In 2005, Buchanich et al. (1
) reported a potentially serious problem of mortality underascertainment in studies employing a widely used research resource, the Social Security Administration's (SSA) Death Master File (DMF). Mortality ascertainment falls short by 1.7%–4.9% in DMF “exact matches” (those sharing unique identifying information with a subject record). Furthermore, according to Buchanich et al. (1
), an SSA insider estimated that 12%–13% of DMF mortality records are omitted from data provided by half of the US states. In addition, Sesso et al. (2
) estimated that the DMF contains 94.7% of the deaths of males ascertained through the National Death Index (NDI) but only 31.1% of the deaths of females.
Thus, Buchanich et al. (1
) and Sesso et al. (2
) have cast doubt on a strategy of using less expensive DMF searches both to identify deceased subjects and to select subjects for NDI Plus cause-of-death searches. (An NDI Plus search, for an additional fee, returns matches with causes of death, in addition to the date of death returned by a standard NDI search.) In the prospective National Institutes of Health (NIH)-AARP Diet and Health Study (3
), relying on the NDI exclusively to ascertain approximately 2% annual mortality in a cohort of more than half a million subjects would be cost-prohibitive. Assuming a constant 2% mortality rate per year, NDI Plus search costs compound over years 1–5 of follow-up as follows: [(1 – 0.02)year
× 500,000] × 0.21
A key question, therefore, is whether the additional cost of cohort-wide matching to NDI Plus at $0.21 per subject per year—as compared with first restricting submissions to SSA DMF/commercial list update (CLU) matches and paying the National Center for Health Statistics $5 to search the NDI for the cause of death of each supposedly known decedent—would be justified by a potential gain in mortality ascertainment. A related question is how stringency of matching criteria affects the DMF-NDI comparison. With regard to this second question, Hill and Rosenwaike (4
) introduced the method of linkage as an important factor in mortality ascertainment through automated searches of death registries. They argued that the use of stringent criteria for matching on names probably accounts for underascertainment of deaths among females, whose names do not remain reliable identifiers between the college years and death. Such unrealistically stringent matching criteria sacrifice linkage sensitivity for specificity and increase the risk of sex-related bias. In general, the estimated sensitivity of linkage falls in the 75%–95% range, with poorer results being obtained for foreign-born, very young, or pre-1975 decedents (5
In the current study, we compared DMF/CLU matches with NDI Plus results for deaths occurring through 2001 to examine how varying the lower limit of estimated DMF match probability (m scores of 0.60, 0.20, and 0.05) alters the benefits and costs of a subsequent NDI Plus search if the search is limited to likely (though not necessarily exact) DMF matches supplemented by CLU matches. We also examined the benefits and costs of alternative NDI Plus search strategies.