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I'm reading the results of an individual patient data (IPD) meta-analysis. The outcomes of the study is expressed in standard deviations (SD's). Comparisons between groups are stated as 0,23 (95% CI 0.15-0.33), SD 0.34, etc. I can't grasp how to interpretate this. Can somebody help?

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The point estimate is 0.23. Any sensible confidence interval for the parameter should include 0.23. The given confidence interval goes from [0.15, 0.33]. So 0.23 is near the middle. Generally 95% confidence intervals are reported but the confidence level is not stated. So you can't be sure, 90% and 99% are also common. The part where you wrote 0.34 SD's etc. is missing something. So I do not see how to interpret it. I might be able to with a more complete quotation. An estimate such as 0.23 (in your case is often given with the CI represented as + or - k standard errors (i.e. standard error is standard deviation of the estimate). But it may be that the estimate and the confidence interval are being expressed in units of standard deviations.

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Yes, the estimates are expressed in units of standard deviations.I copied a piece of the conclusion:, 0.16 (95% CI, 0.07-0.25), and 0.15 (95% CI, 0.07-0.24) SDs lower than sham controls for back and neck pain, osteoarthritis, and chronic headache, respectively; the effect sizes in comparison to noacupuncture controls were 0.55 (95% CI, 0.51-0.58), 0.57 (95% CI, 0.50-0.64), and 0.42 (95% CI, 0.37-0.46) SDs. These results were robust to a variety of sensitivity analysis.... – johanna Sep 18 '12 at 18:44
I understand the confidence intervals and the point estimates meaning, but don't get the meaning of units of SD's – johanna Sep 18 '12 at 18:47
@johanna. That is simple. You have a value x and a standard deviation y where x and y are in the same units then x/y puts x into units of standard deviations. So if in the original units the standard deviation is 0.23 then X/0.23 expresses the quantity x in standard deviation units. If you want to see all the inteval endpoints and estimates in the original units just multiple by the standard deviation (in my example you multiple by 0.23). Is the standard deviation given in the study article? – Michael Chernick Sep 18 '12 at 19:04
Oh, my..My brain can't take this at once. I have to check the article once more. – johanna Sep 18 '12 at 19:20
One more citation:To give an example of what these effect sizes mean in real terms, a baseline pain score on a 0 to 100 scale for a typical RCT might be 60. Given a standard deviation of 25, follow- up scores might be 43 in a noacupuncture group, 35 in a sham acupuncture group, and 30 in patients receiving true acupuncture. If response were defined in terms of a pain reduction of 50% or more, response rates would be approximately 30%, 42.5%, and 50%, respectively. – johanna Sep 18 '12 at 19:58
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