The guideline is for prevalence of wasting. Prior to about 2006 this meant prevalence of wasting by WHZ <- 2 using the NCHS reference population or bilateral pitting oedema. From 2006 this (increasingly) means WHZ < -2 using the WGS reference population or bilateral pitting oedema. In 2006, MUAC < 110 mm was promoted as an independent case-definition for SAM. This was confirmed in 2008 and the case-defining threshold for SAM increased to 115 mm so as to include more (usually older) WHZ < -3 children. This has not been universally adopted, In Ethiopia (e.g.) 110 mm is still used and MSF have used 120 mm in some CMAM-type programs. There is also been an adoption of MUAC case-definitions for GAM in some countries (e.g. 120 mm in Ethiopia for some supplementary programs (EOS program) and MUAC < 125 mm in many other countries. Despite these changes the 15% threshold has stayed. This is "15% however defined". As in your original message ... WHZ <- 2 and WHM < 80% are different definitions selecting different children. Don't forget bilateral pitting oedema in case-definitions. In short ... 15% wasting is 15% wasting. It does not make a difference which case-definition you use. It can be argued that the changes (i.e. NCHS replaced by WGS, MUAC added) are refinements / improvements. I would use MUAC case-definitions because the many problems with W/H but this is is not a universally agreed position. If you search these forums you will finds this matter has been discussed previously (e.g. [url=http://www.en-net.org/question/40.aspx]here[/url], [url=http://www.en-net.org/question/206.aspx]here[/url] and probably elsewhere. I hope this helps.