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Sample size estimates for well-powered cross-sectional cortical thickness studies.

INTRODUCTION: 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. METHODS: 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). RESULTS: 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%. CONCLUSIONS: The derived model provides a simple tool for researchers to calculate how many subjects should be included in a well-powered cortical thickness analysis.

Pubmed ID: 22807270


  • Pardoe HR
  • Abbott DF
  • Jackson GD
  • Alzheimer's Disease Neuroimaging Initiative


Human brain mapping

Publication Data

November 23, 2013

Associated Grants

  • Agency: PHS HHS, Id: NIH-NINDS R37-31146
  • Agency: NINDS NIH HHS, Id: R37 NS031146
  • Agency: NIA NIH HHS, Id: U01 AG024904
  • Agency: NCATS NIH HHS, Id: UL1 TR000128

Mesh Terms

  • Adult
  • Anatomy, Cross-Sectional
  • Brain Mapping
  • Cerebral Cortex
  • Cohort Studies
  • Data Interpretation, Statistical
  • Female
  • Genetic Processes
  • Humans
  • Image Processing, Computer-Assisted
  • Magnetic Resonance Imaging
  • Male
  • Models, Neurological
  • Reproducibility of Results
  • Sample Size
  • Young Adult