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Thomas B. Newman, MD, MPH
University of California, San Francisco

JAMA. 1995;274(13):1013.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.

—Twelve years ago in an article entitled "IfNothing Goes Wrong, Is Everything All Right?" Drs Hanley and Lippman-Hand¹ provided a helpful rule of thumb for interpreting numerators of 0. They showed that if 0 events are observed in N trials, the upper limit of the 95% confidence interval (CI) for the frequency of events is approximately 3/N. Thus, if there are no deaths among 50 patients treated with a new medication, the upper limit of the 95% CI for the risk of death is about 3/50, or 6%. On the other hand, if no deaths occur in a study of 1000 patients, the upper limit of the 95% CI for the mortality rate is 3/1000, or 0.3%.

I have found that similar approximations work for other small numerators and that they can be a helpful shortcut when scanning journal articles. In each case, as the denominator . . . [Full Text PDF of this Article]

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