Hi Lea, I'm cc'ing the list so that others can benefit.
On 06/13/2018 12:28 PM, Backhausen, Lea wrote: > > > Hey Doug, > > Thanks for your helpful suggestions on Monte Carlo simulation and > permutation you gave in the Mailing List! > > I have some follow-up questions, also regarding your recently > published paper about false positive rates > (https://www.sciencedirect.com/science/article/pii/S1053811917310960). > > 1) Concerning Monte Carlo simulation where you said even 1000 > iterations would be okay: What will the difference be between 1000 and > 10,000 iterations? I read in the tutorial that >5000 are recommended? > This has to do with the precision of the cluster p-value Since you are doing a simulation, the p-value is subject to sampling error. If you look in the output file, you will see that I give 95% confidence intervals for the p-value, so as long as the high range is less than .05, then it should be ok. I think 1000 is probably fine. > > 2) In your paper you write that permutation requires that data is > exchangeable across subjects and that age effects may be a problem. In > our study we want to compare adolescent patients with ADHD and conduct > disorder with typically developing adolescents. In this context, data > would not be exchangeable across subjects, right? Could we still use > permutation? > Exchangeability is a very complicated subject and not very intuitive. It is too complicated to get into here. I suggest reading up on it a little. It does not mean that you can swap groups without there being any effect. > > 3) When using the CFT thresholds with Monte Carlo simulation you > recommend in your paper, do you still only report clusters with > CWP<.05 or is the CWP less important when using stricter thresholds? > Generally, CWP must be less than 0.05 for publication. Sometimes people will show results with more liberal p-values (eg, 0.1) to show "trends". It all depends on what you can get past your reviewers:). doug > > Thank you so much for your input! > > Best > > Lea Backhausen > > ------------------------------ > > Lea Backhausen > > Research Assistant > > Department of Child and Adolescent Psychiatry, Faculty of Medicine of > the TU Dresden, Germany > http://www.uniklinikum-dresden.de <http://www.uniklinikum-dresden.de/> > _______________________________________________ Freesurfer mailing list [email protected] https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
