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Author: Gary G Koch (69)


Dec
1969

Multiplicity issues can be multidimensional: A confirmatory clinical trial may be designed to have efficacy assessed with two or more primary endpoints, for multiple dose groups, and at several post-baseline visits. Controlling for multiplicity in this situation is challenging because there can be a hierarchy with respect to some but not all measurements. If the higher dose is considered more efficacious, multiplicity approach may evaluate the higher dose with higher priority through a fixed sequential testing framework for dose assessments in combination with a Hochberg approach for endpoints.

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Sep
2017

Cardiovascular (CV) reactivity to psychological stress has been implicated in the development and exacerbation of cardiovascular disease (CVD). Although high CV reactivity traditionally is thought to convey greater risk of CVD, the relationship between reactivity and clinical outcomes is inconsistent and may depend on the patient population under investigation. The present study examined CV reactivity in patients with heart failure (HF) and its potential association with long-term clinical outcomes.

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Dec
2017

Conditional power based on summary statistic by comparing outcomes (such as the sample mean) directly between 2 groups is a convenient tool for decision making in randomized controlled trial studies. In this paper, we extend the traditional summary statistic-based conditional power with a general model-based assessment strategy, where the test statistic is based on a regression model. Asymptotic relationships between parameter estimates based on the observed interim data and final unobserved data are established, from which we develop an analytic model-based conditional power assessment for both Gaussian and non-Gaussian data.

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Dec
1969

Dichotomous endpoints in clinical trials have only two possible outcomes, either directly or via categorization of an ordinal or continuous observation. It is common to have missing data for one or more visits during a multi-visit study. This paper presents a closed form method for sensitivity analysis of a randomized multi-visit clinical trial that possibly has missing not at random (MNAR) dichotomous data.

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Dec
1969

Clinical trials are designed to compare treatment effects when applied to samples from the same population. Randomization is used so that the samples are not biased with respect to baseline covariates that may influence the efficacy of the treatment. We develop randomization-based covariance adjustment methodology to estimate the log hazard ratios and their confidence intervals of multiple treatments in a randomized clinical trial with time-to-event outcomes and missingness among the baseline covariates.

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Dec
1969

Multiplicity is an important statistical issue that arises in clinical trials when the efficacy of the test treatment is evaluated in multiple ways. The major concern for multiplicity is that uncontrolled multiple assessments lead to inflated family-wise Type I error, and they thereby undermine the integrity of the statistical inferences. Multiplicity comes from different sources, for example, making inferences either on the overall population or some pre-specified sub-populations, while multiple endpoints need to be evaluated for each population.

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Jan
2017

Heart failure (HF) is a chronic disease that compromises patients' quality of life (QoL). Interventions designed to reduce distress and improve disease self-management are needed. We evaluated the efficacy of a telephone-based coping skills training (CST) intervention.

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Sep
2016

Propensity score (PS) methods have been used extensively to adjust for confounding factors in the statistical analysis of observational data in comparative effectiveness research. There are four major PS-based adjustment approaches: PS matching, PS stratification, covariate adjustment by PS, and PS-based inverse probability weighting. Though covariate adjustment by PS is one of the most frequently used PS-based methods in clinical research, the conventional variance estimation of the treatment effects estimate under covariate adjustment by PS is biased.

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Mar
2016

Anthracyclines are a class of antitumor compounds that are successful and widely used but suffer from cardiotoxicity and acquired tumor resistance. Formaldehyde interacts with anthracyclines to enhance antitumor efficacy, bypass resistance mechanisms, improve the therapeutic profile, and change the mechanism of action from a topoisomerase II poison to a DNA cross-linker. Contrary to current dogma, we show that both efficient DNA cross-linking and potent synergy in combination with formaldehyde correlate with the anthracycline's ability to form cyclic formaldehyde conjugates as oxazolidine moieties and that the cyclic conjugates are better cross-linking agents and cytotoxins than acyclic conjugates.

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Dec
1969

Insulin-resistant subjects develop more severe and diffuse coronary artery atherosclerosis than insulin-sensitive controls but the mechanisms that mediate this atherosclerosis phenotype are unknown.
To determine the metabolic parameters that associate with the severity of coronary atherosclerosis in insulin resistant pigs fed a high fat/high NaCl diet.
The primary endpoint was severity of coronary atherosclerosis in adult pigs (Sus scrofa, n = 37) fed a high fat diet that also contained high NaCl (56% above recommended levels) for 1 year.

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Dec
1969

Time-to-event or dichotomous outcomes in randomized clinical trials often have analyses using the Cox proportional hazards model or conditional logistic regression, respectively, to obtain covariate-adjusted log hazard (or odds) ratios. Nonparametric Randomization-Based Analysis of Covariance (NPANCOVA) can be applied to unadjusted log hazard (or odds) ratios estimated from a model containing treatment as the only explanatory variable. These adjusted estimates are stratified population-averaged treatment effects and only require a valid randomization to the two treatment groups and avoid key modeling assumptions (e.

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Jul
2015

The past decade has seen substantial progress in understanding the pathobiology, natural history, and clinical significance of idiopathic pulmonary fibrosis (IPF), culminating in the establishment of two effective medical therapies. Now seems an important time to reconsider the design and conduct of future IPF clinical trials. Building on lessons learned over the past decade, we use this perspective to lay out four key considerations for moving forward effectively and efficiently with the next generation of clinical trials in IPF.

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May
2015

Preclinical evaluation of candidate human immunodeficiency virus (HIV) vaccines entails challenge studies whereby non-human primates such as macaques are vaccinated with either an active or control vaccine and then challenged (exposed) with a simian-version of HIV. Repeated low-dose challenge (RLC) studies in which each macaque is challenged multiple times (either until infection or some maximum number of challenges is reached) are becoming more common in an effort to mimic natural exposure to HIV in humans. Statistical methods typically employed for the testing for a vaccine effect in RLC studies include a modified version of Fisher's exact test as well as large sample approaches such as the usual log-rank test.

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May
2015

Repeated measurement designs have been widely used in various randomized controlled trials for evaluating long-term intervention efficacies. For some clinical trials, the primary research question is how to compare two treatments at a fixed time, using a t-test. Although simple, robust, and convenient, this type of analysis fails to utilize a large amount of collected information.

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Dec
1969

Covariate-adjusted sensitivity analyses is proposed for missing time-to-event outcomes. The method invokes multiple imputation (MI) for the missing failure times under a variety of specifications regarding the post-withdrawal tendency for having the event of interest. With a clinical trial example, we compared methods of covariance analyses for time-to-event data, i.

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Dec
2014

The cohort design allows investigators to explore the genetic basis of a variety of diseases and traits in a single study while avoiding major weaknesses of the case-control design. Most cohort studies employ multistage cluster sampling with unequal probabilities to conveniently select participants with desired characteristics, and participants from different clusters might be genetically related. Analysis that ignores the complex sampling design can yield biased estimation of the genetic association and inflation of the type I error.

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Dec
1969

Substantial heterogeneity in treatment effects across subgroups can cause significant findings in the overall population to be driven predominantly by those of a certain subgroup, thus raising concern on whether the treatment should be prescribed for the least benefitted subgroup. Because of its low power, a nonsignificant interaction test can lead to incorrectly prescribing treatment for the overall population. This article investigates the power of the interaction test and its implications.

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Jun
2014

Adherence of pathogens to cellular targets is required to initiate most infections. Defining strategies that interfere with adhesion is therefore important for the development of preventative measures against infectious diseases. As an adhesin to host extracellular matrix proteins and human keratinocytes, the trimeric autotransporter adhesin DsrA, a proven virulence factor of the Gram-negative bacterium Haemophilus ducreyi, is a potential target for vaccine development.

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Dec
1969

This article presents a multiple imputation method for sensitivity analyses of time-to-event data with possibly informative censoring. The imputed time for censored values is drawn from the failure time distribution conditional on the time of follow-up discontinuation. A variety of specifications regarding the post-discontinuation tendency of having events can be incorporated in the imputation through a hazard ratio parameter for discontinuation versus continuation of follow-up.

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Dec
1969

The effects of treatments within demographic and clinical subgroups of patients are of major interest in most confirmatory clinical trials. Potential factors for defining subgroups include gender, age, disease severity, and geographic region. A major statistical issue for the interpretation of treatment comparisons for subgroups is whether the role of a subgroup is inferential, supportive, or exploratory through respectively corresponding to a primary, key secondary, or hypothesis-generating assessment.

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Mar
2014

Neurobehavioral functioning is widely recognized as being an important consideration in lung transplant candidates, but little is known about whether these factors are related to clinical outcomes. The present study examined the relationship of neurobehavioral functioning, including measures of executive function and memory, depression, and anxiety, to long-term survival among lung transplant recipients.
The sample was drawn from 201 patients who underwent transplantation at Duke University and Washington University who participated in a dual-site clinical trial investigating medical and psychosocial outcomes in transplant candidates with end-stage lung disease.

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Dec
1969

In recent years, there has been increasing interest in compounds that have potential to slow down the structural joint damage in rheumatoid arthritis (RA) patients. Radiographs are instrumental in assessing structure damage in RA. Radiographic analyses results have become essential in establishing a "delay in structural progression" claim in newly developed agents for the treatment of RA.

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Jul
2013

Lorcaserin is a selective 5-HT2C agonist evaluated for weight management in clinical trials. Echocardiographic monitoring was conducted to test the hypothesis that selective 5-HT2C agonism would avoid valvular heart disease.
Echocardiographic and weight change data from 5249 obese and overweight patients in 3 phase 3 trials were integrated.

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Mar
2013

Depression has been related to mortality in coronary heart disease (CHD) patients, but few studies have evaluated the role of anxiety or the role of the co-occurrence of depression and anxiety. We examined whether anxiety is associated with increased risk of mortality after accounting for depression in individuals with established CHD.
The cohort was composed of 934 men and women with confirmed CHD (mean age, 62±11 years) who completed the Hospital Anxiety and Depression scale (HADS) during hospitalization for coronary angiography.

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Mar
2013

In the context of randomized clinical trials with time-to-event outcomes, estimates of covariate-adjusted log hazard ratios for comparing two treatments are obtained via nonparametric analysis of covariance by forcing the difference in means for covariables to zero. The method avoids the assumption of proportional hazards for each of the covariates, and it provides an adjusted analysis for the same population average treatment effect that the unadjusted analysis addresses. It is primarily useful in regulatory clinical trials that require analyses to be specified a priori.

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Mar
2013

This paper describes how a multistage analysis strategy for a clinical trial can assess a sequence of hypotheses that pertain to successively more stringent criteria for excess risk exclusion or superiority for a primary endpoint with a low event rate. The criteria for assessment can correspond to excess risk of an adverse event or to a guideline for sufficient efficacy as in the case of vaccine trials. The proposed strategy is implemented through a set of interim analyses, and success for one or more of the less stringent criteria at an interim analysis can be the basis for a regulatory submission, whereas the clinical trial continues to accumulate information to address the more stringent, but not futile, criteria.

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Nov
2012

To assess concomitant simultaneous effects on multiple end points using global statistical methods in phase II acute heart failure studies.
Using simulations we have assessed different statistical methods to evaluate concomitant effects of a new intervention on dyspnea relief (using 2 measures), length of hospital stay, worsening heart failure to 5 days, mortality, and heart failure readmission to 30 days. Treatment effect scenarios included large (20% to 28% relative improvements) and very large (30% to 43% relative improvements) effects among others.

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Dec
1969

It is not uncommon to have experimental drugs under different stages of development for a given disease area. Methods are proposed for use when another treatment arm is to be added mid-study to an ongoing clinical trial. Monte Carlo simulation was used to compare potential analytical approaches for pairwise comparisons through a difference in means in independent normal populations including (1) a linear model adjusting for the design change (stage effect), (2) pooling data across the stages, or (3) the use of an adaptive combination test.

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May
2011

A recent three-arm parallel groups randomized clinical prevention trial had a protocol deviation causing participants to have fewer active doses of an in-office treatment than planned. The original statistical analysis plan stipulated a minimal assumption randomization-based extended Mantel-Haenszel (EMH) trend test of the high frequency, low frequency, and zero frequency treatment groups and a binary outcome. Thus a dose-weighted adjusted EMH (DWAEMH) test was developed with an extra set of weights corresponding to the number of active doses actually available, in the spirit of a pattern mixture model.

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Sep
2011

Clinically relevant endpoints cannot be routinely targeted with reasonable power in a small study. Hence, proof-of-concept studies are often powered to a primary surrogate endpoint. However, in acute heart failure (AHF) effects on surrogates have not translated into clinical benefit in confirmatory studies.

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Mar
2011

Coping Effectively with Heart Failure (COPE-HF) is an ongoing randomized clinical trial funded by the National Institutes of Health to evaluate if a coping skills training (CST) intervention will result in improved health status and quality of life as well as reduced mortality and hospitalizations compared with a heart failure education (HFE) intervention.
Two hundred heart failure (HF) patients recruited from the Duke University Medical Center and the University of North Carolina Hospital system will be randomized to a CST intervention (16 weekly 30-minute telephone counseling sessions including motivational interviewing and individually tailored cognitive behavioral therapy) or to an HFE intervention (16 weekly 30-minute telephone sessions including education and symptom monitoring). Primary outcomes will include postintervention effects on HF biomarkers (B-type natriuretic peptide, ejection fraction) and quality of life, as well as long-term clinical outcomes (hospitalizations and death).

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Jan
2011

The purpose of this study was to assess the impact of changes in symptoms of depression over a 1-year period on subsequent clinical outcomes in heart failure (HF) patients.
Emerging evidence shows that clinical depression, which is prevalent among patients with HF, is associated with a poor prognosis. However, it is uncertain how changes in depression symptoms over time may relate to clinical outcomes.

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Sep
2010

The purpose of this explanatory analysis was to investigate the relationship between ST-segment depression and the rate-pressure product (RPP) during exercise to determine whether ranolazine's mechanism of action was related to a reduction in myocardial oxygen demand or preservation of myocardial oxygen supply.
In patients with stable ischemic heart disease, ranolazine increases exercise duration and reduces maximal ST-segment depression while exerting minimal effects on heart rate and blood pressure, although its mechanism of action during exercise has not been investigated.
Patients with stable ischemic heart disease (n = 191) were randomly allocated to a 4-period, double-blind, balanced Latin square crossover study to receive placebo, and ranolazine 500, 1,000, and 1,500 mg twice daily (bid) for 1 week each.

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Jul
2010

This paper discusses the application of multivariate Mann-Whitney estimators to the comparison of two treatments for a strictly ordinal response variable in a crossover study with four sequence groups and three periods. Ways of managing randomly missing data and nonparametric covariance adjustment for no differences among groups for a baseline period have consideration as well. Estimators pertaining to treatment comparisons in linear logistic models for the Mann-Whitney estimators have determination through a Bradley-Terry model for dimension reduction and weighted least squares.

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May
2010

The cost for conducting a "thorough QT/QTc study" is substantial and an unsuccessful outcome of the study can be detrimental to the safety profile of the drug, so sample size calculations play a very important role in ensuring adequate power for a thorough QT study. Current literature offers some help in designing such studies, but these methods have limitations and mostly apply only in the context of linear mixed models with compound symmetry covariance structure. It is not evident that such models can satisfactorily be employed to represent all kinds of QTc data, and the existing literature inadequately addresses whether there is a change in sample size and power for more general covariance structures for the linear mixed models.

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May
2010

For time-to-event data, the power of the two sample logrank test for the comparison of two treatment groups can be greatly influenced by the ratio of the number of patients in each of the treatment groups. Despite the possible loss of power, unequal allocations may be of interest due to a need to collect more data on one of the groups or to considerations related to the acceptability of the treatments to patients. Investigators pursuing such designs may be interested in the cost of the unbalanced design relative to a balanced design with respect to the total number of patients required for the study.

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Nov
2009

Elevated procoagulant levels have been correlated with increased thrombin generation in vitro and with increased venous thromboembolism (VTE) risk in epidemiological studies. Thrombin generation tests are increasingly being employed as a high throughput method to provide a global measure of procoagulant activity in plasma samples. The objective of this study was to distinguish the effects of assay conditions [tissue factor (TF), thrombomodulin, platelets/lipids] and factor levels on thrombin generation parameters, and determine the conditions and parameters with the highest sensitivity and specificity for detecting elevated factor levels.

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Jan
2010

We consider regulatory clinical trials that require a prespecified method for the comparison of two treatments for chronic diseases (e.g. Chronic Obstructive Pulmonary Disease) in which patients suffer deterioration in a longitudinal process until death occurs.

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Dec
2009

Heparin cofactor II (HCII) is a serine protease inhibitor (serpin) that has been shown to be a predictor of decreased atherosclerosis in the elderly and protective against atherosclerosis in mice. HCII inhibits thrombin in vitro and HCII-thrombin complexes have been detected in human plasma. Moreover, the mechanism of protection against atherosclerosis in mice was determined to be the inhibition of thrombin.

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Dec
2009

Doxazolidine (Doxaz) is a functionally distinct formaldehyde conjugate of doxorubicin (Dox) that induces cancer cell death in Dox-sensitive and resistant cells. Pentyl PABC-Doxaz (PPD) is a prodrug of Doxaz that is activated by carboxylesterase 2 (CES2), which is expressed by liver, non-small-cell lung, colon, pancreatic, renal, and thyroid cancer cells. Here, we demonstrate that in two murine models, PPD was effective at slowing tumor growth and demonstrated markedly reduced cardiotoxic and nephrotoxic effects, as well as better tolerance, relative to Dox.

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Sep
2009

This article describes applications of extensions of bivariate rank sum statistics to the crossover design with four sequence groups for two treatments. A randomized clinical trial in ophthalmology provides motivating background for the discussion. The bilateral design for this study has four sequence groups T:T, T:P, P:T, and P:P, respectively, for T as test treatment or P as placebo in the corresponding order for the left and right eyes.

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Sep
2009

The purpose of our study was to determine the ability of electrocardiographic (ECG) criteria derived from prior angiographic-ECG correlative studies to identify life-threatening coronary artery obstructive lesions.
We studied 128 consecutive patients referred from the emergency department for emergent coronary angiography for symptoms and ECG changes suggesting an acute coronary event. Using ECG criteria derived from prior studies, we attempted to predict not only the vessel housing the culprit lesion, but whether the lesion was located proximally in that vessel, and then determined the positive and negative predictive values (PPV and NPV) of the criteria used.

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Sep
2008

To identify potential factors associated with failed retrieval of the Günther Tulip inferior vena cava (IVC) filter.
A retrospective review was performed of patients who underwent placement of the Günther Tulip filter with at least one attempt at filter retrieval over a 3-year period. Patient demographics, filter dwell time, filter angulation, and filter leg protrusion were analyzed.

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Dec
1969

According to the regulatory requirements for multiple-dose factorial designs, a combination drug must have confirmatory evidence for being more effective than each component drug alone. An incomplete factorial design may be employed to evaluate some combination drugs because of resource constraints and priorities. In this paper, we compare the powers for four different patterns of sample size allocations in two incomplete factorial designs, with two combination drug doses and fixed total sample size.

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Feb
2008

To estimate relative efficiencies of the 7 rheumatoid arthritis (RA) Core Data Set measures to distinguish adalimumab from control treatments in 4 clinical trials.
Four adalimumab clinical trials were analyzed for arithmetic and percentage changes for each Core Data Set measure from baseline to endpoint: 3 assessor/physician measures -- swollen joints, tender joints, and global estimate; 1 laboratory test -- C-reactive protein; and 3 patient measures -- physical function, pain, and global estimate. Relative efficiencies of each measure to distinguish adalimumab from control group responses were assessed, with tender joint count as the referent measure.

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Jul
2007

The goal of public health research often involves estimating clinical outcomes for a broad target population. The gold standard for the basis of such inference is a nationally representative survey that includes a clinical component. The cost of this gold standard can be prohibitive, and alternative approaches are needed.

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Feb
2008

Assessment of non-inferiority is often performed using a one-sided statistical test through an analogous one-sided confidence limit. When the focus of attention is the difference in success rates between test and active control proportions, the lower confidence limit is computed, and many methods exist in the literature to address this objective. This paper considers methods which have been shown to be popular in the literature and have surfaced in this research as having good performance with respect to controlling type I error at the specified level.

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Feb
2007

Depression is widely recognized as a risk factor in patients with coronary heart disease. However, patients with heart failure (HF) have been less frequently studied, and the effect of depression on prognosis, independent of disease severity, is uncertain.
Two hundred four outpatients having a diagnosis of HF, with a ventricular ejection fraction of 40% or less, underwent baseline assessments including evaluation of depressive symptoms using the Beck Depression Inventory and of HF severity determined by plasma N-terminal pro-B-type natriuretic peptide.

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