The Why and How of Z Scores

      The use of echocardiographic measurements to detect disease and predict outcomes can be confounded by a number of nondisease factors, including the effect of body size, that contribute to the variance of these measurements. The process of normal growth is associated with a nearly 200-fold increase in normal left ventricular end-diastolic volume (EDV) from premature infants up to large adolescents, making it imperative to account for changes in body size in pediatrics. Although this issue is often ignored in adult echocardiography, the sensitivity and specificity of parameters of left ventricular size are significantly improved when adjustment for body size in adults is performed.
      • De Simone G.
      • Daniels S.R.
      • Devereux R.B.
      • Meyer R.A.
      • Roman M.J.
      • De Divitiis O.
      • et al.
      Left ventricular mass and body size in normotensive children and adults: assessment of allometric relations and impact of overweight.
      The article by Mawad et al.
      • Mawad W.
      • Drolet C.
      • Dahdah N.
      • Dallaire F.
      A review and critique of the statistical methods used to generate reference values in pediatric echocardiography.
      in this issue of JASE addresses an important aspect of this process, although it is likely a topic that is unfamiliar to most echocardiographers, even those in pediatric cardiology who rely heavily on Z scores. The concept of Z scores itself is often unfamiliar to adult echocardiographers.
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      Linked Article

      • Correction
        Journal of the American Society of EchocardiographyVol. 26Issue 4
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          In the article, “The Why and How of Z Scores,” by Colan, J Am Soc Echocardiogr 2013;26:38-40, the second sentence in the first paragraph on page 40 contains an error. The correct sentence should be “We undertook a comprehensive exploration of this issue5 and found that both theoretical considerations and empirical observations indicated that BSA is superior to height or weight alone as an allometric variable in normal subjects, that the Haycock formula7 for BSA was superior to the other published formulas, and that exponential equations of the form Y = α x BMIb + c provided the best descriptor for all anatomic cardiac measurements.
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