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Re: st: Construct Null Datasets through Bootstrap Resampling
Thanks Michael,
After discussing this with our senior statistician today, I will
probably go with the replacement, since this is how they have done it
before in SAS. However, do you think that you could easily explain for
me how to keep groups together in the scramble code as well? Just if I
need to do it that way on a later occasion?
Best,
Erik Ingelsson
Quoting Michael Blasnik <[email protected]>:
One more difference between the approaches that you should recognize is
that bsample samples with replacement (a value from a given observation
can appear more than once) while the scramble program I wrote does not
-- it simply re-arranges the order. I'm not sure which is preferred
for your application.
If you end up wanting to sample without replacement (as scramble does)
but want to keep groups of variables together, a relatively modest
change to the scramble code would do the trick.
Michael Blasnik
----- Original Message ----- From: "Erik Ingelsson"
<[email protected]>
To: <[email protected]>
Sent: Thursday, November 30, 2006 11:37 PM
Subject: Re: st: Construct Null Datasets through Bootstrap Resampling
Dear Austin,
Well, actually Michael Blasniks suggestion was a bit closer to what
I first intended. But when looking at your suggestion and reading
some literate on multiple testing in genetic analyses, I realized
that I actually perhaps should not scramble all variables, but
rather keep them together in two groups (e.g. keeping var 1-4
togeter as in the orignal observation, but randomly pairing them
with var 5-8). For this, your solution worked perfectly. The next
step is to meet with our senior statistician and show him what I
got. He can tell which way to go, I hope.
Thanks a lot to both of you! I am impressed by the fast answers!
Erik Ingelsson
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---
Erik Ingelsson, MD, PhD
Current affiliation (until June 30, 2007):
Framingham Heart Study
73 Mt. Wayte Avenue, Suite 2
Framingham, MA 01702-5827
Phone: 508-935-3453
Fax: 508-626-1262
Cell: 508-202-8493
Permanent affiliation:
Uppsala University, Department of Public Health and Caring Sciences, Uppsala
Science Park, SE-751 85 Uppsala, SWEDEN.
Fax: +46-18-611 79 76
E-mail: [email protected]
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