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Title: Sample size estimates for well-powered cross-sectional cortical thickness studies.
Austin Authors: Pardoe, Heath R;Abbott, David F ;Jackson, Graeme D 
Institutional Author: Alzheimer's Disease Neuroimaging Initiative
Affiliation: Brain Research Institute, Florey Neuroscience Institutes, Melbourne Brain Centre, Austin Hospital, Heidelberg, Victoria, Australia
Department of Medicine, The University of Melbourne, Victoria, Australia
Issue Date: 17-Jul-2012
Publication information: Human Brain Mapping 2012; 34(11): 3000-9
Abstract: Cortical thickness mapping is a widely used method for the analysis of neuroanatomical differences between subject groups. We applied power analysis methods over a range of image processing parameters to derive a model that allows researchers to calculate the number of subjects required to ensure a well-powered cross-sectional cortical thickness study.0.9-mm isotropic T1 -weighted 3D MPRAGE MRI scans from 98 controls (53 females, age 29.1 ± 9.7 years) were processed using Freesurfer 5.0. Power analyses were carried out using vertex-wise variance estimates from the coregistered cortical thickness maps, systematically varying processing parameters. A genetic programming approach was used to derive a model describing the relationship between sample size and processing parameters. The model was validated on four Alzheimer's Disease Neuroimaging Initiative control datasets (mean 126.5 subjects/site, age 76.6 ± 5.0 years).Approximately 50 subjects per group are required to detect a 0.25-mm thickness difference; less than 10 subjects per group are required for differences of 1 mm (two-sided test, 10 mm smoothing, α = 0.05). Sample size estimates were heterogeneous over the cortical surface. The model yielded sample size predictions within 2-6% of that determined experimentally using independent data from four other datasets. Fitting parameters of the model to data from each site reduced the estimation error to less than 2%.The derived model provides a simple tool for researchers to calculate how many subjects should be included in a well-powered cortical thickness analysis.
Gov't Doc #: 22807270
DOI: 10.1002/hbm.22120
Journal: Human brain mapping
Type: Journal Article
Subjects: MRI
cortical thickness
power analysis
study design
Anatomy, Cross-Sectional.methods
Brain Mapping.methods
Cerebral Cortex.anatomy & histology
Cohort Studies
Data Interpretation, Statistical
Genetic Processes
Image Processing, Computer-Assisted
Magnetic Resonance Imaging
Models, Neurological
Reproducibility of Results
Sample Size
Young Adult
Appears in Collections:Journal articles

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