title: Are power calculations useful? A multicentre neuroimaging study.
abstract: There are now many reports of imaging experiments with small cohorts of typical participants that precede large-scale, often multicentre studies of psychiatric and neurological disorders. Data from these calibration experiments are sufficient to make estimates of statistical power and predictions of sample size and minimum observable effect sizes. In this technical note, we suggest how previously reported voxel-based power calculations can support decision making in the design, execution and analysis of cross-sectional multicentre imaging studies. The choice of MRI acquisition sequence, distribution of recruitment across acquisition centres, and changes to the registration method applied during data analysis are considered as examples. The consequences of modification are explored in quantitative terms by assessing the impact on sample size for a fixed effect size and detectable effect size for a fixed sample size. The calibration experiment dataset used for illustration was a precursor to the now complete Medical Research Council Autism Imaging Multicentre Study (MRC-AIMS). Validation of the voxel-based power calculations is made by comparing the predicted values from the calibration experiment with those observed in MRC-AIMS. The effect of non-linear mappings during image registration to a standard stereotactic space on the prediction is explored with reference to the amount of local deformation. In summary, power calculations offer a validated, quantitative means of making informed choices on important factors that influence the outcome of studies that consume significant resources.
authors.affiliation: Brain Mapping Unit, Department of Psychiatry, University of Cambridge, Cambridge, United Kingdom; Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, United Kingdom; Cambridge and Peterborough Foundation NHS Trust, Cambridge, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Suckling
authors.forename: Julian
authors.initials: J
authors.lastname: Henty
authors.forename: Christine
authors.initials: C
authors.lastname: Ecker
authors.forename: Sean C
authors.initials: SC
authors.lastname: Deoni
authors.forename: Michael V
authors.initials: MV
authors.lastname: Lombardo
authors.forename: Simon
authors.initials: S
authors.lastname: Baron-Cohen
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
authors.forename: Anna
authors.initials: A
authors.lastname: Barnes
authors.forename: Bhismadev
authors.initials: B
authors.lastname: Chakrabarti
authors.forename: Cinly
authors.initials: C
authors.lastname: Ooi
authors.forename: Meng-Chuan
authors.initials: MC
authors.lastname: Lai
authors.forename: Steven C
authors.initials: SC
authors.lastname: Williams
authors.forename: Declan G M
authors.initials: DG
authors.lastname: Murphy
authors.forename: Edward
authors.initials: E
authors.lastname: Bullmore
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002138:Calibration; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D017711:Nonlinear Dynamics; D018579:Patient Selection; D018401:Sample Size; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: multicentre; neuroimaging; power calculations