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J Thorac Cardiovasc Surg 1999;118:973
© 1999 Mosby, Inc.

LETTERS TO THE EDITOR

Actuarial and Kaplan-Meier survival analysis: There is a difference

David W. Wormuth, MD, MPH

Division of Cardiothoracic Surgery
Strong Memorial Hospital
601Elmwood Ave
Box Surg
Rochester, NY 14642

To the Editor:

While attending the Seventy-ninth Annual Meeting of The American Associationfor Thoracic Surgery in New Orleans, I was dismayed to see the almost universalmisuse of the term "actuarial survival."

There are two general types of analysis for survival information: actuarialand Kaplan-Meier. An actuarial analysis should be performed when the actualdate of a survival event is unknown. The known information is that the eventoccurred between time tn and time tn+1. Actuarial analysis is carried out at specifictime intervals (6 months, 1 year), and the resulting graph will step onlyat those intervals. As the actual failure time is only approximated by theend point, the convention is to attribute a survival time of the fully completedintervals plus half the time of the interval during which the event occurred.Examples of events needing actuarial analysis include population-based deathrates and disease-free survival.

Kaplan-Meier analysis is used when the actual date of the end pointis known. End points not reached are treated as censored at the date of lastfollow-up for the analysis. Kaplan-Meier analysis is undertaken at each survivalevent, death, or censoring, and the graphs will step at each failure timeand may or may not be drawn to show the location of censored observations.Examples of an appropriate event for Kaplan-Meier analysis would be postoperativesurvival when the date of deaths is known.

Most of the misuse of the term "actuarial survival" cameduring presentation of data with well-known end points and graphs that clearlyreflected a Kaplan-Meier analysis. To mislabel the precise survival estimateswith the term "actuarial survival" suggests a limited understandingof survival analysis.

12/8/102480





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