title: Reliability and statistical power analysis of cortical and subcortical FreeSurfer metrics in a large sample of healthy elderly.
abstract: FreeSurfer is a tool to quantify cortical and subcortical brain anatomy automatically and noninvasively. Previous studies have reported reliability and statistical power analyses in relatively small samples or only selected one aspect of brain anatomy. Here, we investigated reliability and statistical power of cortical thickness, surface area, volume, and the volume of subcortical structures in a large sample (N=189) of healthy elderly subjects (64+ years). Reliability (intraclass correlation coefficient) of cortical and subcortical parameters is generally high (cortical: ICCs>0.87, subcortical: ICCs>0.95). Surface-based smoothing increases reliability of cortical thickness maps, while it decreases reliability of cortical surface area and volume. Nevertheless, statistical power of all measures benefits from smoothing. When aiming to detect a 10% difference between groups, the number of subjects required to test effects with sufficient power over the entire cortex varies between cortical measures (cortical thickness: N=39, surface area: N=21, volume: N=81; 10mm smoothing, power=0.8, α=0.05). For subcortical regions this number is between 16 and 76 subjects, depending on the region. We also demonstrate the advantage of within-subject designs over between-subject designs. Furthermore, we publicly provide a tool that allows researchers to perform a priori power analysis and sensitivity analysis to help evaluate previously published studies and to design future studies with sufficient statistical power.
authors.affiliation: Department of Neuropsychology, Institute of Psychology, University of Zurich, Zurich, Switzerland; University Research Priority Program "Dynamics of Healthy Aging", University of Zurich, Zurich, Switzerland. Electronic address: f.liem@psychologie.uzh.ch.
authors.forename: Franziskus
authors.initials: F
authors.lastname: Liem
authors.affiliation: University Research Priority Program "Dynamics of Healthy Aging", University of Zurich, Zurich, Switzerland; International Normal Aging and Plasticity Imaging Center (INAPIC), University of Zurich, Zurich, Switzerland.
authors.forename: Susan
authors.initials: S
authors.lastname: Mérillat
authors.affiliation: University Research Priority Program "Dynamics of Healthy Aging", University of Zurich, Zurich, Switzerland; International Normal Aging and Plasticity Imaging Center (INAPIC), University of Zurich, Zurich, Switzerland.
authors.forename: Ladina
authors.initials: L
authors.lastname: Bezzola
authors.affiliation: University Research Priority Program "Dynamics of Healthy Aging", University of Zurich, Zurich, Switzerland; International Normal Aging and Plasticity Imaging Center (INAPIC), University of Zurich, Zurich, Switzerland.
authors.forename: Sarah
authors.initials: S
authors.lastname: Hirsiger
authors.affiliation: Department of Psychological Methods, Evaluation, and Statistics, Institute of Psychology, University of Zurich, Zurich, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Philipp
authors.affiliation: Department of Radiology, University of WA, Seattle, United States.
authors.forename: Tara
authors.initials: T
authors.lastname: Madhyastha
authors.affiliation: Department of Neuropsychology, Institute of Psychology, University of Zurich, Zurich, Switzerland; University Research Priority Program "Dynamics of Healthy Aging", University of Zurich, Zurich, Switzerland; International Normal Aging and Plasticity Imaging Center (INAPIC), University of Zurich, Zurich, Switzerland; Department of Special Education, King Abdulaziz University, Jeddah, Saudi Arabia.
authors.forename: Lutz
authors.initials: L
authors.lastname: Jäncke
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D001921:Brain / Q000473:pathology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards*; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging / Q000379:methods* / Q000592:standards*; D015203:Reproducibility of Results; D012984:Software
keywords: Cortical surface area; Cortical thickness; Cortical volume; Subcortical volume; Surface-based morphometry