One of my readers has asked for a 'how-to-do-it' about comparing data sets using 'mirror design'. I can't find anything on Medline or similar, nor in any statistical textbooks, and Google keeps giving mewebsites of data storage companies. Can anyone help? Chrissy Allott (Librarian) Healthcare Library Prospect Park Hospital Honey End Lane Reading RG30 4EJ Tel: 0118 960 5015 Fax: 0118 960 5014 Did you know you can now access over 1000 full text journals, The Cochrane Library and Clinical Evidence together with other high quality sources of information via the National electronic Library for Health. DISCLAIMER: The information contained in this message or any of its attachments may be privileged and confidential and intended for the exclusive use of the addressee. The views expressed may not be official policy but the personal views of the originator. If you are not the addressee any disclosure, reproduction, distribution, other dissemination or use of this communication is strictly prohibited. If you received this message in error please return it to the originator. All messages sent by this organisation are checked for viruses using the latest anti virus products. This does not and can not however guarantee that a virus has not been transmitted. Please therefore ensure that you take your own precautions for the detection and eradication of viruses.