51 research outputs found
Statistical properties of methods based on the Q-statistic for constructing a confidence interval for the between-study variance in meta-analysis
The effect sizes of studies included in a metaâanalysis do often not share a common true effect size due to differences in for instance the design of the studies. Estimates of this soâcalled betweenâstudy variance are usually imprecise. Hence, reporting a confidence interval together with a point estimate of the amount of betweenâstudy variance facilitates interpretation of the metaâanalytic results. Two methods that are recommended to be used for creating such a confidence interval are the Qâprofile and generalized Qâstatistic method that both make use of the Qâstatistic. These methods are exact if the assumptions underlying the randomâeffects model hold, but these assumptions are usually violated in practice such that confidence intervals of the methods are approximate rather than exact confidence intervals. We illustrate by means of two MonteâCarlo simulation studies with odds ratio as effect size measure that coverage probabilities of both methods can be substantially below the nominal coverage rate in situations that are representative for metaâanalyses in practice. We also show that these too low coverage probabilities are caused by violations of the assumptions of the randomâeffects model (ie, normal sampling distributions of the effect size measure and known sampling variances) and are especially prevalent if the sample sizes in the primary studies are small
Global Bifurcations in a Three-Dimensional Financial Model of "Bull and Bear" Interactions
We consider a three-dimensional nonlinear dynamic model of interacting stock and foreign exchange markets, jointly driven by the speculative activity of heterogeneous investors, and give a global dynamic analysis by using analytical and numerical tools
Small sample properties of a ridge regression estimator when there exist omitted variables
Ridge regression, Omitted variables, Mean squared error (MSE),
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