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To the Editor: From their systematic review of observational studies, Dr Pronovost and colleagues¹ concluded that intensive care units (ICUs) with mandatory intensivist consultation or care had lower patient mortality and shorter length of stay than did ICUs with either no intensivists or optional intensivist care. We are concerned, however, that observational studies are easily biased (eg, selection, information, and confounding bias), which can compromise internal validity.² We also are concerned that the authors chose to include only English-language publications, thus excluding 294 articles with potentially relevant information.

Finally, given the heterogeneity of the studies, it may not be appropriate to combine them into a summary measure of the effect size.

Ruiz García, MD
Unidad de Hospitalización Domiciliara
Hospital La Fe
Valencia, Spain

Jose María Tenias, MD
Servicio de Medicina Preventiva
Hospital Lluis Alcanyis, Xàtiva
Valencia

1. Pronovost PJ, Angus DC, Dorman T, Robinson KA, Dremsizov TT, Young TL. Physician staffing patterns and clinical outcomes in critically ill patients: a systematic review. JAMA. 2002;288:2151-2162. FREE FULL TEXT 2. Egger M, Smith GD, Schneider M. Systematic reviews of observational studies. In: Egger M, Smith GD, Altman DG, eds. Systematic Reviews in Health Care: Goal Analysis in Context. London, England: BMJ Publishing Group; 2001:211-227.

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2003;289:985-986.