Evidence
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In low-powered studies, true effects are less likely to be detected, while any effects that are detected tend to be inflated and less likely to replicate.
Passages supplied to the Evidence version
Card 1 · Power contours: optimising sample size and precision in experimental psychology and human neuroscience
Low powered studies are less able to detect a true effect (and so make Type II errors), and are therefore more likely to report spurious effects (Type I errors) compared with high-powered studies. Furthermore, any real effects that are detected are likely to have inflated effect sizes ( Ioannidis200…
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Low powered studies are less able to detect a true effect (and so make Type II errors), and are therefore more likely to report spurious effects (Type I errors) compared with high-powered studies. Furthermore, any real effects that are detected are likely to have inflated effect sizes ( Ioannidis2008 ; Colquhoun2014 ) . These problems are common across many scientific disciplines, and estimates of power across studies in the neurosciences ( Button2013 ) yield power values in the range 8%-30%, far below the desired level of >=80%. The prevalence of low-powered studies has filled some areas of the literature with effects that fail to replicate and may well be spurious ( Ioannidis2005 ; OSC2015 ) . Most discussion of increasing statistical power has focussed on recruiting larger sample sizes, because for a given effect size, power is a function of sample size (see Figure 1 d).
Card 2 · Statistical power for cluster analysis
BACKGROUND: Cluster algorithms are gaining in popularity in biomedical research due to their compelling ability to identify discrete subgroups in data, and their increasing accessibility in mainstream software. While guidelines exist for algorithm selection and outcome evaluation, there are no firml…
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BACKGROUND: Cluster algorithms are gaining in popularity in biomedical research due to their compelling ability to identify discrete subgroups in data, and their increasing accessibility in mainstream software. While guidelines exist for algorithm selection and outcome evaluation, there are no firmly established ways of computing a priori statistical power for cluster analysis. Here, we estimated power and classification accuracy for common analysis pipelines through simulation. We systematically varied subgroup size, number, separation (effect size), and covariance structure. We then subjected generated datasets to dimensionality reduction approaches (none, multi-dimensional scaling, or uniform manifold approximation and projection) and cluster algorithms (k-means, agglomerative hierarchical clustering with Ward or average linkage and Euclidean or cosine distance, HDBSCAN). Finally, we directly compared the statistical power of discrete (k-means), "fuzzy" (c-means), and finite mixture …
Card 3 · Sample size calculations for the experimental comparison of multiple algorithms on multiple problem instances
Abstract This work presents a statistically principled method for estimating the required number of instances in the experimental comparison of multiple algorithms on a given problem class of interest. This approach generalises earlier results by allowing researchers to design experiments based on t…
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Abstract This work presents a statistically principled method for estimating the required number of instances in the experimental comparison of multiple algorithms on a given problem class of interest. This approach generalises earlier results by allowing researchers to design experiments based on the desired best, worst, mean or median-case statistical power to detect differences between algorithms larger than a certain threshold. Holm’s step-down procedure is used to maintain the overall significance level controlled at desired levels, without resulting in overly conservative experiments. This paper also presents an approach for sampling each algorithm on each instance, based on optimal sample size ratios that minimise the total required number of runs subject to a desired accuracy in the estimation of paired differences. A case study investigating the effect of 21 variants of a custom-tailored Simulated Annealing for a class of scheduling problems is used to illustrate the applicati …
Card 4 · Detecting the skewness of data from the sample size and the five-number summary
For clinical studies with continuous outcomes, when the data are potentially skewed, researchers may choose to report the whole or part of the five-number summary (the sample median, the first and third quartiles, and the minimum and maximum values), rather than the sample mean and standard deviatio…
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For clinical studies with continuous outcomes, when the data are potentially skewed, researchers may choose to report the whole or part of the five-number summary (the sample median, the first and third quartiles, and the minimum and maximum values), rather than the sample mean and standard deviation. For the studies with skewed data, if we include them in the classical meta-analysis for normal data, it may yield misleading or even wrong conclusions. In this paper, we develop a flow chart and three new tests for detecting the skewness of data from the sample size and the five-number summary. Simulation studies demonstrate that our new tests are able to control the type I error rates, and meanwhile provide good statistical power. A real data example is also analyzed to demonstrate the usefulness of the skewness tests in meta-analysis and evidence-based practice.
Card 5 · Power contours: optimising sample size and precision in experimental psychology and human neuroscience
Low powered studies are less able to detect a true effect (and so make Type II errors), and are therefore more likely to report spurious effects (Type I errors) compared with high-powered studies. Furthermore, any real effects that are detected are likely to have inflated effect sizes ( Ioannidis200…
Read full passage excerpt
Low powered studies are less able to detect a true effect (and so make Type II errors), and are therefore more likely to report spurious effects (Type I errors) compared with high-powered studies. Furthermore, any real effects that are detected are likely to have inflated effect sizes ( Ioannidis2008 ; Colquhoun2014 ) . These problems are common across many scientific disciplines, and estimates of power across studies in the neurosciences ( Button2013 ) yield power values in the range 8%-30%, far below the desired level of >=80%. The prevalence of low-powered studies has filled some areas of the literature with effects that fail to replicate and may well be spurious ( Ioannidis2005 ; OSC2015 ) . Most discussion of increasing statistical power has focussed on recruiting larger sample sizes, because for a given effect size, power is a function of sample size (see Figure 1 d).
Model-reported card use
Card 1 · fact
Affected output: true effects are less likely to be detected, while any effects that are detected tend to be inflated and less likely to replicate
Model explanation: Supplied the concrete consequences of low power used in the new paragraph, replacing a generic statement about power being important.
Card 5 · expression
Affected output: In low-powered studies, true effects are less likely to be detected, while any effects that are detected tend to be inflated
Model explanation: Provided the contrastive observation-then-consequence sentence shape used to open the paragraph.