Dear Sir:Zimmermannetal(1)showed,in6–12-y-oldSwisschildren,thatthe 95th BMI percentile of the Centers for Disease Control andPrevention (CDC) cutoffs have a higher sensitivity than do the In-ternational Obesity Task Force (IOTF) obesity cutoffs to detectobesitybasedonskinfoldthicknesses.TheyconcludedthattheCDCcutoffs are superior to the IOTF cutoffs, but this conclusion is mis-leading for 2 reasons.ItistruethatsensitivityishigherwiththeCDCcutoffs;however,ZimmermanetaldidnothighlightthehigherspecificityoftheIOTFcutoffs. In Table 5 of Zimmerman et al’s article, it shows that thespecificitiesfordetectingobesitywiththeCDCandtheIOTFcutoffsare 97.3 and 98.6, respectively, in girls, and 96.9 and 99.5, respec-tively,inboys.So,thefalse-positiverateistwiceashighingirlsand 6 times as high in boys with the CDC cutoffs.This tradeoff between sensitivity and specificity is well-known,andfocusingononewhileneglectingtheotherisnotthebestwaytocompare cutoffs. The reason why the IOTF obesity cutoffs havelowersensitivity(andhigherspecificity)issimplybecausetheyaremore extreme, as the authors point out, which leads to lower prev-alence rates of obesity (2, 3).The second concern is that the gold standard used by Zimmer-mannetal,percentagebodyfatbasedonskinfoldthicknesses,issetat the 95th percentile of the distribution, which matches the corre-sponding CDC cutoffs but is lower than the IOTF cutoffs. If thedefinition of obesity had been based on the 99th percentile for per-centage body fat, the comparative results for sensitivity and speci-ficitywouldhavebeendifferent,ie,thesensitivityoftheIOTFcutoffwould have been much higher. In this instance, as in others, it isimportant to compare like with like.Giventhecontinuingriseintheprevalenceofchildobesity,thereis also some benefit in having a more extreme cutoff available tofocusontheextremegroupofchildrenmostatriskofobesity-relatedcomplications, such as those with type 2 diabetes (4).