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Meta-analytic methods for fMRI, VBM and PET Software | Tutorial | Manual | Database | Web utilities | The people

Introduction

Signed Differential Mapping is a statistical technique for meta-analyzing studies on differences in brain activity or structure which used neuroimaging techniques such as fMRI, VBM or PET. SDM adopted and combined various positive features from previous methods and introduced a series of improvements and novel features. The first meta-analysis using this method has been published in the British Journal of Psychiatry .

The method

An introduction of the method can be found in the SDM Reference Manual.

Briefly, some of the features are:

• A criterion in the selection of the coordinates to avoid biases towards liberally thresholded regions
• Accounting for different sources of spatial error (e.g. coregistration mismatch or the size of the cluster), constraints to avoid a bias towards studies reporting various coordinates in close proximity, and signed maps to counteract positive and negative differences.
• Weights in the calculations: sample sizes (i.e. studies with large sample sizes contribute more) and other optional weights.
• Complementary analyses such as descriptive analysis of quartiles (which provides a "p-value-free" measure of the effect size), exploration of heterogeneity (by means of subgroup analyses and meta-regressions) and jackknife analyses (to assess the replicability of the results).

The software

Please feel free to download the software created by the SDM Project to carry out such meta-analyses.

References

Radua J and Mataix-Cols D. Voxel-wise meta-analysis of grey matter changes in obsessive-compulsive disorder. Br J Psychiatry 2009; 195:393-402.