JSM 2005 Online Program

Abstract #303053

This is the preliminary program for the 2005 Joint Statistical Meetings in Minneapolis, Minnesota. Currently included in this program is the "technical" program, schedule of invited, topic contributed, regular contributed and poster sessions; Continuing Education courses (August 7-10, 2005); and Committee and Business Meetings. This on-line program will be updated frequently to reflect the most current revisions.

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Activity Number:	47
Type:	Invited
Date/Time:	Sunday, August 7, 2005 : 4:00 PM to 5:50 PM
Sponsor:	Section on Statistical Computing
Abstract - #303053
Title:	Spatial Smoothing to Control Degrees of Freedom in fMRI Analysis
Author(s):	Keith J. Worsley*+
Companies:	McGill University
Address:	Department of Mathematics and Statistics, Burnside Hall, Montreal, International, PQ H3A 2K6, Canada
Keywords:
Abstract:	In the statistical analysis of fMRI data, the parameter of primary interest in the effect of a contrast of secondary interest is its standard error; of tertiary interest is the standard error of this standard error, or equivalently, the degrees of freedom (df). In a ReML (Restricted Maximum Likelihood) hierarchical mixed-effects analysis, we show how spatial smoothing of tertiary parameters increases the effective df (but not the smoothness of primary or secondary parameter estimates). The amount of smoothing can then be chosen in advance to achieve a target df, typically 100. We show how to do it at the first level of a hierarchical analysis by smoothing autocorrelation parameters, and at the second level by smoothing the ratio of random to fixed effects variances.

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