Power calculation for cohort studies with improved estimation of expected numbers of deaths

Summary This paper focuses on improving the accuracy of sample size calculations for cohort studies by careful calculation of the expected number of deaths in the population, taking into account either prior information or realistic assumptions about variables which may affect the mortality or incidence. Sometimes small changes in the assumptions can dramatically alter the expected numbers and may necessitate modifications in the design of the study. Possible modification include extension of the follow-up time, and recognition that the real strength of the study may lie in the potential for pooling several similar studies. The problem will be discussed with reference to two examples of occupational cohort studies where differing prior information was available.

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Zusammenfassung Diese Arbeit beschäftigt sich mit der Genauigkeit der Berechnung des Stichprobenumfangs in Kohortenstudien, wenn detaillierte Berechnungen für die erwartete Zahl der Verstorbenen berücksichtigt werden. Dies kann entweder durch die Ausnutzung vorhandener Informationen oder durch realistische Annahmen über die Faktoren, die Mortalität oder Inzidenz beeinflussen, geschehen. Schon kleine Unterschiede in diesen Annahmen kann die erwartete Zahl der Verstorbenen erheblich verändern und es notwendig machen, das Design einer Studie zu verändern. Solche Modifikationen bestehen z.B. in der Verlängerung der Follow-up Zeit der Studie oder in der Einsicht, dass es nötig ist, Daten aus mehreren Studien zusammenzufassen. Die Probleme werden anhand von zwei Beispielen aus dem Bereich der Berufsepidemiologie diskutiert.

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Résumé Cet article concerne la précision des estimations de taille d'échantillons pour les études de cohortes. Le calcul précis du nombre de décès attendus dans la population prend en compte les variables susceptibles d'affecter la mortalité ou l'incidence, provenant soit d'une connaissance préalable, soit d'hypothèses réalistes. De modestes changements d'hypothèses peuvent parfois altérer de façon substantielle les nombres attendus et nécessiter des modifications dans le protocole de l'étude. Parmi les modifications possibles, il faut citer la prolongation du temps de suivi de l'étude ainsi que le constat que la valeur réelle de l'étude pourrait reposer sur la possibilité de mise en commun de plusieurs études similaires. Le problème est discuté à l'aide de deux exemples d'études de cohortes professionnelles pour lesquelles différentes informations préalables sont disponibles.

     

A comparison of tympanic thermometer readings to pulmonary artery catheter core temperature recordings

The purpose of this study was to determine the accuracy of FirstTemp (Intelligent Medical Systems, Carlsbad, CA) tympanic thermometer readings compared with core body temperatures obtained via pulmonary artery catheter (PAC). Five measurements were obtained on 19 cardiovascular surgery patients. Tympanic thermometer measurements tended to be higher than PAC measurements. However, most of the differences were not clinically significant. Differences found between right and left ear measurements were most likely due to poor measurement technique. When the correct technique is used, nurses can be confident that tympanic temperature readings are clinically accurate.     

What Are American Children Eating? Implications for Public Policy

As the health and demographic profile of the U.S. population changes, the food consumption patterns of American children have also changed. This review is organized around a series of policy issues looking at these new food consumption patterns, their relationship to the Dietary Guidelines, and their impact on children's health.     

Prospective trial of supranormal values as goals of resuscitation in severe trauma.

We prospectively tested the effect of the early postinjury attainment of supranormal values of cardiac index (> or = 4.52 L/min per square meter), oxygen delivery (> or = 670 mL/min per square meter), and oxygen consumption (> or = 166 mL/min per square meter) on outcome in traumatized patients with an estimated blood loss of 2000 mL or more. The goals in control patients were to attain normal values for all hemodynamic measurements. During the 6-month period, 33 protocol patients and 34 control patients with similar vital signs, estimated blood losses, and severity of injuries were enrolled in the study. Eight (24%) protocol patients died, while 15 (44%) control patients died. The protocol patients had fewer mean (+/- SEM) organ failures per patient (0.76 +/- 1.21 vs 1.59 +/- 1.60), shorter stays in the intensive care unit (5 +/- 3 vs 12 +/- 12), and fewer mean days requiring ventilation (4 +/- 3 vs 11 +/- 10) than did the control patients (P < .05 for each). We conclude that attaining supranormal circulatory values improves survival and decreases morbidity in the severely traumatized patient.