Journalof Epidemiology

A Method

Vol . 10, No. 6 Novfor Identifying

Underlying

Causesof Death

Tamiko Iwasaki 1, Toshio Miyake 1, Sumio Ohshimaand Takesumi

Yoshimurain EpidemiologicalStudy

1, Shin' ichi Kudo 1,2

To obtain the underlying causes of death in individuals of a cohort (male only), the items of dateof birth, date of death and address code at the time of death were linked between the data ofresident cards and the death tapes of National Vital Statistics supplied by the Ministry of Healthand Welfare. As a result, the persons who have the same information for above mentioned threeitems between the resident cards and the death tapes accounted
for 97.4%. If the persons whohad the same information for three items except one item were considered
to be identical, theyaccounted
for 99.4%. It would be concluded
that underlying cause of death can be obtained byrecord linkage of death tapes of National Vital Statistics
with three informations
in residencecards, dates of birth, dates of death and address codes at the time of death, even without namesof the individual in the death tapes. The matched rate would be high enough for epidemiologicalstudies.
J Epidemiol, 2000 ; 10 : 362-365
underlying

causesof death,record linkage, National Vital Statistics,

INTRODUCTION

resident

cards

males, only the death tapes of males were obtained and used.
The method for identifying underlying
causes of death bymean of record linkage of resident cards and the death tapes
was performed.
This paper reports the results of record linkage of the death
information from the resident cards and the death tapes sup-Since 1990, the Institute of Radiation Epidemiology of theRadiation Effects Association has been studying the relationship between exposure to radiation and causes of death in people who were engaged in radiation work at nuclear facilities.
The study was entrusted to the Institute by the Science andTechnology Agency to study the health effects of exposure to
low-dose and low-dose rate radiation on human 1). As a study
method, the copies of resident cards of the subjects underinvestigation were obtained to confirm whether they were alive
or dead. For the persons who were dead, their underlying
causes of death were identified by record linkage with thedeath tapes of National Vital Statistics (hereinafter referred toas "death tapes") supplied by the Ministry of Health andWelfare (M.H.W.) of Japan. In these death tapes, however,there were no descriptions of the names of the deceased.
Therefore, three items of date of birth, date of death andaddress at the time of death were used for identification of individuals. Since the subjects under investigation were limited toplied by the M.H.W., discusses the problems of this method,and proposes this method as a useful procedure for epidemiological studies in Japan.
METHODThe copies of the resident cards of the deceased contain thenames, dates of birth, addresses at the time of death, and datesof death of the deceased, without information of the causes ofdeath. To obtain the underlying causes of death, therefore, thedeath information in resident cards of the deceased were linked
with the death tapes supplied by the M.H.W. For using thedeath tapes from the M.H.W., the approval of the Director
General of the Managementand Coordination
Agency wasReceived October 29, 1999 ; accepted May 15, 2000.
1 Institute of Radiation Epidemiology, Radiation Effects Association.
2 Dept . of Clinical Epidemiology, Inst. of Industrial Ecological Sciences, Univ. of Occupational and Environmental Health, Japan.
Address for correspondence : Tamiko Iwasaki, Institute of Radiation Epidemiology, Radiation Effects Association, 1-9-16, Kajicho,
Chiyoda-ku, Tokyo, 101-0044 Japan.

362

363

T. Iwasaki,

obtained in accordance with the Notification No. 10 dated
February 9, 1994 of the Agency under the Law of Statistics.
The death tapes contain the information about dates of birth,dates of death, address codes at the time of death. In the present paper, it was adopted underlying causes of death coded by
the ICD 9 (140-239) for about 3,200,000 of all the maledeaths aged 18 or older from 1986 to 1992. Among radiation
workers investigated, 1,758 deceased cases were confirmed byresident cards during the same periods. The identification
work was performed by record linkage of 3 items of the datesof birth, dates of death and address codes at the time of death
between the information of resident cards and that of the deathtapes.
Identification method
1. The deceased who have the same information about thefollowing three items as that of resident cards wereretrieved from the death tapes:(1) Date of birth (seven figures including the name of anera)(2) Date of death (seven figures including the name of anera)(3) Address code at the time of death (five figures in eachcode assigned by the Ministry of Home Affairs)
The deceased who had the same information about theabove three items in the resident cards and magnetic tapes
were regarded as identical.
2. The deceased who did not have the same information
about these three items were subjected to record linkage
again as follows:(1) The persons who have the same information about thedate of death and address code at the time of death,except the date of birth.
(2) The persons who have the same information about thedate of birth and address code at the time of death,except the date of death.
(3) The persons who have the same information about thedate of birth and date of death, except the address codeat the time of death.
All the cases which did not completely match with eachother in any of the above three items were retrieved as "a similar list." Among these retrieved cases, the persons who cameunder the following conditions were considered to be identical:
For example, in (1) above, the persons with their dates ofdeath and address codes at the time of death matching witheach other were retrieved, and then the persons with their datesof birth most similar to each other (e.g., February 11 andFebruary 17) were considered to be identical as shown in
Table 1. In (2) above, the persons with their dates of birth andaddress codes at the time of death matching with each other
retrieved likewise, and then the persons with their dates ofdeath most similar to each other (e.g., March 10 and March 9)

et al.

were considered to be identical as shown in Table 2. In (3)above, the persons with their dates of birth and dates of deathmatching with each other and only the address codes being different were retrieved likewise. Among those retrieved persons,those with the identical dates of birth and dates of death in theaddress codes of neighboring towns and villages (e.g., 14101and 14102) were considered to be identical. In this record linkage, a COBOL program was used.
RESULTS
The persons whose dates of birth, dates of death and address
codes at the time of death completely matched with each otherwere 1,713 (97.4%) of the 1,758 surveyed (Table 3). The per-Table

1. Cases identified

by changing

of date of birth.

* 1935: Showa 10, 1921: Taisho 10 (in the name of an era)Table

2. Cases identified* 00: Unspecified

by chaneineof date of death .

Identificationof Underlying

sons who had the same information about these three items
were judged to be identical and given their underlying causesof death. For 45 persons who did not have the same information about these three items, the persons who have the same
information for two of the three items as that in the resident
cards were retrieved from the death tapes. Then, record linkage was tried again for the persons who have the same information for two of the three items, in the same way as for theidentification method.
As shown in Table 3, the persons whose dates of death andaddress codes at the time of death matched with each otherwere 14 (0.8%), the persons whose dates of birth and address
codes at the time of death matched with each other were 16(0.9%), and the persons whose dates of birth and dates of deathmatched with each other were 5 (0.3%). These persons could
be judged to be identical. On the other hand, the persons who
were completely different from each other in this record linkage and could not be identified were 10 (0.6%). In otherwords, the underlying causes of death of 1,748 (99.4%) out of
the 1,758 deaths were finally obtained by this method.
There was no duplication of deaths in this record linkage
method.
DISCUSSIONEpidemiological studies have been carried out with people
engaged in radiation work in order to know the effects of exposure to low-dose and low-dose rate radiation on the causes of
their death, including cancers 1). The resident cards of subjectsof investigation were obtained to confirm whether they werealive or dead. However, these resident cards did not contain

Causesof Death364

the causesof death.

To knowwasin which

the underlyingusedfirmedby record

dent cards
Theof the records

It is also

examination

cancer,linkageof thesebut theretapes

usingin this study.

birth,

dates

of deathon theconsidered

methodcodes

completely

therecords

the personsof the deathmationfor abovecards

and the deathtapes

accounted

Table

3, the results

showthat the percentage

threeof birth,dates

of death

timematchingwitheachof death

The same

identifyingof circulatory
matchedmethoddisordersrate wasobtained

97.4%

thiscards

withthe same

infor-

the resident

for 97.4%.

As seencodes

is as highHe alsoat theas 97.4%.

in the follow-up

as sameinof the deceased

and address

was usedtapes

betweenotherby Ueshima4).

ofthoseAs a result,

who haveitemswith the dates

withon the death

thosementioneddates

of deathto be identical,

in resident

study

reportedthat

as in the presentresults.
Whenthreepersons

items

who have the same

are included,

information

the rate of concordance

Table 3. Results of record linkage for underlying causes of death (Subjects: 1,758).

* See text .

matchedconsideredarein the death

whoseof the deceased.

death

tapes

the namesat the timeof death recorded

to be thoseof linkage

in old data throughthe persons

were,ofregistrationof the names

tapes2.3). That

due to cancers

records,

cards

reg-of cancer

studiesshown

In theseThen,causesin cancer

precision

the regional

persons

and address

death

and the underlying

theis no description

in the resident

recordedis performed

from

data.

of the resi-by the M.H.W.

of the deceased

collectedmentioned,shown

suppliedepidemiologicalto be the identical

recordwerelinkageconfirmationin new data

the information
tapes

in measuring

and in various

is, this enables
shown

usedof death , a methodof death were con-causes

betweenand that of the death

methodistry.

linkagethe causes

for two of thebecomes

as

365

T. Iwasaki, et al.

high as 99.4%. It is considered that the reason for such a highcorrespondence rate is due to our study using the death recordin resident cards and magnetic tapes, which are both the official records.
As a method similar to the above, the records of birth registration from National Vital Statistics are linked with those ofdeath registry of children aged one or less after birth 5). In thiscase, the records of birth registration from the National Vital
Statistics were manually linked with those of death registry ofchildren aged one or less after birth in the 1989's birth cohortof 409,679 in 18 prefectures, and it was possible to identify thedead at 96% (1,840/1,909) from the record linkage of the birth
registration and the death registry.
Among Japanese males who died between 1986 and 1992
(4,581,654) the probability of persons whose dates of birth,dates of death and address codes at the time of death matchwith those of different persons by chance (2,839) are as low as
6/10,000 as a result of a study. The persons who have thesame information for these three items, therefore, are probablyidentical.
This, however, only means the match of linkage between
two records. It is impossible to confirm that they are definitely identical. Ohtaki et al. 6) have done a theoretical analysis ofrecord linkage for related documents of atomic bomb survivors.
According to their report, for example, the probability
that in a paired sample of different persons the family nameand present address of a person match with those of the counterpart is 0.52 X 10-5, and the probability that in a paired sample
of different persons the family name and present address of aperson do not match with those of the counterpart is 0.997. As
shown in the above, the probability that the matched data of
two persons are identical and they are actually different persons is very low. Therefore, we think this method shows highperformance in record linkage.
As a measure for verifying the identification of the deceasedin this record linkage method, it will be necessary to confirm
that the deceased is truely identical by perusing the death regis-tration form (kept only five years) at public health centers ordeath certificates kept at the Legal Affairs Bureaus, Ministry ofJustice.
ACKNOWLEDGEMENT
The authors are grateful to Dr. Toshiyuki Kumatori and Mr.
Masato Kaneko for their great effort and advice .
REFERENCES
1. EpidemiologicalStudy Group of Nuclear Workers(Japan), First analysis of mortality of nuclear industry
workers in Japan, 1986-1992. J. Health Physics, 32, 173184(1997).
2. Fujimoto I, Hanai A, Tsukuma H, Hiyama T. Role of
population-based cancer registry in cancer epidemiologyEpidemiological studies in the cancer registration inscheme in Osake, Japan-. Jpn. J. Hyg., 1994; 49: 543558. (in Japanese with Summary in English)
3. Okamoto N. Natsui S., from Report on The ResearchGroup for Population- based Cancer Registries in Japan,
1993. (in Japanese)
4. Ueshima H. Follow-up study of 1980 national survey ofcirculatory disorders (NIPPON DATA). J. Japan.
Assoc.Cerebro-Cardiovascular Disease Control (JACD),
1997; 31:231-237. (in Japanese)
5. Fujita T, Minowa M, Miura Y, Kamiya K. Risk factors
for neonatal and postneonatal mortality - A record-linkage study based on vital statistics-.Nippon Koshu EiseiZasshi, 1994; 41: 34-45. (in Japanese with Summary inEnglish)
6. Ohtaki M, Munaka M, Kurihara M , Hayakawa N,Yamamoto H, Ueoka H, Sumida H, Hiraoka M . A mathematical theory of collation for record linkage among thedata related to A-bomb survivors. J .Hiroshima Med.
Ass., 1982; 35: 356-358. (in Japanese)