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OCR for page 42
8
Mortality Ascertainment
Do atomic test participants have a reduced life expectancy compared to non-
participants? Are they at increased risk for certain causes of death? Could this be
related to radiation exposure? Our basis for addressing these questions is a com-
parison of death rate, timing, and cause of death for the two cohorts. Correct as-
certainment of mortality data, therefore, is crucial to the validity of this epidemio-
logic study. In this chapter, we first describe ascertainment methods, verification
activities, and validation analyses, and then proceed to an assessment of success.
FACT-OF-DEATH ASCERTAINMENT
As described in Chapter 4, the Department of Veterans Affairs (VA) Bene-
ficiary Identification and Records Locator Subsystem (BIRLS) is the sole source
of fact-of-death ascertainment for this report's dataset. If a person's record was
not found in the BIRLS database, the VA Master Index was searched for addi-
tional descriptive information (e.g., military service number or a middle name)
that might allow a connection to a BIRLS record. BIRLS information, then, re-
sults in a defined set of possible mortality ascertainment outcomes:
· known dead indication of death in the BIRLS database, and
· not known dead no indication of death in the BIRLS database.
Each of these is composed of subgroups described by the availability of other
pieces of information. An individual is classified as known dead if the BIRLS
database (1) explicitly refers to a death, giving a date or a cause, or (2) lists the
location of the VA claims folder as the federal archives. Not known dead is the
accurate way of referring to individuals who in other studies might be classified
42
OCR for page 43
MORTALII YASCERTAINMENT
43
as "alive" or "lost to follow-up." What we do know about these individuals is
that either the BIRLS database (1) has a record of the individual but no reference
to death or federal archives or (2) contains no reference at all to the individual.
The BIRLS procedure identified 38,055 deaths among the 132,949 mem-
bers of the two cohorts. The 1,865 of these deaths that occurred after our defined
end of follow-up (December 31, 1996) were treated as alive for the analyses
presented in this report. Establishing a calendar cutoff of dates of death is neces-
sary to allow time for adequate cause-of-death follow-up activities. The re-
maining 36,190 deaths constitute 27.2 percent ofthe combined cohorts.
Tables 8-1 and 8-2 present the vital status categories for the participant and
referent cohorts.
TABLE 8-1. Vital Status as of December 31, 1996
Participants Referents Total
(n = 68,168) (in = 64,781) (n = 132,949)
%of %of %of
Vital Status No.Cohort No.Cohort No.Cohort
Not Mown dead (no) 49,65172.8 47,10872.7 96,75972.8
Known to be dead (yes) 18,51727.2 17,67327.3 36,19027.2
Total 68,168100.0 64,781100.0 132,949100.0
FACT-OF-DEATH VALIDATION
BIRLS is the only source of fact of death in this study. How complete is
BIRLS as a record of veterans' deaths? If it does not capture almost all deaths,
mortality studies based on these data would be inaccurate. If it captures certain
kinds of deaths or deaths of certain kinds of veterans, inferences based on its
data could be biased. BIRLS was searched for a record of each member of the
combined study cohorts. Not all individuals were found: 23.4 percent of the par-
ticipants and 24.8 percent of the referents were not found in BIRLS.
A veteran might not be found in BIRLS for varied reasons: (1) the record
existed, but MFUA submitted insufficient information, such as a misspelled
name, to identify it; (2) the requesting information was correct, but the BIRLS
record includes a misspelling; (3) a veteran was not entered into BIRLS because
the veteran or a surviving dependent had filed no claim for medical, educational,
loan, death, or other benefits. Similarly, a claims folder identified by BIRLS-
might not be found because (1) the request went to the wrong VA regional office
(VARO), (2) misfiling had occurred, (3) the file was transferred to another
VARO, or (4) the file was transferred to a regional archives center. Finally a
claims folder may be found but not contain the death certificate, the cause of
death, or a legible copy of the certificate. For these reasons, we sought corrobo-
ration of fact of death from other sources.
OCR for page 44
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OCR for page 45
MOR TALITY ASCER TAINMENT
45
Since 1979, the National Death Index (NDI), maintained by the National
Center for Health Statistics, has assembled death certificate-derived mortality data
from each of the 50 U.S. states, New York City, and the District of Columbia, as
well as U.S. territories and protectorates. We first requested information on two
500-member samples of the participant and referent cohorts that had BIRLS rec-
ords both without indication of death and with a BIRLS-noted Social Security
number (SSN). Requiring an SSN allows for an efficient search within NDI and a
check that the person identified in NDI is the same person in the study population.
NDI identified as dead 1.4 percent of the not-known-dead participant cohort
sample and 1.8 percent of the not-known-dead referent cohort sample. These two
rates were not statistically different ~ = .614. Applying these rates to all ofthe not-
known-dead individuals with BIRLS-noted Social Security numbers (21,513 par-
ticipants and 16,917 referents), we estimate that 301 participant cohort deaths and
305 referent cohort deaths were not identified using the BIRLS procedures. These
additions would increase the BIRLS-based study mortality rate from 27.2 to 27.7
percent (participants, from 27.2 to 27.6%; referents, from 27.3 to 27.8%~.
However, we do not have SSNs for a large portion of the study population.
In the two cohorts, of those not-known-dead, approximately 41 percent of the
participants and 63 percent of the referents do not have any SSN in our database.
The participant data that the Defense Threat Reduction Agency provided for this
study from the Nuclear Test Personnel Review (NTPR) Program database in-
clude SSNs for some of the participant cohort who did not have SSNs listed in
the BIRLS database. This NTPR source of information was not available for the
referent cohort. Because using NTPR Social Security numbers would increase
the likelihood of finding only participants in NDI, the study design excluded use
of NTPR Social Security numbers because they would have allowed non-
equivalent mortality ascertainment procedures for the two cohorts, introducing a
bias into the ascertainment of the outcome data. However, the availability of
NTPR Social Security numbers for participants did allow us to estimate how
many deaths might have been ascertained if we had more complete SSN cover-
age. Thus, we submitted two additional 500-member samples of not-known-
dead participants with NTPR SSNs to NDI. One group was in the BIRLS data-
base without a BIRLS-noted SSN and one group was not in the BIRLS database
at all. Because both BIRLS identification and SSN availability are associated
with both vital status and the ascertainment of vital status, we wanted to use
these samples to estimate the size of any differential in mortality rates that might
stem from differences in information ascertainment rather than an effect of par-
ticipation. Although these estimates were not used to adjust the analysis, they
are useful in discussing the extent to which deaths have been missed and imbal-
anced ascertainment could influence study findings.
NDI identified as dead 4.6 percent of the not-known-dead participant cohort
sample that was found in BIRLS without a BIRLS-noted SSN and 5.6 percent of
the not-known-dead participant cohort sample that was not found in the BIRLS
database at all.
OCR for page 46
46
THE FIVE SERIES STUDY
Although ascertainment was not complete, these estimates provide a not-so-
alarming approximation of the underascertainment of deaths in this study. There
are 3,957 participants in the first group and 2,896 in the second. Applying the 4.6
and 5.6 percent sample estimates to the full groups would yield 182 deaths in the
first group and 162 in the second. Applying these same rates to the participants
without NTPR (or BIRLS) SSNs, we estimate an additional 411 deaths among the
participants in BIRLS with neither BIRLS nor NTPR SSNs and 593 deaths among
the participants with no record in BIRLS and no NTPR SSNs. Adding all of these
groups together, we estimate that BIRLS did not identify 1,649 deaths. Therefore,
the estimated BIRLS ascertainment rate for participants is 91.8 percent.
For the referent cohort, which does not have NTPR SSNs at all, we must
use participant data to produce ascertainment estimates. Applying the 4.6 per-
cent additional death ascertainment to referents in BIRLS but without a SSN
yields 609 deaths; 5.6 percent additional deaths among referents not in BIRLS at
all amounts to 900 deaths. Taken together, an estimated 1,814 referent cohort
deaths were not ascertained by the BIRLS procedure, yielding an ascertainment
of 90.7 percent of the deaths in the referent cohort.
Relatively few formal studies have been undertaken to determine the com-
pleteness of veteran death reporting via the BIRLS system, most of them involving
either World War II or Vietnam era veterans. Studies of deaths among World War
II veterans (Page, 1992; Page et al., 1995) estimated, respectively, that 92 and 95
percent of veteran deaths could be found in BIRLS. Studies of deaths among Viet-
nam era veterans (Page, 1993; Page et al., 1996) generally showed slightly lower
percentages of BIRLS completeness, 90 percent, except that Boyle and Decoufle
(1990) found BIRLS to be only 80 percent complete. A study by Fisher et al.
(1995) of a group of hospitalized, largely pre-Vietnam-era veterans showed that
BIRLS was 96 percent complete for death ascertainment. Although the methods
employed across these studies are varied, all except the Boyle and Decoufle study
showed the completeness of veteran death reporting in BIRLS to be 90 95 per-
cent. Although the veterans studied here are, for the most part, neither World War
II nor Vietnam era vets, we believe that the completeness of death reporting in
BIRLS is roughly the same among the veterans in the present study.
DATE OF DEATH
BIRLS was the principal source of death date for the study analyses (see Ta-
ble 8-3~. An actual date was noted for 97.2 percent of the known dead individuals.
No date of death was identified for less than 0.1 percent of the known deaths. An-
other 2.1 percent of the death dates were obtained from the VA Master Index, the
death certificate, or NDI. For most of the remaining deaths, we were able to cal-
culate an approximate date of death based on the date a record was transferred
from a VA regional office to a federal archives center. This estimate is possible
because VA sends to the archives only those VA benefit claims records that are
inactive due to the death of veteran and any surviving beneficiaries.
OCR for page 47
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OCR for page 48
48
THE FIVE SERIES STUDY
We used the records with both a BIRLS-noted date of death and a date of
folder transfer to archives to calculate the lag time between death and record
transfer. Because the efficiency of both the VA and the National Archives and
Records Administration (NARA) may have varied over the years, we calculated
these lags by year. These lags, generalized to multiyear periods as appropriate,
were then applied to the 204 records that had only the record transfer date to
impute a date of death.
CAUSE-OF-DEATH ACQUISITION
The two sources of cause-of-death information are both death certificate
based: the death certificate itself and electronic tapes compiled from the death
certificates. The BIRLS database provides the location of the claims folder: a
specific VA regional office (VARO) or a specific federal archives center
(FARC). Following established VA and NARA procedures, we requested that
the VARO and archives staff pull the folder and send us a copy of the death cer-
tificate for each death. Our contract nosologist supplied codes for all causes of
death listed and selected one as the underlying cause and the others, if any, as
associated causes.
In cases in which the VAROs and FARCs could not produce a death certifi-
cate and for which we had date of death, we requested death certificate informa-
tion from NDI-Plus if the death occurred in 1979 or later. NDI-Plus returned an
electronic tape with identifying information and underlying and associated
causes of death.
Tables 8-4 and 8-5 are limited to those members of the study population
who are known to have died (excluding those who died after December 31,
1996~. Of these 36,190 individuals, a cause of death is not available for 5.9 per-
cent. The difference between the participant cohort's 4.5 percent and the referent
cohort's 7.3 percent is statistically significant. For the causes of death that we
did obtain, 65.5 percent came from the death certificate and 34.5 percent from
the National Death Index-Plus.
CAUSE-OF-DEATH VALIDATION
To determine the level of agreement between the two sources of cause-of-
death codes, we processed a sample of 200 records through both ascertainment
paths. Neither source- the contract nosologist or the NDI-Plus database was
considered the standard; discrepancies were counted, not correct and incorrect
codes. Eleven of the underlying cause-of-death codes were sufficiently different
so that the death would be assigned to a different cause-specific analysis group.
(Another 10 had differences [e.g., in the fourth digit of the International Classi-
fication of Diseases code] that exceeded the level of detail examined in this re-
port.) For 4 of the 11, the two sources had the same codes but specified different
ones as the underlying cause of death.
OCR for page 49
MOR TALI TY A SCER TAINMENT
TABLE 8-4. Cause-of-Death Availability Deaths Only
49
Participants with
Death Indicated
Referents with
Death Indicated
Total with
Death Indicated
AvailabilityNo. % No. % No. %
Available17,675 95.5 16,378 92.7 34,053 94.1
Missing842 4.5 1,295 7.3 2,137 5.9
Total18,517 100.0 17,673 100.0 36,190 100.0
TABLE 8-5. Cause-of-Death Source Deaths Only
Participants with
Death Indicated
Referents with
Death Indicated
Total with
Death Indicated
Source No. % No. % No. %
Death certificate 11,893 67.3 10,422 63.6 22,315
NDI-Plus 5,782 32.7 5,956
Total
18,517 100.0
36.4 11,738
16,378 100.0 34,053
65.5
34.5
100.0
NOTE: NDI = National Death Index.
We looked at the records that had a malignant neoplasm in any of the cause
fields from either source to determine whether cancers the prime endpoint of
this study-were noted similarly by the two coding sources. There were 74 rec-
ords with malignancy codes; of these, 6 were discrepant in the underlying cause-
of-death field. Five of these involved the selection of the underlying cause from
among all listed causes. Of the six discrepancies, three do not affect the analysis
of the broad category of all-malignancy deaths but, because they select a differ-
ent site-specific cancer, would affect that level of analysis.
Representative terms from entire chapter:
death certificate
