a Statistics Sweden.
b Department of Public Health and Caring Sciences, Unit of Social Medicine, Uppsala University, Sweden.
Reprint requests to: Lars Age Johansson, BV/HS, Statistics Sweden, Box 24 300, SE-104 51 Stockholm, Sweden.
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Abstract |
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Methods Swedish death certificates for 1995 were linked to the national hospital discharge register. The resulting database comprised 69 818 individuals (75% of all deaths), 39 872 (43%) of whom died in hospital. The diagnostic statements were compared at Basic Tabulation List level.
Results The last main diagnosis and the underlying cause of death agreed in 46% of cases. Agreement decreased rapidly after discharge. For hospital deaths, the main diagnosis was reported on 83% of the certificates, but only on 46% of certificates for non-hospital deaths. Malignant neoplasms and other dramatic conditions showed the best agreement and were often reported as underlying causes. Conditions that might follow from some other disease were often reported as contributory causes, while symptomatic and some chronic conditions were often omitted. In 13% of cases, an ill-defined main condition was replaced by a more specific cause of death.
Conclusions There is no apparent reason to question the death certificate if the main diagnosis and underlying cause agree, or if the main diagnosis is a probable complication of the stated underlying cause. However, cases in which the main diagnosis cannot be considered a complication of the reported underlying cause should be investigated, and assessments made of the feasibility and cost-effectiveness of routinely linking hospital records to death certificates.
Keywords Cause of death, death certificates, main diagnosis, hospital records, quality control, medical record linkage
Accepted 27 October 1999
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Introduction |
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A number of quality problems have been identified, ranging from diagnostic difficulties to national bias in data processing.211 Inaccuracy in death certification is a main concern,2 and producers of official mortality statistics often take great pains to monitor and correct death certificates, for example by means of manual and computerized verification. Traditional editing techniques are heavily biased, however, since they will only capture evident errors. Completed forms that look correct, but do not correspond to the actual facts of the casea serious problem in any assembling of statistical datawill not be discovered.12,13
Occasionally, clusters or random samples of death certificates have been compared to their corresponding medical records.14,15 While this approach avoids the bias inherent in traditional editing, the method is unfortunately far too slow and expensive for routine use. The result is also an assessment of data quality rather than an improvement in routinely produced statistics.
In many countries decedents have records in other computerized registers. Several studies have used register linkage to assess the quality of cause-of-death data, or to arrive at better estimates.10,1621 Goldacre linked cause-of-death data for the Oxford region to hospital discharge records, and showed that mortality statistics do not necessarily reflect the actual disease pattern among people who die.22 It has been suggested that similar data linkage could also be used to improve the quality of mortality statistics.16 In this study we match hospital discharge data to death certificates at the national level and discuss the implications of our findings for the routine production of mortality statistics.
The definitions of hospital discharge main diagnosis and underlying cause of death do not coincide. The main diagnosis, as defined in ICD-9, is the main condition treated or investigated during the relevant episode. The underlying cause of death, on the other hand, is (a) the disease or injury which initiated the train of morbid events leading directly to death, or (b) the circumstances of the accident or violence which produced the fatal injury.1 For the purpose of this study, we thus assumed that different definitions might account for many discrepancies between main diagnosis and underlying cause of death. But we also assumed that some discrepancies might still be hard to explain, and might deserve further analysis.
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Material and Methods |
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The Swedish Hospital Discharge Register is a compilation of each individual hospital's discharge records, performed first at regional level by the 26 health administrative authorities, who forward them to the National Board of Health and Welfare. According to the Board's estimates, about 99% of all public hospitalizations are included.23 Thus, the vast majority of inpatient deaths are covered, since Sweden has very few providers of private inpatient care.24 Discharges from nursing homes are not reported. While the Board of Health performs extensive checks on the data received, coding and data entry are performed locally at each hospital. The diagnoses are generally coded by the physician responsible for the discharge. In 1995, Swedish hospitals used the KS87, an adaptation of ICD-9.25 The Hospital Discharge Register has one record for each episode of hospital care, each record containing a unique patient identifier, particulars of the hospital department and the hospitalization, as well as a main diagnosis, a maximum of five contributing conditions, the external cause in cases of injury, and codes for any surgery performed.
Matching the personal identification numbers, we extracted data on all hospital discharges within one year prior to death. The resulting database comprised 224 794 hospital discharges (69 818 individuals), corresponding to almost 75% of all deaths. Of these, 39 872 people (43% of all deaths) died in hospital.
At detail level, the Swedish KS87 classification does not always coincide with the international English version of the ICD. The discrepancies, which are most apparent in the E series (external causes), would have caused spurious differences at both four- and three-character level. To avoid this, we decided to translate all condition codes in both registers into categories of the ICD-9 Basic Tabulation List (BTL). The three-digit BTL is a cause-of-death shortlist of about 230 categories. It corresponds fairly well to the level of detail at which mortality statistics are generally analysed. Practical tests on compatible parts of the two classifications also indicated that BTL groups would not yield a dramatically different result from three-character ICD categories (data not shown). The BTL groups do not, however, cover all causes of death and can thus not be used for calculation of totals. For this reason, we used Statistics Sweden's extended version of the BTL, in which residual groups have been added throughout the list.26
We then compared the hospital discharge data with the conditions mentioned on the death certificate, concentrating on the main diagnosis of the last hospital discharge and the underlying cause of death.
To assess the general correlation between main diagnosis and underlying cause of death, we analysed how the correlation varied with sex, age, time elapsed from hospital discharge to death, main diagnosis, and the number of different conditions in the last hospital discharge record. We scanned the death certificates for any mention of the main diagnosis as either underlying or contributory cause. Since we believed that later developments might make hospital discharge data less useful if the patient had died some time after discharge, we decided to limit the remaining analyses to hospital deaths. For those, we examined the death certificate to see if it contained more specific diagnostic information than the hospital discharge record. We also tabulated the underlying cause for deaths in which the underlying cause did not match the main diagnosis, and checked if the agreement between main diagnosis and underlying cause varied with the autopsy rate.
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Results |
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Discussion |
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We found the best correlation for the malignant neoplasms (Table 2), and it is not hard too see why. A malignant neoplasm, reported as the last main diagnosis, is obviously very likely to be the underlying cause of death. It also seems reasonable that a greater number of reported conditions in the discharge record correspond to a lower degree of correlation with the underlying cause (Figure 2
). The more conditions present, the more the physician has to choose from when filling in the death certificate.
Like Goldacre,22 we distinguished three broad groups of main diagnoses when analysing hospital deaths; those likely to be reported as the underlying cause of death (Table 3a), those likely to be reported as a contributory cause of death (Table 3b
), and those likely not to be mentioned on the death certificate (Table 3c
). As to improving the quality of the death certificates, the first group is probably of least significance. The fact that the main diagnosis and the underlying cause agree does obviously not guarantee that the death certificate is correct. However, the likelihood of obtaining a more probable cause of death from consulting the hospital records seems small. For an example from our data see Table 6
, relationship a.
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In other cases, however, the main diagnosis is not a probable complication of the stated underlying cause (Table 6, d). That does not, of course, necessarily imply that the certificate is wrong. The certifying physician may have had access to information that is not present in the hospital records, and the later of the two records could simply reflect a more considered opinion than the first. One should also allow for competing causes of deathif the patient suffered from several serious conditions, the physician may have had good reason to select one of them for the discharge register, and another for the death certificate. In addition, the hospital discharge register is in no way exempt from errors. In a Swedish study in which reported hospital discharge diagnoses were checked against medical records, the error rate was estimated to be 14% at the ICD four-digit level.28
Nevertheless, incompatible morbidity and mortality statements might indicate that something is wrong. Goldacre22 found that the underlying causes actually reported in non-concordant cases tend to be circulatory or respiratory conditions: ischaemic heart disease, acute myocardial infarction, heart failure, acute cerebrovascular disease and pneumonia. None of these conditions would arouse the curiosity of a statistical office, at least not when stated as cause of death for elderly people. By comparing death certificates with their corresponding hospital records, however, we might find an incompatibility that indicates a potential quality problem that should be investigated.
Obviously, a statistical edit based on the relationship between main diagnosis and underlying cause would not solve all quality problems. Non-hospital deaths, for example, require a different approach. Linkage will not help either if the main diagnosis and underlying cause are identical but both incorrect. Moreover, the cost and time required for the procedure might prove prohibitive, or the quality gains insignificant in relation to the effort.
Thus, a cost-benefit analysis is needed, including an analysis of which errors a method based on record linkage is likely to identify and which it is likely to miss. To that end we need a detailed, computerized algorithm that defines valid and invalid relationships between main diagnosis and underlying cause. Such an algorithm might be based on the decision tables' (tables specifying relationships between conditions and used for the selection of the underlying cause of death), developed by the US National Center for Health Statistics.29 With this done, the error pattern for both types of certificatesvalid and invalid relationshipscould be investigated, for example by means of checking the death certificates against the medical records. The possible benefits for the mortality statistics could then be estimated.
Diagnostic information concerning hospital deaths is currently reported both to the local hospital discharge register and, via the death certificate, to the national cause-of-death register. It might be tempting to relieve physicians of some of their administrative burden by replacing the customary certification of death by an extract from the hospital discharge record. However, this study illustrates that in spite of the obvious relationship between the two registers they remain essentially different: the death certificate gives a case history, while the hospital discharge record provides a snapshot. Hospital discharge records and death certificates supplement each other, in that some conditions likely to be absent from one of the registers will presumably be found in the other. Suppressing either of the two sources of information would cause severe disruption of statistical trends and a serious impoverishment of basic epidemiological data.
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Acknowledgments |
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References |
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2 Maudsley G, Williams EMI. Inaccuracy in death certificationwhere are we now? J Public Health Med 1996;18:5966.[Abstract]
3 Moriyama IM. Problems in measurement of accuracy of cause-of-death statistics. Am J Public Health 1989;79:134950.[ISI][Medline]
4 Kircher T. The autopsy and vital statistics. Hum Pathol 1990;21:16673.[ISI][Medline]
5 Kelson MC, Farebrother M. The effect of inaccuracies in death certification and coding practices in the European Economic Community (EEC) on international cancer mortality statistics. Int J Epidemiol 1987;16:41114.[Abstract]
6 NOMESCO (Nordic Medicostatistical Committee). Coordination of Mortality Statistics in the Nordic CountriesRequirements and Suggestions. NOMESCO Report 51:1998 (in Swedish).
7 Balkau B, Jougla E, Papoz L, Eurodiab Subarea C Study Group. European study of the certification and coding of six clinical case histories of diabetic patients. Int J Epidemiol 1993;22:11626.[Abstract]
8 Jougla E, Papoz L, Balkau B, Maugin P, Hatton F, Eurodiab Subarea C Study Group. Death certificate coding practices related to diabetes in European countriesThe EURODIAB Subarea C Study. Int J Epidemiol 1992;21:34351.[Abstract]
9 Gissler M, Kauppila R, Meriläinen J, Toukomaa, Hemminki E. Pregnancy-associated deaths in Finland 19871994definition problems and benefits of record linkage. Acta Obstr Gynecol Scand 1997;76:65157.[ISI][Medline]
10 Nyström L, Larsson LG, Rutqvist LE et al. Determination of cause of death among breast cancer cases in the Swedish randomized mammography screening trials. A comparison between official statistics and validation by an endpoint committee. Acta Oncol 1995;34:14552.[ISI][Medline]
11 Melinder K, Andersson R. Differences in injury mortality between the Nordic countrieswith special reference to differences in coding practices. Scand J Soc Med 1998;26:19097.[ISI][Medline]
12 Granquist L, Kovar JG. Editing of survey data: how much is enough? In: Survey Measurement and Process Quality. New York: Wiley, 1997, pp.41535.
13 Winkler WE. Problems with Inliers. Statistical Commission and Economic Commission for Europe. ECE/STAT/WS/97/82 GE.97-31639.
14 de Faire U, Friberg L, Lorich U, Lundman T. A validation of cause-of-death certification in 1156 deaths. Acta Med Scand 1976;200:22328.[ISI][Medline]
15 Alderson MR, Meade TW. Accuracy of diagnosis on death certificates compared with that in hospital records. Brit J Pre Soc Med 1967;21: 2229.
16 Gittelson AM, Senning J. Studies on the reliability of vital and health records: I. Comparison of cause of death and hospital record diagnoses. Am J Public Health 1979;69:68089.[Abstract]
17 Stegmayr B, Asplund K. Measuring stroke in the population: quality of routine statistics in comparison with a population-based stroke registry. Neuroepidemiology 1992;11:20413.[ISI][Medline]
18 Weng C, Coppini DV, Sönksen PH. Linking a hospital diabetes database and the National Health Service Central Register: a way to establish accurate mortality and movement data. Diabet Med 1997; 14:87783.[ISI][Medline]
19 O'Hara D, Hart W, Robinson M, McDonald I. Mortality soon after discharge from a major teaching hospital: linking mortality and morbidity. J Qual Clin Pract 1996;16:3948.[Medline]
20 Barchielli A, Buiatti E, Galanti C, Giovanetti L, Acciai S, Lazzeri V. Completeness of AIDS reporting and quality of AIDS death certification in Tuscany (Italy): a linkage study between surveillance system of cases and death certificates. Eur J Epidemiol 1995;11: 51317.[ISI][Medline]
21 Fugelstad A. Drug-related Deaths in Stockholm During the Period 19851994. Causes and Manners of Death in Relation to Type of Drug Abuse, HIV-infection and Methadone Treatment. 1997, Institution of Oncology-Pathology, Department of Forensic Medicine, Karolinska Institute, and Institution of Clinical Neuroscience, Department of Psychiatry, S:t Görans Hospital, Stockholm, Sweden. Thesis.
22 Goldacre MJ. Cause-specific mortality: understanding uncertain tips of the iceberg. J Epidemiol Community Health 1993;47:49196.[Abstract]
23 Centre for Epidemiology, National Board of Health and Welfare. The Swedish Hospital Discharge Register 19871995. Stockholm, 1997.
24 Blomqvist P, Ekbom A, Carlsson P, Ahlstrand C, Johansson JE. Benign prostatic hyperplasia in Sweden 1987 to 1994: changing patterns of treatment, changing patterns of cost. Urology 1997;50:21420.[ISI][Medline]
25 Socialstyrelsen [Swedish National Board of Health and Welfare]. KS87 [Swedish Version of International Classification of Diseases, Ninth Revision]. Stockholm, 1986.
26 Statistiska centralbyrån [Statistics Sweden]. Klassificering av dödsorsaker i svensk statistik [Classification of Causes of Death in Swedish Statistics]. Reports on Statistical Co-ordination 1990:3 (in Swedish).
27 World Health Organization. Medical Certification of Cause of Death. Instructions for Physicians on Use of International Form of Medical Certificate of Cause of Death. Geneva: WHO, 1979.
28 Nilsson AC et al. Slutenvårdsregistrets tillförlitlighet [The reliability of the Hospital Discharge Register]. Läkartidningen 1994;91:598605 (in Swedish).[Medline]
29 National Center for Health Statistics. The Mortality Medical Data System, MICAR, ACME and TRANSAX. NCHS, 1990.