Review
False positive rates in Voxel-based Morphometry studies of the human brain: Should we be worried?

https://doi.org/10.1016/j.neubiorev.2015.02.008Get rights and content
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open access

Highlights

  • Methodological factors influencing the results of a VBM study are reviewed.

  • VBM with balanced designs is not vulnerable to high false positive rate.

  • Sample size, smoothing and modulation do not influence false positive rate.

  • False positives are mainly located in the neocortex, in particular the frontal lobe.

  • These results were replicated in two independent datasets.

Abstract

Voxel-based Morphometry (VBM) is a widely used automated technique for the analysis of neuroanatomical images. Despite its popularity within the neuroimaging community, there are outstanding concerns about its potential susceptibility to false positive findings. Here we review the main methodological factors that are known to influence the results of VBM studies comparing two groups of subjects. We then use two large, open-access data sets to empirically estimate false positive rates and how these depend on sample size, degree of smoothing and modulation. Our review and investigation provide three main results: (i) when groups of equal size are compared false positive rate is not higher than expected, i.e. about 5%; (ii) the sample size, degree of smoothing and modulation do not appear to influence false positive rate; (iii) when they exist, false positive findings are randomly distributed across the brain. These results provide reassurance that VBM studies comparing groups are not vulnerable to the higher than expected false positive rates that are evident in single case VBM.

Keywords

Neuroimaging
Voxel-based Morphometry
False positive rate
Unbalanced design
Balanced design

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1

These authors contributed to this work equally.