Blog Archives

Correcting bias in meta-analyses: What not to do (meta-showdown Part 1)

June 1, 2017
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Correcting bias in meta-analyses: What not to do (meta-showdown Part 1)

tl;dr: Publication bias and p-hacking can dramatically inflate effect size estimates in meta-analyses. Many methods have been proposed to correct for such bias and to estimate the underlying true effect. In a large simulation study, we found out which methods do not work well under which conditions, and give recommendations what not to use. Estimated The post Correcting bias...

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Introducing the p-hacker app: Train your expert p-hacking skills

June 21, 2016
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Introducing the p-hacker app: Train your expert p-hacking skills

  Start the p-hacker app! My dear fellow scientists! “If you torture the data long enough, it will confess.” This aphorism, attributed to Ronald Coase, sometimes has been used in a disrespective manner, as if it was wrong to do creative data analysis. In fact, the art of

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Optional stopping does not bias parameter estimates (if done correctly)

April 15, 2016
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Optional stopping does not bias parameter estimates (if done correctly)

tl;dr: Optional stopping does not bias parameter estimates from a frequentist point of view if all studies are reported (i.e., no publication bias exists) and effect sizes are appropriately meta-analytically weighted. Several recent discussions on the Psychological Methods Facebook group surrounded the question whether an optional stopping procedure leads to biased effect size estimates (see

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What’s the probability that a significant p-value indicates a true effect?

November 3, 2015
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What’s the probability that a significant p-value indicates a true effect?

If the p-value is __ .05, then the probability of falsely rejecting the null hypothesis is 

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A Compendium of Clean Graphs in R

March 12, 2015
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A Compendium of Clean Graphs in R

Every data analyst knows that a good graph is worth a thousand words, and perhaps a hundred tables. But how should one create a good, clean graph? In R, this task is anything but

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What does a Bayes factor feel like?

January 29, 2015
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What does a Bayes factor feel like?

A Bayes factor (BF) is a statistical index that quantifies the evidence for a hypothesis, compared to an alternative hypothesis (for introductions to Bayes factors, see here, here or here). Although the BF is a continuous measure of evidence, humans love verbal labels, categories, and benchmarks. Labels give interpretations of the objective index – and

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Reanalyzing the Schnall/Johnson “cleanliness” data sets: New insights from Bayesian and robust approaches

June 2, 2014
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Reanalyzing the Schnall/Johnson “cleanliness” data sets: New insights from Bayesian and robust approaches

I want to present a re-analysis of the raw data from two studies that investigated whether physical cleanliness reduces the severity of moral judgments – from the original study (n = 40; Schnall, Benton, & Harvey, 2008), and from a direct replication (n = 208, Johnson, Cheung, & Donnellan, 2014). Both data sets are provided

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A comment on “We cannot afford to study effect size in the lab” from the DataColada blog

May 6, 2014
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A comment on “We cannot afford to study effect size in the lab” from the DataColada blog

In a recent post on the DataColada blog, Uri Simonsohn wrote about “We cannot afford to study effect size in the lab“. The central message is: If we want accurate effect size (ES) estimates, we need large sample sizes (he suggests four-digit n’s). As this is hardly possible in the lab we have to use

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Interactive exploration of a prior’s impact

February 21, 2014
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Interactive exploration of a prior’s impact

The probably most frequent criticism of Bayesian statistics sounds something like “It’s all subjective – with the ‘right’ prior, you can get any result you want.”. In order to approach this criticism it has been suggested to do a sensitivity analysis (or robustness analysis), that demonstrates how the choice of priors affects the conclusions drawn

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A short taxonomy of Bayes factors

January 21, 2014
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A short taxonomy of Bayes factors

I am starting to familiarize myself with Bayesian statistics. In this post I’ll show some insights I had concerning Bayes factors (BF). What are Bayes factors? Bayes factors provide a numerical value that quantifies how well a hypothesis predicts the empirical data relative to a competing hypothesis. For example, if the BF is 4, this

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