postcards from nowhere
...or triple entendre, or even more [depending on your source].
Stolen from Neuroanthropology's Wednesday Round Up #62:
Research Digest, It’s Those Voodoo Correlations Again … Brain Imagers Accused of “Double Dipping”Others have already written about the new voodoo-esque paper by Kriegeskorte et al. (2009). Having blogged extensively about the original controversy, I don't have anything to add... other than the links above... and some fun and wholesome pictures.
More methods problems for imaging researchers – using the same data twice, first to find the area and then to show that area is really the one responsible for whatever hypothesis is at stake. For more commentary, see Neuroskeptic, Mind Hacks, and Newsweek.
Kriegeskorte N, Simmons WK, Bellgowan PS, Baker CI. (2009). Circular analysis in systems neuroscience: the dangers of double dipping. Nat Neurosci. 12:535-40.
A neuroscientific experiment typically generates a large amount of data, of which only a small fraction is analyzed in detail and presented in a publication. However, selection among noisy measurements can render circular an otherwise appropriate analysis and invalidate results. Here we argue that systems neuroscience needs to adjust some widespread practices to avoid the circularity that can arise from selection. In particular, 'double dipping', the use of the same dataset for selection and selective analysis, will give distorted descriptive statistics and invalid statistical inference whenever the results statistics are not inherently independent of the selection criteria under the null hypothesis. To demonstrate the problem, we apply widely used analyses to noise data known to not contain the experimental effects in question. Spurious effects can appear in the context of both univariate activation analysis and multivariate pattern-information analysis. We suggest a policy for avoiding circularity.
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