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PubMed1994

Efficacy of new generation antidepressants: meta-analysis of imipramine-controlled studies.

When assessing the efficacy of a new antidepressant in comparison with a standard treatment, most clinical trials have come to the conclusion that the nullhypothesis (equal efficacy) cannot be rejected, and have not been reformulated with respect to (at least) equivalent studies. However, it cannot be concluded from this that the compared treatments have the same (or similar) efficacy, because in many of the studies the statistical power is not sufficient. Using the effect-size formula described by Glass et al. (1981), a meta-analysis were performed combining the results of comparative trials of maprotiline, mianserin, viloxazine, trazodone, nomifensine, fluvoxamine, and fluoxetine, performed according to similar objectives and designs (similar patient selection, double-blind, randomized, etc.) and with imipramine as reference compound. Together with the results of a former meta-analysis of amitriptyline-controlled studies (Möller and Haug, 1988) the present investigation indicates differences in efficacy, which in the case of most of the new generation antidepressants is similar to the reference compounds imipramine and amitriptyline.

Adolescent↗

PubMed2004

Phacoemulsification parameters: series 20000 Legacy Versus Legacy with AdvanTec software and NeoSoniX handpiece.

PURPOSE: To examine the differences in average phaco power and effective phaco time (EPT) and evaluate the clinical results with the standard Series 20000 Legacy system (Alcon) and the Legacy with AdvanTec software and the NeoSoniX handpiece (Alcon). SETTING: Department of Ophthalmology, University Hospital, Hradec Králové, Czech Republic. METHODS: The mean phaco power and EPT in 240 eyes of 240 consecutive patients having cataract surgery by a single surgeon using the standard Legacy 20000 system were retrospectively compared with results in 240 eyes of 240 consecutive patients operated on by the same surgeon using the Legacy with AdvanTec software and the NeoSoniX handpiece. Statistical analysis was performed using the Kruskal-Wallis 1-way analysis of variance. All chi-square (chi(2)) values are approximations. RESULTS: The EPT and mean phaco power were less in the AdvanTec-NeoSoniX group than in the standard Legacy 20000 group in all cases. The mean EPT was 56.9 seconds +/- 29.5 (SD) in the standard Legacy 20000 group and 4.2 +/- 3.8 seconds in the AdvanTec-NeoSoniX group. The mean phaco power was 19.2% +/- 6.2% and 5.1% +/- 2.5%, respectively. The difference between groups was statistically significant in EPT (age > or =90 years, chi(2) = 4.5, P =.034; age <90 years, chi(2)>57, P<.00005) and in mean phaco power (chi(2) = 4.58 and P =.032 and chi(2)>44 and P<.00005, respectively). No trace of corneal striae or edema was observed in 92% eyes on the first postoperative day. The best corrected visual acuity was 20/25 or better in 60% of cases. CONCLUSIONS: The Legacy system with AdvanTec software and the NeoSoniX handpiece significantly reduced the mean EPT and phaco power. This low-power technology minimizes intraoperative damage to ocular structures and maximizes the level and rapidity of visual rehabilitation.

Aged↗

PubMedDate not supplied

On combining dose-response data from epidemiological studies by meta-analysis.

Using data from a meta-analysis of the effects of oestrogen replacement therapy on the development of breast cancer, we compared alternative methods for combining dose-response slopes from epidemiological studies. We evaluated issues related both to summarizing data from single studies and to combining results from multiple studies. Findings related to the analysis of individual dose-response studies include: (1) a method of weighing studies that gives greater influence to dose-response slopes that conform to the linear relation of relative risk to duration can lead to large differences in calculated weights as a function of non-linearity; (2) a regression model using a variable-intercept resulted in a mean dose-response slope that increased as much as threefold when compared with the values obtained with a zero-intercept model. When combining results from multiple studies, we found: (1) calculating standard errors of mean dose-response slopes by methods that allow for both among-study and within-study variability (a random-effects type model) gave values different from a method that assumes homogeneity and equal within-study precision (a fixed-effects model); (2) the random-effects model gives mean and standard error results most similar to a bootstrap resampling method as increasing heterogeneity is observed (however, this model could give biased mean estimates compared with the bootstrap method); (3) a components-of-variance model compares favourably with the bootstrap and is easier to apply than the random-effects model. Based on these findings, we recommend the use of methods which incorporate heterogeneity to guard against underestimating the standard error. However, caution is urged because bias in point estimates can occur if extreme heterogeneity is present. Two other observations affect the interpretation of data combined from multiple studies. First, inclusion into a model of quality scores assigned by blinded reviewers had little effect on the mean dose-response slope and its standard error. Second, the number of studies required to achieve desired statistical power, varies with effect size.

Analysis of Variance↗

PubMedDate not supplied

Soluble metals in the atmosphere and their biological implications. A study to identify important aerosol components by statistical analysis of PIXE data.

Multivariate statistical analysis has been applied to time series measurements of aerosol elemental composition from PIXE analysis of filter samples, and principal components have been resolved that represent distinct particle types in an external mixture in the atmosphere. In this study, it is argued that a combination of chemical and statistical analyses of the data may be more powerful in determining chemical species in atmospheric aerosols than studied that employ mainly direct chemical analysis of chemical species in unresolved mixtures of aerosol particle samples. Sulfur is generally associated with mineral dust elements. It is reasoned that the association may represent sulfuric acid coatings on particles that can lead to mineral dissolution and solubilization of significant amounts of aluminum, iron, and other metals. Upon wet or dry deposition to the surface, the fluxes of these metals in biologically-available form may be sufficient to affect primary productivity in the world ocean and cause ecological damage in lakes. As a consequence, the fluxes of biogenic trace gases to the atmosphere may be changed, possibly leading to changes in the tropospheric concentration of ozone. The inputs to lakes of soluble aluminum, which is toxic to fish, may be partly by deposition directly from the atmosphere, thus not limited to leaching of soils by acid deposition. Human inhalation of soluble aluminum and other solubilized mineral metals may account, in part, for the observed geographic pattern of deaths attributed to chronic obstructive pulmonary disease (COPD) that show high rates in cities of the Western US and the southeast region, but low in most of the midwest and northeast.

Aerosols↗

PubMed2004

[Estimation of autonomic nervous system tension in patients with syncope of unknown origin--traps in clinical interpretation results of heart rate variability].

UNLABELLED: Voluntary character of a choice of statistical methods weakens the reliability of the results of heart rate variability assessment and based on them clinical conclusions. The aim of the study was to estimate reliability of the chosen statistical methods of analysing changes in spectral components during tilt testing (TT). MATERIAL AND METHODS: 62 patients (34 women), the average age 38.8 +/- 12.8 years, with at least 2 syncopes during the last 6 months that had not been diagnosed by other examinations, were enrolled. The control group consisted of 44 age- and sex-matched volunteers (21 women), the average age 37.4 +/- 12.6 years, who had no history of syncope. All subjects underwent tilt testing according to Westminster protocol. If the result of a passive phase was negative, 0.25 mg nitroglycerine was applied sublingually and the examination was continued for the next 20 minutes. The type of syncopal reaction was defined according to VASIS classification (the vasovagal syncope international study). The evaluation of heart rate variability was based on the frequency domain methods. The low frequency (LF), the high frequency (HF) component and the balance (the LF/HF ratio) were estimated. The response of the autonomic nervous system (AUN) to tilting was evaluated by tests comparing mean values of respective components (the quantitative analysis) and by the modulation index (deltaXFm) reflecting, in percentage terms, changes in analyzed variable values. Taking into account the obtained results there was also a qualitative analysis performed. This analysis referred to the modulation index, which reflected increase or decrease in spectral component value. RESULTS: Tilt testing explained vasovagal origin of syncope in 35 (60%) patients with syncope. Patients were divided into 3 groups according to anamnesis data and results of tilt testing. Group I consisted of 42 healthy volunteers who had negative result of TT Group II--35 patients with history of syncopes and positive result of TT, and Group III--23 patients with history of syncopes and negative result of TT. In all study groups the quantitative analysis revealed the decrease in the LF and HF component values, whereas the evaluation of autonomic nervous system reactivity based on deltaXFm showed the increase in LF power, concomitant with strongly marked, nearly uniform decrease in HF power in Group I and II. The results obtained from the qualitative analysis did not reveal statistically significant differences between study groups in distribution of defined types of autonomic nervous system reactions. CONCLUSIONS: 1. The quantitative analysis has limited credibility in clinical interpretation of changes in autonomic nervous system activity (especially in the low frequency component--LF) occurring during tilt testing. 2. The best estimation of autonomic nervous system activity during tilt testing is assured by the modulation index supplemented by the preliminary selection of data, i.e., rejection of extreme values or those rarely occurring qualitative changes in spectral components.

Adolescent↗

PubMed1997

Lack of association between bipolar disorder and tyrosine hydroxylase: a meta-analysis.

Tyrosine hydroxylase (TH) is a candidate gene extensively explored in several association studies of bipolar disorder (BD). However, because of conflicting results of independent studies and low statistical power of individual studies to detect small differences between cases and controls, reliable conclusions are difficult to formulate. A method to obtain more reliable conclusions about the involvement of the TH locus in the etiology of BD is meta-analysis. We undertook a meta-analysis of studies that investigated the association between BD and TH genetic markers. The studies were identified by means of computerized searches of several databases, and the scanning of review articles and the reference lists of the primary articles identified. More than 60 publications were reviewed, and 9 relevant articles were included in this meta-analysis, with an overall sample of 1,069 subjects (547 cases and 522 normal controls). The overall odds ratio (and confidence interval) based on combining the results of the studies was 1.02 (0.68-1.54). Test of the null hypothesis that the mean log odds ratio equals zero (chi2 = 0.11; 5 df; P > 0.05) indicated that there was no overall association between bipolar disorder and tyrosine hydroxylase.

Bipolar Disorder↗

PubMed1995

Changes in aerobic power of men, ages 25-70 yr.

This study quantified and compared the cross-sectional and longitudinal influence of age, self-report physical activity (SR-PA), and body composition (%fat) on the decline of maximal aerobic power (VO2peak). The cross-sectional sample consisted of 1,499 healthy men ages 25-70 yr. The 156 men of the longitudinal sample were from the same population and examined twice, the mean time between tests was 4.1 (+/- 1.2) yr. Peak oxygen uptake was determined by indirect calorimetry during a maximal treadmill exercise test. The zero-order correlations between VO2peak and %fat (r = -0.62) and SR-PA (r = 0.58) were significantly (P < 0.05) higher that the age correlation (r = -0.45). Linear regression defined the cross-sectional age-related decline in VO2peak at 0.46 ml.kg-1.min-1.yr-1. Multiple regression analysis (R = 0.79) showed that nearly 50% of this cross-sectional decline was due to %fat and SR-PA, adding these lifestyle variables to the multiple regression model reduced the age regression weight to -0.26 ml.kg-1.min-1.yr-1. Statistically controlling for time differences between tests, general linear models analysis showed that longitudinal changes in aerobic power were due to independent changes in %fat and SR-PA, confirming the cross-sectional results.

Adipose Tissue↗

PubMedDate not supplied

A multivariate discriminate analysis of behavioral measures in genetically nervous dogs.

For some years we have studied a strain of genetically nervous dogs in the Neuropsychiatric Research Laboratory, Veterans Administration Hospital, North Little Rock, Arkansas. In the manner of Pavlov and Gantt and later Scott and Fuller we have characterized these dogs in such descriptive terms as timid, human aversive, and catatonic-like. Behavioral tests have been administered on nearly all dogs in this longitudinal study, and we are using these data to try to develop statistical procedures to maximize the discriminatory power of the behavioral assay and to more accurately characterize the behavioral deficit. A multivariate discriminate analysis of 13 variables on 91 healthy and 63 nervous dogs assayed at 3 months of age shows: (1) that much of our present behavioral testing procedures is redundant, and (2) that simple "friendliness to humans" in the dog is as effective for discriminating between the two groups as any of the 13 measures, taken either singly or collectively.

Animals↗

PubMed1999

Crystalloids vs. colloids in fluid resuscitation: a systematic review.

OBJECTIVE: To systematically review the effects of isotonic crystalloids compared with colloids in fluid resuscitation. DATA SOURCES: Computerized bibliographic search of published research and citation review of relevant articles. STUDY SELECTION: All randomized clinical trials of adult patients requiring fluid resuscitation comparing isotonic crystalloids vs. colloids were included. Pulmonary edema, mortality, and length of stay were evaluated. Independent review of 105 articles identified 17 relevant primary studies of 814 patients. Weighted c about article inclusion was high (0.76). DATA EXTRACTION: Data on population, interventions, outcomes, and methodologic quality of the studies were obtained by duplicate independent review with differences resolved by consensus. Weighted ic on the validity assessment was moderate (0.54). DATA SYNTHESIS: No difference was observed overall between crystalloid and colloid resuscitation with respect to mortality and pulmonary edema; however, the power of the aggregated data was insufficient to detect small but potentially clinically important differences. Subgroup analysis suggested a statistically significant difference in mortality in trauma in favor of crystalloid resuscitation (relative risk 0.39, 95% confidence intervals: 0.17 to 0.89). Several methodologic issues are noteworthy regarding the primary studies, including lack of blinding (except in three studies). The type, dose, and duration of fluid administration and outcomes measured were different across these trials. CONCLUSIONS: Overall, there is no apparent difference in pulmonary edema, mortality, or length of stay between isotonic crystalloid and colloid resuscitation. Crystalloid resuscitation is associated with a lower mortality in trauma patients. Methodologic limitations preclude any evidence-based clinical recommendations. Larger well-designed randomized trials are needed to achieve sufficient power to detect potentially small differences in treatment effects if they truly exist.

Colloids↗

PubMedDate not supplied

More power to them--statistically, that is: a commentary on Studdert-Kennedy, Mody, and Brady's criticism of a critique.

The power analysis discussed above establishes that it was most unlikely that Mody et al. (1997) could make a meaningful test of the Tallal hypothesis because of inadequate n and failure to specify the effect size. Note that this is a best-case scenario, because the power analysis assumes that the analysis of variance assumptions were within reasonable boundaries (e.g., as specified by Norton's study). This was clearly not the case. In summary, the Mody et al. study fails to meet minimal scientific criteria and makes no meaningful contribution to the literature.

Analysis of Variance↗

PubMed2025

Association between NAFLD and liver cancer: A two-sample Mendelian randomization study.

Observational studies suggest an association between nonalcoholic fatty liver disease (NAFLD) and liver cancer, but its causal nature remains unclear. A 2-sample Mendelian randomization (MR) analysis was performed using NAFLD and liver cancer summary statistics from genome-wide association study databases. Instrumental variables satisfying the 3 core MR assumptions were selected. Causal effects were estimated using inverse-variance weighted, MR-Egger, weighted median, and other methods, followed by sensitivity and power analyses. All 4 MR analyses demonstrated a positive causal association between NAFLD and liver cancer risk [odds ratio > 1, inverse-variance weighted P < .001]. Sensitivity analysis indicated no significant level of multiplicity or heterogeneity in the instrumental variables, and individual single nucleotide polymorphisms had no significant impact on the results. However, statistical power was insufficient. This study provides the first MR evidence demonstrating a genetically predicted causal relationship between NAFLD and liver cancer that is consistent across subtypes. Sensitivity analyses confirmed the absence of horizontal pleiotropy or heterogeneity, strengthening the robustness of the findings. These results offer genetic support for early NAFLD intervention to reduce the risk of liver cancer. However, the limited statistical power highlights the need for larger-scale genome-wide association study to identify more and stronger genetic instruments for a more precise quantification of the causal effect of NAFLD on liver cancer risk.

Humans↗

PubMed2003

Haplotype block linkage disequilibrium mapping.

Linkage disequilibrium (LD) mapping is emerging as a powerful alternative approach to identifying genes for complex disease. However, the feasibility and success of LD mapping depend largely on the extent and pattern of LD. Erratic pattern of pair-wise LD seriously compromises LD mapping. Recently discovered haplotype block structure dramatically alleviates the irregular pattern of LD and holds the promise for mapping complex disease genes. To facilitate applications of the haplotype block LD mapping, in this report we conduct theoretical analysis for haplotype block LD mapping. We present an overall LD measure of the haplotype to quantify the LD level of the haplotype block, between the haplotype blocks, and between the haplotype block and the marker locus. Most theoretical and empirical studies of the extent of LD and evaluation of the power of LD mapping have focused on pair-wise LD and single marker LD mapping. There is a lack of systematic and integrative analysis for the haplotype block LD mapping. In this report, we develop population genetic models of the haplotype blocks and analytic tools for calculation of noncentrality parameter of the statistic for the haplotype block LD mapping. We evaluate the impact of the population parameters and disease models on the power of the haplotype block LD mapping in the hope to improve its study design. We compare the powers of the single marker LD and haplotype block LD mapping. Haplotype block structure is an important discovery. Our preliminary results of theoretic analysis further demonstrate that the haplotype block LD analysis is a breakthrough in LD mapping and is a promising tool for genome-wide association studies.

Chromosome Mapping↗

PubMed2004

On the modeling, construction, and evaluation of a probabilistic atlas of brain perfusion.

To detect subtle, abnormal perfusion patterns in brain single photon emission computer tomography (SPECT) images, it is necessary to develop quantitative methods in which computer-aided statistical analysis takes advantage of information present in databases of normal subjects. The purpose of this study was to evaluate and examine aspects of the creation and the modeling power of three statistical models for representing brain perfusion as observed in ECD-SPECT. The first model is a local model of voxel-by-voxel mean and variance. The second model is a PCA-based global model that accounts for covariance patterns in the images. The third model is an original model that is a non-linear extension to the second model. This model is based on robust statistics for modeling abnormalities. To evaluate the models, a leave-one-out procedure combined with simulations of abnormal perfusion patterns was adopted. Abnormal perfusion patterns were simulated at different locations in the brain, with different intensities and different sizes. The procedure yields receiver operator characteristics (ROC) that present a combined measure of model-fit and model-sensitivity at detecting abnormalities. The scheme can further be used to compare models as well as the influence of different preprocessing steps. In particular, the influence of different registration approaches is studied and analyzed. The results show that the original non-linear model always performed better than the other models. Finally, location-dependent detection performance was found. Most notably, a higher variation of perfusion was observed in the right frontal cortex than in the other locations studied.

Algorithms↗

PubMed2006

Meta-analysis shows association between the tryptophan hydroxylase (TPH) gene and schizophrenia.

A number of studies have suggested an association between schizophrenia and the tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH) genes. On the other hand, several studies attempting to replicate these findings have produced mixed results, possibly reflecting inadequate statistical power of the individual studies as well as the heterogeneity inherent in schizophrenia. In an attempt to clarify this inconsistency our meta-analysis has combined all the studies using multiple research methods published up to February 2006 to give a comprehensive picture of the role of three hydroxylase-related genes. The TPH A218C/A779C (OR = 1.18, 95% C.I. 1.06-1.33, P = 0.004) revealed a significant association with schizophrenia. However, the evidence for the TH and phenylalanine hydroxylase (PAH) genes was weak. No publication bias was detected in current studies. The findings, which may implicate the involvement of TPH in the pathogenesis of schizophrenia, have potentially important clinical, scientific and public health implications as well as providing a putative basis for the study of hydroxylase-related drugs. To our knowledge, this is the first meta-analysis of association between the three genes and schizophrenia.

Gene Frequency↗

PubMed1995

A cladistic analysis of phenotypic associations with haplotypes inferred from restriction endonuclease mapping or DNA sequencing. V. Analysis of case/control sampling designs: Alzheimer's disease and the apoprotein E locus.

Present-day associations between haplotypes at a candidate locus and phenotypes exist when phenotypically important mutations occurred at some point during the evolution of the current array of genetic variation. A cladistic statistical design can be defined that focuses power by using the evolutionary history of the candidate DNA region. This paper shows how cladistic methodology is used for the analysis of case/control data, a common sampling design in genetic/disease association studies. A worked example is presented of the associations for sporadic early and late-onset forms of Alzheimer's disease with the 19q13.2 chromosomal region that includes the loci for apoproteins E, CI, and CII. This analysis confirms earlier reports of a strong association of the ApoE epsilon 4 allele with Alzheimer's disease but indicates that it is premature to consider this association causal, particularly for early onset cases. Associations were also found with the epsilon 2 allele, as previously reported, and with the 1 allele at the ApoCI locus. However, this analysis indicates that it is inappropriate both statistically and medically to use single markers as risk predictors when haplotype data are available, even when the mutation leading to the marker is identified as having a strong phenotypic association.

Age of Onset↗

PubMed2006

Bayesian methods for evidence synthesis in cost-effectiveness analysis.

Recently, health systems internationally have begun to use cost-effectiveness research as formal inputs into decisions about which interventions and programmes should be funded from collective resources. This process has raised some important methodological questions for this area of research. This paper considers one set of issues related to the synthesis of effectiveness evidence for use in decision-analytic cost-effectiveness (CE) models, namely the need for the synthesis of all sources of available evidence, although these may not 'fit neatly' into a CE model. Commonly encountered problems include the absence of head-to-head trial evidence comparing all options under comparison, the presence of multiple endpoints from trials and different follow-up periods. Full evidence synthesis for CE analysis also needs to consider treatment effects between patient subpopulations and the use of nonrandomised evidence. Bayesian statistical methods represent a valuable set of analytical tools to utilise indirect evidence and can make a powerful contribution to the decision-analytic approach to CE analysis. This paper provides a worked example and a general overview of these methods with particular emphasis on their use in economic evaluation.

Bayes Theorem↗

PubMed2005

Reformulating and simplifying the DF analysis model.

DeFries-Fulker (DF) Analysis for unselected populations is reformulated as a no-intercept model with centered variables and only two independent variables. The reformulation serves three purposes. First, the original formulation implicitly estimated two different values for c2 and two values for h2. The new formulation resolves this ambiguity. Second, because the original formulation estimated h2 with the coefficient from a regression-interaction term, whether to center the interaction variables was unclear. The new formulation explicitly resolves this issue. Finally, the new formulation estimates fewer parameters, and therefore improves estimation efficiency and statistical power.

Fertility↗

PubMed1999

Bleeding complications with enoxaparin for deep venous thrombosis prophylaxis.

The safest and most efficacious method of deep venous thrombosis prophylaxis remains controversial. With the use of enoxaparin, a low-molecular-weight heparin, becoming ubiquitous in many institutions, we specifically examined bleeding complications related to its use. A case-control study was conducted on consecutive patients receiving enoxaparin prophylaxis after primary or revision total knee or total hip arthroplasty or hip hemiarthroplasty. Matched controls receiving no pharmacologic anticoagulation were identified. Patient and operative characteristics, hematologic values, and timing of enoxaparin dosing were analyzed as related to major and minor bleeding complications. A total of 152 procedures with enoxaparin and an equal number of control cases were included for a total of 304 patients. The enoxaparin group had a 23.7% total complication rate compared to 16.5% for the control group (P = .11). The power of the test was .35 and indicated that approximately 970 patients would need to be reviewed to have at least an 80% chance of finding a statistically significant difference. Major complications occurred in 5 patients (3.3%) in the enoxaparin group and 2 (1.3%) in the control group (P = .25, power = .21). Minor complications in the enoxaparin group were slightly higher but not significant at 20.4% versus 15.1% in the control group (P = .23). There were significantly fewer minor complications in the enoxaparin group after primary single-joint procedures (16.50%) than all other procedures (32.4%). Patients receiving the first dose of enoxaparin 10 hours or more postoperatively had significantly fewer complications (P = .05). The postoperative hematocrit drop was significantly greater for the enoxaparin group for all procedures (P = .003) as well as for primary single procedures (P = .0005). The postoperative transfusion requirement was significantly greater after primary single procedures (P = .02) in the enoxaparin group. One patient with an epidural catheter and receiving enoxaparin postoperatively developed an epidural hematoma. Although there were not significantly more complications with enoxaparin, there was evidence of significantly increased postoperative bleeding. The low-power analysis reveals that a large number of patients (970-1,700) are required to show a statistically significant difference in bleeding complications between the 2 groups. To minimize complications, a short period to allow initial hemiostasis postoperatively is recommended, as is preferential use of enoxaparin for primary single-joint replacements. Enoxaparin used in conjunction with an indwelling epidural catheter is not recommended.

Aged↗