1 Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
2 Merck & Company, Inc., Whitehouse Station, NJ
Reprint requests to Jeanine M. Buchanich, Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, A446 Crabtree Hall, 130 DeSoto Street, Pittsburgh, PA 15261 (e-mail: jeanine{at}pitt.edu).
Received for publication November 19, 2004. Accepted for publication March 21, 2005.
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ABSTRACT |
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cause of death; cohort studies; contact tracing; records; social security
Complete and accurate vital status ascertainmentdetermining whether a subject is living or deceasedis of great importance in cohort studies. Two of us (J. M. B., G. M. M.) coauthored papers evaluating different methodologies for tracing vital status in mortality studies of large cohorts that recommended a two-stage protocol (1, 2
). The first stage involved using the Pension Benefit Information Company (PBI; Tiburon, California) to identify deaths among cohort members not known to be alive or deceased. This company uses information from the Social Security Administration (SSA), its own sources, and direct information from several US states and the Railroad Retirement Board to maintain a database of deaths. The second stage involved sending information on all cohort members known to be deceased according to PBI to the National Death Index (NDI) for a coded cause of death. Using the two-stage protocol eliminated a great deal of the cost associated with sending data on all cohort members not known to be alive or deceased through the NDI. We confirmed the accuracy of this two-stage vital status protocol by conducting extensive tracing of subjects assumed to be alive. Our results indicated that the published methodology was sound and that approximately only 0.5 percent of subjects' vital status was misclassified (1
).
Recently, during the vital status ascertainment phase of an ongoing occupational mortality study, we discovered a potentially serious problem with stage I of our tracing protocolthe use of PBI's tracing serviceor any tracing that relies on SSA Death Master File records to identify deaths. In a cohort of 14,260 workers, 921 deaths were confirmed through PBI, but an additional 47 deaths (4.9 percent) known to the company sponsoring the research were not identified. Our investigation, which began with an inquiry to PBI, revealed that a number of states restrict the information included in the SSA's Death Master File that is available to researchers and the public as a source of death information. According to the SSA, 25 states report deaths to the SSA for fraud and abuse purposes only, and those states' deaths do not appear in the Death Master File if they are not already included in existing SSA databases (P. McFadden, Social Security Administration, personal communication, November 12, 2004). The SSA is not allowed to report which states do or do not restrict death information to the SSA Death Master File.
We next contacted the NDI program of the US National Center for Health Statistics to confirm their death identification protocol. The Center verified that it has independent agreements with each state health department, which collects and reports all state deaths directly to the NDI. On the basis of this information, we formulated a revised two-stage tracing protocol, one that uses both the SSA and the NDI.
To validate our revised vital status tracing protocol, we sent to NDI information on the cohort members assumed to be alive. We used our previously published protocol (1, 2
) from two occupational cohorts: 6,824 subjects from the original occupational cohort study and 3,597 from a second occupational cohort study. In the original study, NDI identified 19 (2.0 percent) additional deaths not found by PBI or included in the SSA Death Master File (note: 22 of the 47 deaths known to the company were international deaths not captured by NDI); in the second study, NDI identified 43 (1.7 percent) additional deaths not found by PBI or included in the SSA Death Master File, including two with the outcome of interest to the study.
As a result of these findings, we recommend a revised two-stage vital status tracing protocol that will maintain high death ascertainment rates while minimizing tracing costs. For stage I, we recommend sending to the SSA data on all subjects for whom vital status is unconfirmed. With the enactment of section 311 of the Social Security Independence and Program Improvements Act of 1994, the SSA is once again able to confirm living, unknown, and deceased vital status at a cost of $0.1925 per person searched for the first 25,000 records and $0.0355 thereafter. On the basis of a sample of several SSA computer matches, the SSA estimates that 1213 percent of the cohort records will be assigned an unknown vital status (P. McFadden, Social Security Administration, personal communication, November 12, 2004). Cohort records assigned an unknown vital status include both those that contained insufficient (or inaccurate) information to qualify for a match and those matched with death records received by SSA from the 25 states that restrict access to some information. For stage II, we recommend sending to the NDI information on all subjects to whom SSA assigned an unknown vital status as well as all subjects whom SSA identified as known decedents. Doing so will allow for accurate vital status tracing of the unknown subjects and eliminate unnecessary NDI costs associated with searching for subjects who could be confirmed alive according to the SSA. The NDI search will also identify coded cause and date of death for decedents. The NDI charges $0.21 per person per year searched for subjects whose vital status is unknown and $5.00 per person for coded cause of death for known decedents.
Compared with the NDI-only trace, the revised two-stage tracing protocol will add some additional time (approximately 4 weeks). However, this protocol will result in a significant cost savings (even after factoring in a modest increase in programming costs). For stage I of the revised two-stage protocol, the turnaround time for a file is approximately 3 weeks once approval from the SSA is granted. The programming time associated with file preparation and analysis is approximately 1 day: 2 hours to prepare the file and 6 hours to review the results and add the new information from SSA to the cohort-tracing database. This level of effort, turnaround time, and cost is nearly identical to that for stage I from our original two-stage tracing protocol.
For a hypothetical cohort of 5,000 subjects, we estimated the cost breakdown for using this new vital status tracing protocol as follows:
In comparison, the total cost associated with initially tracing all subjects through the NDI would be as follows: 5,000 subjects x $0.21 x 12 years = $12,600.00.
In this hypothetical example, using the revised two-stage tracing protocol versus only the NDI results in almost a 40 percent cost savings. The actual savings associated with using the revised two-stage protocol will be a function of several cohort-specific variables, including the age distribution of the cohort, number of years to trace, and states of residence for cohort members.
This revised two-stage tracing protocol provides researchers with higher death ascertainment rates, resulting in increased validity. It also allows researchers to confirm living cohort members, whose vital status could only be assumed using the original tracing methodology. This new protocol will enable researchers to maximize vital status ascertainment while containing costs associated with death identification. We are currently preparing a more detailed description of the underascertainment, which will include the results of contacting the state health departments directly to determine the extent to which they restrict death information reporting to the SSA Death Master File, when this restriction occurred, and whether any change in reporting status is anticipated.
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ACKNOWLEDGMENTS |
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