sensitivity analyses make it possible to assess the impact of various selection criteria on the results. Several statistical methods have been developed to analyse data extracted from the literature; more recently, meta-analyses have also been performed on individual subject data. CONCLUSIONS: Meta-analysis is superior to narrative reports for systematic reviews of the literature, but its quantitative results should be interpreted with caution even when the analysis is performed according to rigorous rules.

Humans↗
PubMed2005

Social functioning and personality of subjects at familial risk for affective disorder.

BACKGROUND: Particular patterns of personality (e.g., neuroticism, obsessionality) and difficulties in various social roles have been found to be associated with unipolar depression. Interpersonal and instrumental difficulties of depressives can be understood either as a risk factor, or as a consequence caused by the disorder itself. Concerning patients with bipolar disorder, there is some evidence that their premorbid level of occupational and educational achievement is often superior when compared to the premorbid functioning of patients with unipolar depression. METHODS: Personality features and the level of social functioning of 114 high-risk subjects (healthy first-degree relatives of patients suffering from an affective disorder) have been investigated using self- and expert-ratings. Sixty-three subjects without a personal and family history of psychiatric disorder served as the reference group. RESULTS: Relatives of melancholic depressives described themselves as more neurotic than controls but proved to be inconspicuous regarding their role functioning. Relatives of bipolar I patients were more strongly oriented toward social norms, and their instrumental role functioning was superior to that of controls. Neuroticism was strongly associated with depressive symptoms. LIMITATION: The statistical power of our data is sufficient to detect medium effect sizes but is insufficient for identifying small group differences. CONCLUSION: Whether these discriminating personality features and other variables (not characterising the high-risk group (HRG) as a whole) act as true vulnerability factor have to be clarified by a follow-up investigation.

Adolescent↗
PubMed1999

Variation over time of the effects of prognostic factors in a population-based study of colon cancer: comparison of statistical models.

The authors compare the performance of different regression models for censored survival data in modeling the impact of prognostic factors on all-cause mortality in colon cancer. The data were for 1,951 patients, who were diagnosed in 1977-1991, recorded by the Registry of Digestive Tumors of Côte d'Or, France, and followed for up to 15 years. Models include the Cox proportional hazards model and its three generalizations that allow for hazard ratio to change over time: 1) the piecewise model where hazard ratio is a step function; 2) the model with interaction between a predictor and a parametric function of time; and 3) the non-parametric regression spline model. Results illustrate the importance of accounting for non-proportionality of hazards, and some advantages of flexible non-parametric modeling of time-dependent effects. The authors provide empirical evidence for the dependence of the results of piecewise and parametric models on arbitrary a priori choices, regarding the number of time intervals and specific parametric function, which may lead to biased estimates and low statistical power. The authors demonstrate that a single, a priori selected spline model recovers a variety of patterns of changes in hazard ratio and fits better than other models, especially when the changes are non-monotonic, as in the case of cancer stages.

Aged↗
PubMed2002

No effect of chinese acupuncture on isocapnic hyperventilation with cold air in asthmatics, measured with impulse oscillometry.

The cost to society and the individual of treating asthma has been increasing in developed countries. This has given rise to studies of the efficacy of complementary treatments. The aim of this study was to evaluate the efficacy of traditional Chinese Acupuncture in patients with mild asthma. The method used for evaluation of efficacy was total airway resistance at 5Hz (R5) as measured by impulse oscillometry (IOS)--a forced oscillation technique, at baseline and after a bronchial challenge with voluntary isocapnic hyperventilation of cold air (IHCA). The study was a parallel group randomised placebo controlled trial with evaluator blinding. Twenty-seven asthmatics were recruited and 24 completed the study, 10 of them received acupuncture and 14 received a placebo treatment (mock-TENS). Treatment continued for 15 weeks, and efficacy was tested two weeks following the last treatment. Randomisation resulted in female over representation in the acupuncture group, but lung-function and bronchial responsiveness to IHCA were comparable in the two populations before the start of treatment (p>0.05 vs. p > 0.05). There were no statistically significant effects of the treatment before (p > 0.05) or after IHCA (p > 0.05) in either of the groups. The statistical power of the study to show a clinically relevant difference in bronchial responsiveness to IHCA after treatment was near 80%. We conclude that there were no significant effects of traditional Chinese Acupuncture on airway status in our patients with asthma.

Acupuncture Therapy↗
PubMed2006

Issues in multi-item scale testing and development using structural equation models.

Employing a structural equation model to evaluate a measurement scale can be challenging, especially for a multidimensional scale that contains many items. We describe two issues that can contribute to the poor fit of such models: the statistical power associated with the test of a large measurement scale; and the degree of correlation between items and factors within the scale. These issues are not well understood, so our purpose is to explain them at an applied level, clarify their practical implications for tests of measurement scales and other large structural equation models, and discuss potential strategies for addressing them.

Data Interpretation, Statistical↗
PubMed1990

How many patients are necessary to assess test performance?

Test performance characteristics are important in assessing the clinical usefulness of laboratory tests and serve as a basis for comparing one test to another. Statistical comparisons of performance characteristics are meaningful only when they can detect medically important differences; that is, when they provide adequate statistical power. This requires choosing the appropriate sample size in determining the performance characteristics of interest. Using standard formulas, we designed tables that provide such sample size requirements. Example problems of sample size determination in laboratory test comparisons are given. Used appropriately, this approach should result in better studies of laboratory tests and fewer meaningless negative studies.

Clinical Laboratory Techniques↗
PubMedDate not supplied

Incorporating predictions of individual patient risk in clinical trials.

A risk prediction model is a statistical technique that gives a predicted probability of a certain event for an individual patient. Prediction models outperform the traditional risk classification systems that work by assigning patients into risk groups based on the presence or absence of particular risk factors, such as stage of disease. As such, risk prediction models have a number of important possible uses in clinical trials. For Phase II studies, prediction models can help adjust comparisons with historical control groups for differences in case mix. For Phase III studies, prediction models can ensure that accrued patients are at sufficiently high risk. This improves statistical power and avoids unethical inclusion of low-risk patients. We also propose that prediction models could potentially be used for applying the results of Phase III trials to individual patients. Clinical decisions could be informed by individualized estimates of treatment benefit, rather than by average treatment effects.

Clinical Trials, Phase III as Topic↗
PubMed1995

When is it worth measuring a covariate in a randomized clinical trial?

In a randomized clinical trial, an experimenter can increase statistical power by including a covariate (e.g., a pretest). This will generally reduce the total number of participants needed to achieve a specified level of power. However, it will also increase the cost per participant. Thus, the question arises, "When do the savings incurred by needing fewer participants exceed the costs incurred by measuring each participant on the covariate?" A simple closed form expression is derived that applied researchers can use in the design phase of studies to answer this question.

Adult↗
PubMed1988

General statistical design considerations of randomized clinical trials.

Randomized clinical trials are the most objective method for evaluating new therapies, but they are subject to the same biases as nonrandomized studies unless the principles of statistical design are observed at the planning stage. Estimation of sample size also requires early careful consideration, since studies of inadequate size will not have sufficient statistical power to detect meaningful treatment differences. For ethical reasons, interim data monitoring procedures should be used to detect early treatment responses that may lead to alteration or interruption of the planned study to give patients early benefit from a superior treatment or diminish their risk from ineffective or harmful treatment. Additional important aspects of clinical trial design that were not addressed in this report include: definition of study objectives and endpoints, description of data to be collected, details of the treatment regimens, informed consent and plans for data analysis. The science of clinical trial design is complex; only some of the key statistical issues have been addressed briefly in this report.

Clinical Trials as Topic↗
PubMed2002

Meta-analysis of genetic-linkage analysis of quantitative-trait loci.

Meta-analysis is an important tool in linkage analysis. The pooling of results across primary linkage studies allows greater statistical power to detect quantitative-trait loci (QTLs) and more-precise estimation of their genetic effects and, hence, yields conclusions that are stronger relative to those of individual studies. Previous methods for the meta-analysis of linkage studies have been proposed, and, although some methods address the problem of between-study heterogeneity, most methods still require linkage analysis at the same marker or set of markers across studies, whereas others do not result in an estimate of genetic variance. In this study, we present a meta-analytic procedure to evaluate evidence from several studies that report Haseman-Elston statistics for linkage to a QTL at multiple, possibly distinct, markers on a chromosome. This technique accounts for between-study heterogeneity and estimates both the location of the QTL and the magnitude of the genetic effect more precisely than does an individual study. We also provide standard errors for the genetic effect and for the location (in cM) of the QTL, using a resampling method. The approach can be applied under other conditions, provided that the various studies use the same linkage statistic.

Computer Simulation↗
PubMed2003

Ordered-subsets linkage analysis detects novel Alzheimer disease loci on chromosomes 2q34 and 15q22.

Alzheimer disease (AD) is a complex disorder characterized by a wide range, within and between families, of ages at onset of symptoms. Consideration of age at onset as a covariate in genetic-linkage studies may reduce genetic heterogeneity and increase statistical power. Ordered-subsets analysis includes continuous covariates in linkage analysis by rank ordering families by a covariate and summing LOD scores to find a subset giving a significantly increased LOD score relative to the overall sample. We have analyzed data from 336 markers in 437 multiplex (>/=2 sampled individuals with AD) families included in a recent genomic screen for AD loci. To identify genetic heterogeneity by age at onset, families were ordered by increasing and decreasing mean and minimum ages at onset. Chromosomewide significance of increases in the LOD score in subsets relative to the overall sample was assessed by permutation. A statistically significant increase in the nonparametric multipoint LOD score was observed on chromosome 2q34, with a peak LOD score of 3.2 at D2S2944 (P=.008) in 31 families with a minimum age at onset between 50 and 60 years. The LOD score in the chromosome 9p region previously linked to AD increased to 4.6 at D9S741 (P=.01) in 334 families with minimum age at onset between 60 and 75 years. LOD scores were also significantly increased on chromosome 15q22: a peak LOD score of 2.8 (P=.0004) was detected at D15S1507 (60 cM) in 38 families with minimum age at onset >/=79 years, and a peak LOD score of 3.1 (P=.0006) was obtained at D15S153 (62 cM) in 43 families with mean age at onset >80 years. Thirty-one families were contained in both 15q22 subsets, indicating that these results are likely detecting the same locus. There is little overlap in these subsets, underscoring the utility of age at onset as a marker of genetic heterogeneity. These results indicate that linkage to chromosome 9p is strongest in late-onset AD and that regions on chromosome 2q34 and 15q22 are linked to early-onset AD and very-late-onset AD, respectively.

Age of Onset↗
PubMed1993

Some developments on the affected-pedigree-member method of linkage analysis.

Some improvements are presented for the affected-pedigree-member method of linkage analysis, which is a generalization of the sib-pair method. The test statistic is extended to include contrasts between affected and unaffected pedigree members, so that it now utilizes marker information from all typed pedigree members rather than just the typed affected members. Computer simulation using a sample pedigree of 14 individuals shows that this modification can substantially increase statistical power where there is a direct association between marker variation and disease and where disease risk is elevated in carriers of the disease allele. Data on Huntington disease in 16 British families, which were analyzed previously using only the affected individuals, are reanalyzed with the unaffected individuals included. Strong rejection of the null hypothesis of no association between Huntington disease and the HindIII polymorphism is confirmed, but the particular families in which the association is significant differs from that obtained through an analysis based only on affected individuals and reflects more closely the results obtained from a lod-score analysis. The test statistic is also modified here to incorporate contrasts between individuals of zero kinship, if needed. This enables contrasts between individuals from different pedigrees, as well as contrasts involving individuals sampled from the general population, to be incorporated into the test of association. For population data, the methodology reduces to a type of contingency-table analysis, in which the rows of the table correspond to different marker-locus genotypes and in which the two columns categorize subjects into an "affected" group versus an "unaffected," or control, group. This aspect of the methodology is illustrated using two population data sets, the first relating APO-E genotype to the frequency of individuals undergoing maintenance hemodialysis and the second relating APO-B genotype to the frequency of coronary artery disease. The present methodology confirms the lack of association between marker and disease in the former data set and confirms the presence of association in the latter. Finally, the methodology is formulated here in terms of ordinary, multiperson kinship coefficients rather than in terms of the generalized kinship coefficients originally proposed. This greatly reduces the number of coefficients to be calculated, thereby enhancing the computational efficiency of the computer program.

Apolipoproteins B↗
PubMed1984

Sex in lateralized tachistoscopic word recognition.

Although a generalized sex difference in lateralization appears to be established, a review of the literature pertaining to lexical tachistoscopic tasks suggests a dissociation by method: females show reduced visual field asymmetries relative to males in lexical decision and naming, but not in word recognition. Here 14 recognition experiments from the author's laboratory are subjected to meta-analysis, and the literature review is confirmed. There is no sex difference is visual field asymmetry for the task, although an overall field difference is found and statistical power is high to find the interaction. Possible reasons for the discrepancy with lexical decision and naming findings are discussed. One possibility is that stress on reaction time in those tasks produces a complex interaction between sex, activation/arousal, and hemispheric differences, which is not found when a less speeded method is used.

Adult↗
PubMed2004

Sample size estimation: a glimpse beyond simple formulas.

Small increments in the complexity of clinical studies can readily take sample size estimation and statistical power analysis beyond the capabilities of simple mathematic formulas. In this article, the method of simulation is presented as a general technique with which sample size may be calculated for complex study designs. Applications of simulation for determining sample size requirements in studies involving correlated data and comparisons of receiver operating characteristic curves are discussed.

Clinical Trials as Topic↗
PubMed2006

Novel scaled bioequivalence limits with leveling-off properties.

PURPOSE: (1) To develop novel scaled bioequivalence (BE) limits with levelling-off properties based solely on variability considerations and (2) to evaluate their performance in comparison to the classic unscaled BE limits 0.80-1.25, the expanded BE limits 0.75-1.33 and the recently proposed Geometric Mean Ratio (GMR)-dependent scaled BE limits BELscW (Karalis et al., Eur. J. Pharm. Sci., 26:54-61, 2005). MATERIALS AND METHODS: Two model functions were used to ensure the gradual change of the BE limits from a starting value towards a predefined plateau value. Plots of the new BE limits and extreme GMR values ensuring BE as a function of the coefficient of variation (CV) were constructed. Two-period crossover BE studies with 12, 24, or 36 subjects were simulated assuming CV values from 10 to 60%. Power curves were constructed by recording the percentage of accepted BE studies as the true GMR was raised from 1.00 to 1.50. The percentage of the true GMR within the simulated BE limits vs. true GMR was used to evaluate the estimation accuracy of the scaled methods. RESULTS: Depending on the parameters' values of the model functions, the scaled BE limits exhibit different performance. Four new scaled BE limits, showing favourable performance for the evaluation of average BE are presented. At low variability levels two of the novel BE limits show similar performance to the 0.80-1.25 criterion, while the other two (as expected from their design) appear to be less permissive. At high CV values (30, 40%) all new BE limits exhibit much higher statistical power than the 0.80-1.25 criterion. They show almost identical behavior with the expanded 0.75-1.33 limits and appear to be less permissive than BELscW. Finally, the percentage of the true GMR within the simulated BE limits vs. true GMR shows a sharp decline. Due to the absence of the GMR factor in the model functions a more accurate estimation of the new scaled BE limits, compared to BELscW, is observed. CONCLUSIONS: The new scaled BE limits appear to be highly effective at all levels of variation investigated and present satisfactory estimation accuracy.

Data Interpretation, Statistical↗
PubMed2006

Chemometrics in monitoring spatial and temporal variations in drinking water quality.

This case study reports multivariate techniques applied for the evaluation of temporal/spatial variations and interpretation of monitoring data obtained by the determination of chloro/bromo disinfection by-products in drinking water at 12 locations in the Gdańsk area (Poland), over the period 1993-2000. The complex data matrix (1756 observations) was treated with various multivariate techniques. Cluster analysis (CA) was successful, yielding two different groups of similarity reflecting different types of drinking water supplied (surface and groundwater). The locations supplied in general with groundwater could be further classified into two subgroups, depending on whether the groundwater was mixed with surface water or not. Analysis of variance (ANOVA) was used to classify and thus confirm the groups found by means of cluster analysis and proved the existence of statistically significant differences between the concentration levels of CHCl3, CHBrCl2+C2HCl3, CHBr2Cl, and CH2Cl2 in the samples collected. Of all the variables evaluated, only three were characterized by statistically significant correlations (CHCl3, CHBrCl2+C2HCl3, CHBr2Cl). The analysis of correlation coefficients revealed that chloroform formed as the main chlorinated disinfection by-product and, furthermore, the natural presence of bromide in water (both ground and surface) results in the formation of brominated disinfection by-products (DBPs). Temporal variations of volatile organic chlorinated compounds (VOCls) were also evaluated by multidimensional ANOVA. Observation of temporal changes in the concentration of VOCls at the location supplied with both surface and groundwater reveals a steady improvement in drinking water quality. In general, the study shows the importance of drinking water monitoring in connection with simple but powerful statistical tools to better understand spatial and temporal variations in water quality.

Cluster Analysis↗
PubMed2000

Prognostic evaluation of primary non-small cell lung carcinoma patients using biological fluid variables. A systematic review.

We have systematically reviewed the biomedical literature to try to establish whether laboratory variables might give any additional prognostic information in non-small-cell lung cancer (NSCLC) patients independently of the usual radioclinical parameters. In each study, we acknowledged the independent prognostic value of a biological fluid variable if it had been demonstrated through a multivariate statistical analysis in which at least the following had been included: patient's weight loss, age, gender, performance status, histology, stage and extent of the disease. The clearest conclusion that can be derived from the 42 studies we reviewed is that it remains to be clearly demonstrated whether or not the "new" tests (tumour markers, p53 antibodies, etc.) are superior to the "old" tests (serum LDH, calcium, albumin or other proteins, blood cell counts, etc.), even though a number of studies did suggest that serum cyfra 21-1 has a pre-therapeutic prognostic significance in NSCLC. From the four studies in which the same powerful statistical methodologies were used (i.e. Cox models in association with RECPAM analysis), it could be derived that serum calcium and perhaps the blood neutrophil and lymphocyte counts might have independent pre-therapeutic prognostic significance in advanced NSCLC. Further studies are needed to demonstrate whether repeated measurements during therapeutic follow-up can bring any independent prognostic information. Provided that both laboratory and statistical expertise is clearly guaranteed in future primary studies published in this particular biomedical field, it might perhaps become possible to propose laboratory variables as additional prognostic parameters in NSCLC.

Biomarkers, Tumor↗
PubMed1996

Controlled clinical trials in cancer research.

Knowledge of important aspects of the design and analysis of clinical trials is essential to clinical researchers and readers of medical literature. A brief description of proper trial design, including the contents of a trial protocol, as well as different strategies to avoid bias, is given. The concept of p-values is explained, and some commonly used statistical analysis methods are mentioned. Statistical power is defined, and two useful formulas and examples of estimating sample size are presented. The correct interpretation of trial results is emphasized, and misinterpretations and errors that frequently occur are dealt with. Various issues regarding multiple significance testing, such as interim analyses, multiple endpoints, and subgroup analyses, are addressed.

Controlled Clinical Trials as Topic↗