1 Department of Preventive Medicine and Community Health, Division of Sociomedical Sciences, University of Texas Medical Branch, Galveston, TX 77555-0460
2 Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555-0460
3 Department of Internal Medicine, Division of Geriatrics, University of Texas Medical Branch, Galveston, TX 77555-0460
4 Department of Preventive Medicine and Community Health, Division of Epidemiology and Biostatistics, University of Texas Medical Branch, Galveston, TX 77555-0460
In a paper appearing several months ago in the Journal (1), we compared mortality ascertainment carried out using the National Death Index (NDI) with mortality ascertainment conducted through fieldwork for the Hispanic segment of the Established Populations for Epidemiologic Studies of the Elderly (H-EPESE). The H-EPESE follows a cohort of older Mexican Americans residing in five southwestern US states who were selected in 19931994. Because, in the H-EPESE fieldwork, the informant used when a subject could not be located was usually a relative of the subject, we considered the collected information to be correct, and we compared it with information from the NDI under a scoring algorithm similar to that used to match National Health Interview Survey (NHIS) data with NDI data. We calculated 21 percent underascertainment for the NDI and 9 percent overascertainment, for a net underascertainment of 12 percent (table 1).
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Unfortunately, a postpublication review identified processing errors that had led us to overstate both underascertainment and overascertainment. Some of these errors were discovered by colleagues in the Social Security Administrations Office of the Chief Actuary, while others we found ourselves in an internal review.
Approximately one third of the 177 proxy-reported deceased cases that failed to match using the algorithm score did so because of errors in the preparation of the submission records. In a majority of these cases, the NDI nonetheless identified a death record that scored close to the threshold for acceptance. In other cases, incorrect Social Security numbers were supplied to the interviewers by the interview subjects. It remains a matter of speculation as to what degree such a pattern would be generalizable to other studies. We are preparing to send a corrected submission to the NDI. We expect to find that the true underascertainment error will be one half or less the magnitude originally reported.
Overascertainment should have been reported as 28 subjects rather than 76 subjects interviewed after the cutoff point for the vital status comparison; this was misstated because of a programming error. In none of the 28 cases was a Social Security number match achieved. Manual review of death certificates would probably have led to the rejection of most of the false matches.
On a positive note, our analysis (1), as well as recently published studies (2, 3) and unpublished evaluations done in conjunction with the recent release of expanded versions of the National Longitudinal Mortality Study data and the NHIS-NDI linked file, has spawned greater determination in the research community to authoritatively address the question, To what extent are ascertainment bias and other data quality issues contributing to the Hispanic mortality advantage? A work group is being formed, and studies using the NHIS-NDI, National Longitudinal Mortality Study, and Social Security data are being planned.
Acknowledgments
The authors thank Bert Kestenbaum and B. Reneé Ferguson of the Office of the Chief Actuary, Social Security Administration, for identifying some of the above errors. The authors are also grateful to Christine Cox and Donna Miller of the National Center for Health Statistics for information supplied during this review.
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