BE parallel design [General Sta­tis­tics]

posted by Jaime_R – Barcelona, 2007-04-03 17:41 (5409 d 10:31 ago) – Posting: # 619
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» Thank you. While using raw data and log data, I have significantly different results.

That's quite common using transformations on data.
I hope you have a statistical protocol in place, and are not playing around to see which results are meeting your expectations. ;-)

» In case of the parallel design, I calculate the ratio taking the mean from one group and the mean of the other group for the raw data and log of the mean from one group and log of the mean from another gruop. Am I true?

I guess, you are talking of untransformed analysis first and transfomed analysis second?

Let's concentrate only on the transfomed analysis (because this is the one you will need).
  1. Calculate the log (Y1,Y2,...,Yn) of all individual values (X1,X2,...,Xm), where n = number of subjects under test and m = number of subjects under reference
  2. Calculate the arithmetic means form log transfomed data (Y) for the two treatments (YT and YR)
  3. If you want you can antilog these means (= geometric means of the original data)
  4. Calculate the SDs for the two treatments (SDT, SDR)
  5. Calculate the total variance S^2 = [(n-1)*SDT^2 + (m-1)*SDR^2]/(n+m-2)
  6. Calculate the difference Delta = YT - YR
  7. Calculate the point estimate by taking the antilog of Delta
  8. Calculate the upper/lower confidence limit as Delta + t(0.05,n+m-2)*S^2
  9. Calculate the antilogs of these confidence limits

Regards, Jaime

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