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It has been proposed by El Emam et al. (ibid. vol.27 (7), 2001) that size should be taken into account as a confounding variable when validating object-oriented metrics. We take issue with this perspective since the ability to measure size does not temporally precede the ability to measure many of the object-oriented metrics that have been proposed. Hence, the condition that a confounding variable must occur causally prior to another explanatory variable is not met. In addition, when specifying multivariate models of defects that incorporate object-oriented metrics, entering size as an explanatory variable may result in misspecified models that lack internal consistency. Examples are given where this misspecification occurs.