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As a first approximation, subtract the baseline difference from the post difference, use the reported post SDs and conduct a Student's t-test. John > John David Sorkin M.D., Ph.D. > Professor of Medicine > Chief, Biostatistics and Informatics > University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine > Baltimore VA Medical Center > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > (Phone) 410-605-7119 > (Fax) 410-605-7913 (Please call phone number above prior to faxing) > On Jan 25, 2016, at 8:35 AM, David Epstein <[log in to unmask]> wrote: > > Dear allstat > > I have published data at baseline and follow up from a clinical study, and want to know if the difference between the treatments is statistically significant. The groups A and B are defined according to whether re-treatment was needed at 6 weeks. The outcome measure is a continuous scale of patient symptoms where a larger number is a worse result. > > The data at baseline (before initial treatment) are: > Group A. N= 72, Mean = 22.08, SD = 12.38 > Group B. N=19, Mean = 24.7, SD = 12.63 > > At 6 weeks later: > Group A. N= 72, Mean = 11.97, SD = 11.18 > Group B. N = 19, Mean = 20.07, SD = 13.53 > > The authors state that the difference at 6weeks is 8.1 points, and the p-value is 0.01. However, Ive re-calculated this t-test by hand and the published p-value doesnt seem to take account that there is a difference at baseline. > > I dont have the individual data so cant adjust for any observed variables, but is it possible to do some kind of difference in difference test that at least takes account of the different mean baseline scores? > > Many thanks for your advice. > > -- > David Epstein > Departamento de Economía Aplicada > Universidad de Granada > Facultad de Ciencias Económicas y Empresariales > Campus de Cartuja, s/n, 18071. GRANADA > Teléfono:+34 958 249973 / 246258 > FAX: +34 958 244046 > email: [log in to unmask] > ============================== > Honorary Visiting Research Fellow > Centre For Health Economics > University of York > Heslington York Y010 5DD > email: [log in to unmask] > ============================== > You may leave the list at any time by sending the command > SIGNOFF allstat > > to [log in to unmask], leaving the subject line blank. Confidentiality Statement: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. You may leave the list at any time by sending the command SIGNOFF allstat to [log in to unmask], leaving the subject line blank.