I am trying to run a power calculation for a randomized control trial. For this I need a mean and standard deviation for our 'baseline'. There are papers out there which would have a mean and standard deviation, but what we would want would be to use their final outcomes as our baseline. In other words, these papers applied treatment $A$. I would like to apply treatment $B$ on top of treatment $A$, so treatment $A$ outcomes will be my new baseline.

In looking at their results tables, I can find the mean and SD of their baseline, plus the coefficient of the effect and that coefficient's SD. To find the new mean of my baseline, I would add the coefficient to the mean. However, is there a way to back out the SD of the new mean from the information I have from these papers?

To give an example: one paper has the mean in control as 5847 (SD=16784). The change of the mean under treatment $A$ is 267 (SD=527). So my new baseline would be 5847 + 267 = 6114. But would there be any way of getting this SD without the data? (Almost all of it is not available publicly.)

Thanks so much!

  • $\begingroup$ Hi and welcome to the site! Could you clarify what the numbers from the papers are (in the example)? What are the variables and what is meant by "coefficient"? Also, what do the numbers within the parentheses denote? Thank you. $\endgroup$ – COOLSerdash Jul 23 '13 at 20:51
  • $\begingroup$ Thanks so much! My colleague recommended that I try this forum. $\endgroup$ – user2612075 Jul 23 '13 at 20:56
  • $\begingroup$ You're welcome here and I hope you get some useful answers to your question! $\endgroup$ – COOLSerdash Jul 23 '13 at 20:58
  • $\begingroup$ The numbers in the example are as follows: Baseline mean (before treatment A) is 5847, and baseline s.d. is 16784. The coefficient is the change in the mean with the presence of the dummy (in this case, treatment A). Does that make sense? $\endgroup$ – user2612075 Jul 23 '13 at 21:02
  • $\begingroup$ Sorry. That is the standard deviation of the change (267). $\endgroup$ – user2612075 Jul 23 '13 at 21:24

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