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Re: st: sampsi


From   "Eurich, Dean" <deurich@ualberta.ca>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: sampsi
Date   Fri, 19 Aug 2011 13:09:37 -0600

Hi Phil,

Sorry for the confusion. We are not really interested in the longitudinal
changes over the longer term (I.e., 5 years). What we want to do do is
basically - Does very short term changes in brain function at time of
diagnosis (I.e., 8 weeks) predict 5 yr mortality.  So in a sense the 8
week change score a "baseline value". We are not interested if the
patients continue to decline or not.

Hope that makes sense.

Thanks again.

Dean

On 11-08-19 12:57 PM, "Phil Schumm" <pschumm@uchicago.edu> wrote:

>On Aug 19, 2011, at 9:07 AM, Eurich, Dean wrote:
>> The study is really two separate studies. The first is what sample size
>>do we require to observe a 2% change in magnetic imaging brain scans for
>>controls and ALS patients over an 8 month period.
>
>
>To clarify, the calculation you originally asked about involved detecting
>a difference in the mean change (in your imaging outcome) between ALS and
>controls.  IOW, it appears that you want to demonstrate that ALS patients
>on average decline faster than controls (who I presume are matched on
>age, gender, etc.).  This is consistent with the baseline measurements
>you showed (where the average for the controls was higher than for those
>with ALS), but I presume you want to show/estimate the difference
>longitudinally rather than just cross-sectionally.  You don't need to
>explain the rationale for doing this -- I just wanted to make sure that
>we were on the same page (your sentence above is a bit ambiguous WRT
>this).
>
>
>-- Phil
>
>
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