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American Journal of Epidemiology Vol. 140, No. 5: 487
Copyright © 1994 by The Johns Hopkins University School of Hygiene and Public Health

correction

ERRATUM

ABSTRACT

Beth Alderman and coworkers discovered an error in the analysis for the article entitled, "Cautions in the Use of Antecedents as Surrogates for Confounders" (1). Because they did not fully understand the way in which SAS stores data, they overestimated the frequency of inequalities based on variables calculated in SAS. For example, they found on reviewing their data that 7.0000 might variously be considered as less than, equal to, or greater than 7. They have since found a note in the SAS documentation (2) that explains this phenom enon, namely, that 0.3 * 100 is stored not as 30 but as a number very close to 302. Reanalysis of their scenarios based on rounded variables changed their results but did not substantially affect their overall findings and conclusions. For example, antecedent adjustment led to partial adjustment for the effects of the confounder in 35 percent rather than 41 percent of scenarios, to full adjustment in 5 percent rather than 3 percent, to overadjustment of 4 percent rather than 9 percent, and to counteradjustment in 40 percent rather than 45 percent. The revised data are available upon request.

The Journal regrets any inconvenience this may have caused.


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