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Dear Allstat According to published data, the median concentration of a substance in blood was 306, with first and 3rd quartiles 207 and 423. The raw data are not published. We hypothesise that this concentration will double in a particular condition. How many patients & controls do we need? We would plan on using a Mann-Whitney test. The median is not equidistant between quartiles, so I don't know whether it's a good idea to guesstimate a mean & standard deviation, do a standard power calculation and inflate the sample size according to the asymptotic relative efficiency of the Mann Whitney. Best wishes Peter Hudson Dr. Peter R. Hudson Dept. of Biochemistry Maelor Hospital Wrexham, Wales, UK LL13 7TD Tel 01978 725867 Fax 01978 366520 [log in to unmask] Mae'r e-bost hwn ac unrhyw ffeiliau a drosglwyddir gydag ef yn gyfrinachol ac wedi'u bwriadu ar gyfer pwy bynnag y cyfeirir ef ato neu atynt. Os ydych wedi ei dderbyn drwy gamgymeriad yna gadewch i'r rheolwr systemau wybod drwy ddefnyddio'r manylion isod. Mae cynnwys yr e-bost hwn yn cynrychioli barn y sawl a enwir uchod, felly nid ydyw'n dilyn ei fod yn cynrychioli barn GIG Gogledd Ddwrain Cymru. Cofiwch fod yn ymwybodol ei bod yn bosibl y bydd disgwyl i Ymddiriedolaeth GIG Gogledd Ddwyrain Cymru roi cyhoeddusrwydd i gynnwys unrhyw ebost neu ohebiaeth a dderbynnir, yn unol ag amodau'r Ddeddf Rhyddid Gwybodaeth 2000. I gael mwy o wybodaeth am Ryddid Gwybodaeth, cofiwch gyfeirio at wefan Ymddiriedolaeth GIG Gogledd Ddwyrain Cymru ar www.newalesnhstrust.org.uk. Fodd bynnag, dymuna'r Ymddiriedolaeth roi ar ddeall y bydd unrhyw wybodaeth gyfrinachol neu bersonol ynglyn ag unigolion wedi'i ddiogelu o dan Ddeddf Diogelu Data 1998 This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager using the details below. The contents of this email represent the views of the individual(s) named above and do not necessarily represent the views of the North East Wales NHS Trust. Please be aware that, under the terms of the Freedom of Information Act 2000, the North East Wales NHS Trust may be required to make public the content of any emails or correspondence received. For futher information on Freedom of Information, please refer to the North East Wales NHS Trust website at www.newalesnhstrust.org.uk. However the Trust wishes to make it understood that information of a confidential and personal nature relating to individuals will be protected under the Data Protection Act 1998. For further assistance, please contact [log in to unmask]