Hi Professor Thomas,Thank you for introducing me to the modified SWE toolboxSay, I am trying to see whether two groups differ in their rate of change in grey matter volumes over 2 ( mean follow up is about 3 years), and also ask whether this rate of change correlate with other variables.The design.sub would look something like
Order of Scan Visit Number Group 1 1 1 1 2 1 2 1 1 2 2 1 3 1 0 3 2 0 4 1 0 4 2 0 Since there shouldn't be subject specific information in the design matrix, I am not quite sure how to proceed.If I want to look at the interaction effect of time on group, while also correcting for age, would the matrix below be OK? ? In this example, the age is fixed at baseline. Should it be changing across time as well, such that the 2nd age for each is baseline age + scan interval years?
Age 41 41 30 30 51 51 40 40 Can you teach me how to create the contrast for this instance?Thank you.Best Regards,ShaneOn Sunday, January 19, 2020, 10:24:02 PM GMT, Thomas Nichols <[log in to unmask]> wrote:Hi Shane,There are only some very specific mixed model analyses that PALM can do. Voxelwise, LME models are computationally intensive and can also have problems with convergence failures. I would suggest instead a related approach, using a sandwich estimator approach. In this approach, you only need to model the population effects (e.g. you don't have to specify if there are random intercepts or random slopes), ordinary least squares is used and then the repeated measures/longitudinal covariance is accounted for in the calculation of the standard error.While I initially developed this as a SPM toolbox http://www.nisox.org/Software/SwE/ it is now available in FSL as "swe" https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/Swe .If you give swe a try, please let me and I'll be happy to help you get started.-TomHi Anderson,I have been using MATLAB for doing LME on ROI longitudinal data but now I would like to explore this using PALM. Apologies if I have missed the details but I can't see any LME option on the website. Specifically I want to test whether a variable is correlated with grey matter changes over time ( 2 time points), using random intercept for each subject while correcting for age and IQ. Any advice on how to implement this ?Thank you.Best Wishes,Shane
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https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=FSL&A=1--__________________________________________________________Thomas Nichols, PhDProfessor of Neuroimaging StatisticsNuffield Department of Population Health | University of Oxford
Big Data Institute | Li Ka Shing Centre for Health Information and Discovery
Old Road Campus | Headington | Oxford | OX3 7LF | United Kingdom
T: +44 1865 743590 | E: [log in to unmask]
W: http://nisox.org | http://www.bdi.ox.ac.uk
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