I thank you for your suggestion, but I don't see how it helps answer my question.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) >>> "Justice Moses K. Aheto" <[log in to unmask]> 12/29/14 6:26 AM >>> Hi John, I think you should have a look at pooled standard errors which you can use to estimate the combined standard error for the two samples. Example below: SEx1-x2 = sqrt [ s21 / n + s22 / m ] Hope this helps. Cheers Kind regards ***************************************** Justice Moses K. Aheto PhD Candidate in Medicine (United Kingdom) MSc Medical Statistics (United Kingdom) BSc Statistics (Ghana) HND Statistics (Ghana) Chief Executive Officer Statistics and Analytics Consultancy Services Ltd. E-mail: [log in to unmask] Skype: jascall12 Mobile: +447417589148. On Monday, December 29, 2014 11:12 AM, John Sorkin <[log in to unmask]> wrote: How can I compute the SE (standard error) of the concatenation of two samples? Assume sample 1 has n observations, sample 2 has m observations The concatenation of sample 1 with sample 2 would have n+m observations. If I know the mean of sample 1 = m1, and SE sample 1=se1, the mean of sample 2 = m2, and SE sample 2=se2, can I use n, m1, se1, m, m2, se2 to compute the SE? Thank you, 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) 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. 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.