title: Global, voxel, and cluster tests, by theory and permutation, for a difference between two groups of structural MR images of the brain.
abstract: We describe almost entirely automated procedures for estimation of global, voxel, and cluster-level statistics to test the null hypothesis of zero neuroanatomical difference between two groups of structural magnetic resonance imaging (MRI) data. Theoretical distributions under the null hypothesis are available for 1) global tissue class volumes; 2) standardized linear model [analysis of variance (ANOVA and ANCOVA)] coefficients estimated at each voxel; and 3) an area of spatially connected clusters generated by applying an arbitrary threshold to a two-dimensional (2-D) map of normal statistics at voxel level. We describe novel methods for economically ascertaining probability distributions under the null hypothesis, with fewer assumptions, by permutation of the observed data. Nominal Type I error control by permutation testing is generally excellent; whereas theoretical distributions may be over conservative. Permutation has the additional advantage that it can be used to test any statistic of interest, such as the sum of suprathreshold voxel statistics in a cluster (or cluster mass), regardless of its theoretical tractability under the null hypothesis. These issues are illustrated by application to MRI data acquired from 18 adolescents with hyperkinetic disorder and 16 control subjects matched for age and gender.
authors: Department of Biostatistics and Computing, Institute of Psychiatry, King's College, University of London, UK. e.bullmore@iop.kcl.ac.uk
authors: E T
authors: ET
authors: Bullmore
authors: J
authors: J
authors: Suckling
authors: S
authors: S
authors: Overmeyer
authors: S
authors: S
authors: Rabe-Hesketh
authors: E
authors: E
authors: Taylor
authors: M J
authors: MJ
authors: Brammer
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001289:Attention Deficit Disorder with Hyperactivity / Q000473:pathology / Q000503:physiopathology; D001921:Brain / Q000033:anatomy & histology / Q000473:pathology*; D001931:Brain Mapping; D002648:Child; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015233:Models, Statistical