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One minor correction, fixed effects FEAT also uses weighted OLS. On Wed, Feb 20, 2013 at 9:45 AM, MCLAREN, Donald <[log in to unmask]> wrote: > The combined weights are whatever you tell the program. If you use 1s > and -1s, then your estimate will be N times as great as 1 run. I'd > recommend using 1/N and -1/N. This will create the average contrast > across runs. You could also decide to weight each run based on the > number of trials. > > In FSL, the weighting is based on the variance - not the beta. It will > deweight betas with high variance estimates. It's only used with FLAME > and other models, not the OLS model. > > Best Regards, Donald McLaren > ================= > D.G. McLaren, Ph.D. > Research Fellow, Department of Neurology, Massachusetts General Hospital and > Harvard Medical School > Postdoctoral Research Fellow, GRECC, Bedford VA > Website: http://www.martinos.org/~mclaren > Office: (773) 406-2464 > ===================== > This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED > HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is > intended only for the use of the individual or entity named above. If the > reader of the e-mail is not the intended recipient or the employee or agent > responsible for delivering it to the intended recipient, you are hereby > notified that you are in possession of confidential and privileged > information. Any unauthorized use, disclosure, copying or the taking of any > action in reliance on the contents of this information is strictly > prohibited and may be unlawful. If you have received this e-mail > unintentionally, please immediately notify the sender via telephone at (773) > 406-2464 or email. > > > On Wed, Feb 20, 2013 at 8:14 AM, Glen Lee <[log in to unmask]> wrote: >> Dear SPM experts, >> >> For the 1st level GLM, I've been modeling each run separately as opposed to >> concatenating all the runs. >> Obviously I get more beta values that are generated by each run. However, >> when I create the contrast images (condition A vs. condition B), I then >> combine betas corresponding to the same condition across the entire runs. >> >> I've been assuming that this fixed analysis would be just as simple as an >> independent t-test for comparing betas in two different conditions without >> any other complicate procedures such as giving a greater weight to the >> higher beta value (I heard that this is the way how FSL does). >> >> If anybody knows how this works out, please help me. >> >> thanks in advance, >> Glen >> >> >> >> >> >> >>