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Circular analysis in systems neuroscience: the dangers of double dipping

Abstract

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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Figure 1: Intuitive diagrams for understanding circular analysis.
Figure 2: Example 1: data selection can bias pattern-information analysis.
Figure 3: Example 2: ROI definition can bias activation analysis.
Figure 4: A policy for noncircular analysis.

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Acknowledgements

We would like to thank P.A. Bandettini, R.W. Cox, J.V. Haxby, D.J. Kravitz, A. Martin, R.A. Poldrack, R.D. Raizada, Z.S. Saad, J.T. Serences and E. Vul for helpful discussions. This work was supported by the Intramural Research Program of the US National Institute of Mental Health.

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Contributions

N.K., W.K.S., P.S.F.B. and C.I.B. conceived the project and discussed all of the issues. W.K.S. contributed the data, simulation and analysis for Example 1. N.K. designed and performed all other simulations and analyses. P.S.F.B. contributed to data analysis. N.K. wrote the paper and the Supplementary Discussion and made all figures. W.K.S. and P.S.F.B. commented on drafts. C.I.B. edited the paper and guided the project.

Corresponding authors

Correspondence to Nikolaus Kriegeskorte or Chris I Baker.

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Supplementary Figures 1–4 and Supplementary Discussion (PDF 1251 kb)

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Kriegeskorte, N., Simmons, W., Bellgowan, P. et al. Circular analysis in systems neuroscience: the dangers of double dipping. Nat Neurosci 12, 535–540 (2009). https://doi.org/10.1038/nn.2303

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