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Two-level spatially structured models in spatio-temporal disease mapping
The objective is to present a family of flexible models to analyze real data naturally organized in two different levels of spatial aggregation like municipalities within health areas or provinces, or counties within states. Model fitting and inference will be carried out using integrated nested Laplace approximations. The performance of the new models compared to models including a single spatial random effect is assessed by simulation. Results show good behavior of the proposed two-level spatially structured models in terms of several criteria. Brain cancer mortality data in the municipalities of two regions in Spain wil...
Source: Statistical Methods in Medical Research - August 25, 2016 Category: Statistics Authors: Ugarte, M. D., Adin, A., Goicoa, T. Tags: Special Issue Articles Source Type: research

Editorial
(Source: Statistical Methods in Medical Research)
Source: Statistical Methods in Medical Research - August 25, 2016 Category: Statistics Authors: Lawson, A. B., Lee, D., MacNab, Y. Tags: Editorial Source Type: research

Estimating the sample size for a pilot randomised trial to minimise the overall trial sample size for the external pilot and main trial for a continuous outcome variable
Sample size justification is an important consideration when planning a clinical trial, not only for the main trial but also for any preliminary pilot trial. When the outcome is a continuous variable, the sample size calculation requires an accurate estimate of the standard deviation of the outcome measure. A pilot trial can be used to get an estimate of the standard deviation, which could then be used to anticipate what may be observed in the main trial. However, an important consideration is that pilot trials often estimate the standard deviation parameter imprecisely. This paper looks at how we can choose an external pi...
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Whitehead, A. L., Julious, S. A., Cooper, C. L., Campbell, M. J. Tags: Articles Source Type: research

How big should the pilot study for my cluster randomised trial be?
There is currently a lot of interest in pilot studies conducted in preparation for randomised controlled trials. This paper focuses on sample size requirements for external pilot studies for cluster randomised trials. We consider how large an external pilot study needs to be to assess key parameters for input to the main trial sample size calculation when the primary outcome is continuous, and to estimate rates, for example recruitment rates, with reasonable precision. We used simulation to provide the distribution of the expected number of clusters for the main trial under different assumptions about the natural cluster s...
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Eldridge, S. M., Costelloe, C. E., Kahan, B. C., Lancaster, G. A., Kerry, S. M. Tags: Articles Source Type: research

Decision-theoretic designs for small trials and pilot studies: A review
Pilot studies and other small clinical trials are often conducted but serve a variety of purposes and there is little consensus on their design. One paradigm that has been suggested for the design of such studies is Bayesian decision theory. In this article, we review the literature with the aim of summarizing current methodological developments in this area. We find that decision-theoretic methods have been applied to the design of small clinical trials in a number of areas. We divide our discussion of published methods into those for trials conducted in a single stage, those for multi-stage trials in which decisions are ...
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Hee, S. W., Hamborg, T., Day, S., Madan, J., Miller, F., Posch, M., Zohar, S., Stallard, N. Tags: Articles Source Type: research

A review of statistical designs for improving the efficiency of phase II studies in oncology
Phase II oncology trials are carried out to assess whether an experimental anti-cancer treatment shows sufficient signs of effectiveness to justify being tested in a phase III trial. Traditionally such trials are conducted as single-arm studies using a binary response rate as the primary endpoint. In this article, we review and contrast alternative approaches for such studies. Each approach uses only data that are necessary for the traditional analysis. We consider two broad classes of methods: ones that aim to improve the efficiency using novel design ideas, such as multi-stage and multi-arm multi-stage designs; and ones ...
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Wason, J. M., Jaki, T. Tags: Articles Source Type: research

Statistical challenges in assessing potential efficacy of complex interventions in pilot or feasibility studies
Early phase trials of complex interventions currently focus on assessing the feasibility of a large randomised control trial and on conducting pilot work. Assessing the efficacy of the proposed intervention is generally discouraged, due to concerns of underpowered hypothesis testing. In contrast, early assessment of efficacy is common for drug therapies, where phase II trials are often used as a screening mechanism to identify promising treatments. In this paper, we outline the challenges encountered in extending ideas developed in the phase II drug trial literature to the complex intervention setting. The prevalence of mu...
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Wilson, D. T., Walwyn, R. E., Brown, J., Farrin, A. J., Brown, S. R. Tags: Articles Source Type: research

Pilot Studies in clinical research
(Source: Statistical Methods in Medical Research)
Source: Statistical Methods in Medical Research - May 18, 2016 Category: Statistics Authors: Julious, S. A. Tags: Editorial Source Type: research

Comment on 'A vine copula mixed effect model for trivariate meta-analysis of diagnostic test accuracy studies accounting for disease prevalence
(Source: Statistical Methods in Medical Research)
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Nikoloulopoulos, A. K. Tags: Response from the Author Source Type: research

Comment on 'A vine copula mixed effect model for trivariate meta-analysis of diagnostic test accuracy studies accounting for disease prevalence by Aristidis K Nikoloulopoulos
(Source: Statistical Methods in Medical Research)
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Hoyer, A., Kuss, O. Tags: Letter to the Editor Source Type: research

Book review
(Source: Statistical Methods in Medical Research)
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Emmert-Streib, F. Tags: Book review Source Type: research

A graphical method to assess distribution assumption in group-based trajectory models
Group-based trajectory models had a rapid development in the analysis of longitudinal data in clinical research. In these models, the assumption of homoscedasticity of the residuals is frequently made but this assumption is not always met. We developed here an easy-to-perform graphical method to assess the assumption of homoscedasticity of the residuals to apply especially in group-based trajectory models. The method is based on drawing an envelope to visualize the local dispersion of the residuals around each typical trajectory. Its efficiency is demonstrated using data on CD4 lymphocyte counts in patients with human immu...
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Elsensohn, M.-H., Klich, A., Ecochard, R., Bastard, M., Genolini, C., Etard, J.-F., Gustin, M.-P. Tags: Articles Source Type: research

Testing for association in case-control genome-wide association studies with shared controls
The statistical analysis of genome-wide association studies (GWASs) with multiple diseases and shared controls (SCs) is discussed. The usual method for analyzing data from these studies is to compare each individual disease with either the SCs or the pooled controls which include other diseases. We observed that applying individual association tests can be problematic because these tests may suffer from power loss in detecting significant associations between diseases and single-nucleotide polymorphism or copy number variant. We propose here a two-stage procedure wherein we first apply an overall chi-square test for multip...
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Chen, Z., Huang, H., Ng, H. K. T. Tags: Articles Source Type: research

Interval estimation of random effects in proportional hazards models with frailties
Semi-parametric frailty models are widely used to analyze clustered survival data. In this article, we propose the use of the hierarchical likelihood interval for individual frailties. We study the relationship between hierarchical likelihood, empirical Bayesian, and fully Bayesian intervals for frailties. We show that our proposed interval can be interpreted as a frequentist confidence interval and Bayesian credible interval under a uniform prior. We also propose an adjustment of the proposed interval to avoid null intervals. Simulation studies show that the proposed interval preserves the nominal confidence level. The pr...
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Ha, I. D., Vaida, F., Lee, Y. Tags: Articles Source Type: research

Estimating the prevalence of transmitted HIV drug resistance using pooled samples
We present a Bayesian model for pooled-testing data that garners more information from each resistance assay conducted, compared with individual testing. We expand on previous pooling methods to account for uncertainty about the population distribution of within-subject resistance levels. In addition, our model accounts for measurement error of the resistance assay, and this added uncertainty naturally propagates through the Bayesian model to our inference on the prevalence parameter. We conduct a simulation study that informs our pool size recommendations and that shows that this model renders the prevalence parameter ide...
Source: Statistical Methods in Medical Research - April 21, 2016 Category: Statistics Authors: Finucane, M. M., Rowley, C. F., Paciorek, C. J., Essex, M., Pagano, M. Tags: Articles Source Type: research