The Hypertension Prevention Trial-Reply

In Reply.—Since blood pressure is a variable that is influenced by a host of factors and its measurement is associated with errors, the issue in a trial such as the Hypertension Prevention Trial (HPT) is not whether there is variability and error, but rather the influence they have on the results observed. Clearly, the greater the variability of a measure, the more difficult it is to find differences among the treatment groups because of a lack of precision of the measurement. Recognition of this is the reason the investigators in the HPT devoted considerable time and resources to standardization of the measurement process by training blood pressure observers, by use of random zero sphygmomanometers, and by continuous monitoring of the measurement process.¹ Indeed, one might argue that the observation of blood pressure differences among the treatment groups is even more noteworthy because it emerges in spite of the