Dr Ng Tze Pin, Department of Community, Occupational and Family Medicine, Faculty of Medicine, National University of Singapore, Medical Drive, Singapore. E-mail: cofngtp{at}nus.edu.sg
Abstract
Background Amenable mortality is used to assess the effects of health care services on gains in mortality outcomes. Possibly differing patterns of trends in amenable mortality may be expected in economically less developed countries, which have undergone rapid epidemiological transition and recent reforms in health care systems, but such studies are scarce. This study was set up to examine the trends in amenable mortality in Singapore from 1965 to 1994; to estimate the relative impact of medical care and primary preventive policy measures in terms of gains in mortality outcomes; to examine ethnic differences in amenable mortality among Chinese, Malays and Indians.
Methods Age-standardized mortality rates were calculated for 16 amenable causes of death in Singapore for six 5-year periods (19651969, ..., 19901994), and for each of the three main ethnic groups for three periods (19891991, 19921994, 1995 1997). Amenable mortality rates were divided into those which can be reduced by timely therapeutic care for treatable conditions (e.g. asthma and appendicitis), or by primary preventive measures for preventable conditions (e.g. lung cancer and motor vehicle injury).
Results Amenable mortality was higher in males (age-standardized rate 109.7 per 100 000 population) than in females (age-standardized rate 60.7 per 100 000 population). Amenable mortality declined by 1.77% a year in males and 1.72% a year in females. By comparison, the average yearly decline in non-amenable mortality was 0.91% in males and 1.17% in females. The decline in amenable mortality was largely due to treatable causes rather than a decline in mortality due to preventable causes of death. Amenable mortality was lowest for Chinese and highest for Malays. Over the recent 9-year period from 1989 to 1997, amenable mortality declined more in Chinese than in Malays and Indians. However, Indian females showed by far the sharpest decline, whereas Indian males, by contrast, showed an increase in amenable mortality, due to both treatable and preventable causes.
Conclusions In line with findings from European countries, amenable mortality in Singapore declined more than non-amenable mortality. There were more significant gains in mortality outcomes from medical care interventions than from primary preventive policy measures. Gender and ethnic differences in amenable mortality were also observed, highlighting issues of socioeconomic equities to be addressed in the financing and delivery of health care.
Keywords Outcome measures, quality of care
Accepted 19 July 2000
The concept of studying amenable mortality as a method of measuring the quality of health care was first introduced by the American Working Group on Preventable and Manageable Diseases in 1976.1 The method is based on the premise that the effectiveness of health care can be evaluated from mortality due to certain conditions which are wholly or substantially avoidable by timely and appropriate medical care interventions. In the 1980s and 1990s, the validity and applicability of using amenable mortality as outcome indicators of health care were demonstrated in various studies conducted in the UK, other Western European countries in the European Community, as well as Scandinavian countries such as Sweden and Finland.28 These studies adopted 16 amenable causes of death, developed by an EC working group, for which there is evidence that mortality rates can be reduced by timely therapeutic care for treatable conditions (e.g. as asthma and appendicitis), or by primary preventive measures for preventable conditions (e.g. lung cancer and motor vehicle injury).810 These amenable causes of death were used respectively as indicators of outcome of medical care, and as indicators of outcome of national health policy.
Time trend analyses in these studies have in general shown that amenable mortality has declined faster over the past decades than most other causes of death or overall mortality.57,11 Socioeconomic factors, as well as environmental exposures and nutrition, are likely to contribute to such declines in mortality, especially for non-amenable causes of death, but health care service is also responsible for part of the decline.12 The impact of health services, estimated by the differential in rates of mortality decline from amenable and non-amenable causes, has been reported to account for 50% of the total decline in mortality from amenable causes.7
Geographical variations in amenable mortality at national and international level,25 as well as among different social classes have also tested the application of amenable mortality studies in the evaluation of socioeconomic equity of the health care system.1317 There are, however, no studies that have examined ethnic variations in amenable mortality, although such studies are common in other areas of health care research.
Subsequent studies have been conducted in less economically developed countries, such as Eastern Europe and former Soviet republics.1820 These studies are of interest in shedding light on possible differing patterns of amenable mortality trends between countries with differing levels of economic development and health care systems. There are, however, virtually no studies in less economically developed countries in Asia which are characterized by rapid epidemiological transition and reforms in systems of health care financing and delivery.
Over the past four decades, the small island republic of Singapore (population about 3 million) has experienced rapid and significant economic development and improvement in health status. Having undergone a rapid epidemiological transition to a disease pattern that is now dominated by chronic degenerative conditions,21 it is uncertain how much health gains have been achieved through recent measures aimed at primary disease prevention. Health care reform policies since the 1980s have focused on making health care cost-effective and affordable;22 however, outcome data on medical care quality are largely lacking. Among the multi-ethnic population of Singapore (75% Chinese, 14% Malay and 7% Indian), previous studies have highlighted significant ethnic differences in health status. There are reasons to believe that, apart from intrinsic genetic and socioeconomic factors, much of these differences arise from environmental, behavioural and lifestyle factors that are amenable to primary preventive measures, and from medical care factors that are amenable to measures aimed at improving the delivery of quality medical care.
In the present study, we examined the trends in amenable mortality in Singapore from 1965 to 1994, with a view to assessing the effects of health care services on gains in mortality outcomes. We also sought to estimate the relative impact of medical care and primary preventive policy measures in terms of their actual reductions in mortality outcome. Finally we examined variations in amenable mortality among the three ethnic groups.
Methodology
Data on deaths and population for the period 19651994 were obtained from the Registry of Births, Death and Marriage and the Department of Statistics, Singapore.23,24 The register is based on the death certificate issued by doctors following the death of a Singaporean citizen or permanent resident. The certificate states the underlying cause of death according to the International Classification of Diseases (ICD-6, 8 and 9). Although there is some variability in the codes between ICD revisions, the changes are not considered significant enough to affect comparability of the data from different years (Table 1).
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The trends in age-standardized mortality by amenable, non-amenable, and all causes were analysed for consecutive 5-year periods (19651969, ..., 19901994). Ethnic differences in mortality rates were analysed for three periods (19891991, 19921994, 19951997), the years when routine statistics by ethnic groups were available. Direct standardization for age and sex was done using the 1990 census population as the standard population. The relative rates of decline in amenable and non-amenable mortality were compared by the standardized mortality ratios (SMR), using a base of 100 for the 1990 general population rates. Linear regression analysis with the year of death as independent variable and the logarithm of the standardized mortality ratio (SMR) as dependent variable was also done. The significance of the yearly change or the trend was then tested using the two-tailed t-test. The best model of the linear trends was based on R2 values (coefficient of determination). All statistical analyses were done using the SPSS statistical software.
In the absence of any direct effect of health care services on mortality, the rate of decline in amenable mortality may be assumed to be the same as that of non-amenable mortality.7 We have therefore used a proxy measure of the direct impact of health care in terms of gains in mortality outcome by calculating the differential percentage decline in amenable mortality after subtracting the percentage decline of non-amenable mortality.
Results
From 1965 to 1994 the number of amenable deaths in those aged 564 years (44 018 males and 23 563 females) constituted 42.9% of all male causes and 43.6% of all female causes. Treatable conditions in males and females accounted for 39.8% and 45.2% of amenable deaths, respectively (Table 2). In males, the amenable mortality as a proportion of all-cause mortality increased from 34.3% in the youngest age group (514 years) to 47.8% in the oldest age group (6064 years). In females, this proportion increased from 38.2% in the youngest age group (514 years) to 49.6% in the oldest age group (6064 years). Cerebrovascular disease (12 946 deaths), lung cancer (7256 deaths) and motor vehicle accidents (6727 deaths) accounted for the largest number of amenable deaths, while pneumonia contributed the most to mortality from treatable conditions (7269 deaths) (Table 1
). Amenable mortality was higher in males (age-standardized rate 109.7 per 100 000 population in 19901994) than in females (age-standardized rate 60.7 per 100 000 population in 19901994).
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By evaluating the decline in amenable mortality relative to the decline in non-amenable mortality, it would appear that there was a greater impact of health care on the male population than on the female population (Table 3).
The decline in amenable mortality was contributed to more by the decline in treatable mortality than the decline in preventable mortality. Between the periods from 19651969 to 19901994, treatable causes of death declined by 78.2% in males and 67.8% in females. By comparison, preventable causes of death declined by only 28.5% in males and 34.2% in females. This is most clearly shown by the relative declines in SMR of treatable and preventable causes of death in Figure 2.
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The greatest decline in treatable causes of death was observed for tuberculosis (108.7% in males and 107.6% in females) and appendicitis and hernia (110.4% in males and 114.2% in females). For preventable causes of death, the lack of a substantial decline was mainly explained by actual increases in death rates from colo-rectal cancers (36.0% in men and 38.1% in women) and lung cancer (14.1% in men).
Ethnic differences
Among the three ethnic groups in the population, Chinese had the lowest all cause mortality rate, whereas Indians had a slightly higher rate than Malays (Table 4). However, when amenable mortality was examined, Malays had the highest rates of mortality, followed by Indians, especially for treatable causes. For preventable causes, Indians had similar rates of mortality compared to Chinese.
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A principal finding of this study is that mortality due to amenable causes dropped more than mortality from non-amenable causes for both sexes. This pattern is similar to those observed in economically developed countries.68,11 Most of the decline in amenable mortality was attributable to treatable causes, not preventable ones. Amenable mortality from treatable causes declined at more than twice the rate of decline due to preventable causes. The gains in mortality outcome has, however, been most pronounced in the first two decades, and moderated in more recent periods.
Although preventable mortality declined over a 30-year study period by nearly 30% for both sexes, this was, however, not very different from the decline in non-amenable mortality, suggesting that the impact of primary preventive health care policy measures was rather limited. Individually, two causes of death in the preventable group, namely, malignant neoplasm of colon, rectum and recto-sigmoid junction and malignant neoplasm of trachea, bronchus and lung contributed most to the unfavourable trend in preventable mortality. Apart from these two conditions, mortality from preventable causes decreased more than non-amenable mortality for both sexes. Smoking and dietary habits that contributed to increases in these conditions during the 30-year period did not receive much attention until the late 1980s. The emphasis in public health from the 1950s to the 1970s was on environmental sanitation and the control of communicable diseases. Public health measures aimed at chronic disease prevention and promotion of healthy lifestyles were largely implemented in the 1980s. Since then, they have appeared to produce some results in reducing the prevalence and levels of behavioural risk factors in the population, but it will be probably another decade before their impact on reducing the incidence and mortality from cancer and chronic lifestyle-related diseases can begin to be apparent.
It is also worth noting that even though the percentage decline in amenable mortality was similar for both sexes, it would appear that health care had a more favourable impact on males than in females. Although pari passu, it is expected that health care should be of the quality that the impact is the same irrespective of gender differences, the percentage decline in death from some diseases was less in females than in males, a finding which parallels that in several previous studies on gender differences.7,8 The study in Sweden8 even showed an upward trend of mortality for this group of causes, especially asthma, among the female population.
We found important differences among the ethnic groups in mortality outcomes of primary preventive and curative health care interventions. To the best of our knowledge, this has not been studied by previous investigators. The best outcomes were seen for Chinese, in whom both the levels and rates of declines in amenable causes of death (both preventable and treatable) were most favourable. Although Malays had a higher level of amenable mortality compared to Indians, the rate of decline was in fact more favourable. Given that the recent period from 1989 to 1997 witnessed more moderate mortality declines, amenable mortality dropped faster than non-amenable mortality in this group, suggesting that Malays are currently achieving more gains from health care interventions than Chinese and Indians. Among Indians, amenable mortality from both preventable and treatable causes in fact increased in males. On the other hand, Indian females appeared to show extraordinary gains from health care interventions. Some data are available of the known determinants of health status differences among the three ethnic groups which explain the observed differences in the levels of amenable mortality. Apart from genetic factors which obviously contribute, socioeconomic status, smoking, alcohol consumption, diet, physical activity, obesity, accident risk, and health-seeking behaviour, including health care utilization, are known to be different among the ethnic groups in Singapore.25 The Chinese are the most affluent and educated ethnic population group in the country, and almost certainly have more access to better quality health care. The levels of smoking, obesity, cholesterol, alcohol, exercise, and dietary patterns are generally all unfavourable in Malays and Indians.25 We believe that health beliefs and cultural differences in health-seeking behaviour are most likely to explain why there are such disparities.
As in previous studies, empirical dichotomies of amenable and non-amenable causes of death, and of preventable and treatable causes of death were employed in this study. This allowed us to examine the impact of health care in its broadest sense, as well as through its component strategies of medical treatment and primary prevention. The strategies apply to causes of death which are amenable through curative measures, as well as by appropriate primary preventive measures for diseases, which are known to be not definitely curable through current medical interventions. The spontaneous decline in incidence of non-amenable causes is considered to be mostly attributable to the impact of general socioeconomic factors outside the health care system.
The selection of specific conditions into the rubric of amenable causes of death deserves to be reviewed. It may be justified to include coronary heart disease in this group in view of recent evidence about the effectiveness of thrombolytic therapy and other interventions. However, we were also aware that our evaluation dated back to 1965. The introduction of medical care technologies for coronary heart disease care including thrombolytic therapy, coronary artery bypass graft (CABG) and percutaneous transluminal coronary angioplasty (PTCA), and the evidence of their effectiveness, are of more recent origin. The selection of conditions was therefore based on the best evidence available at the time that an appropriate intervention would be effective in preventing death. Furthermore, we were interested in comparing amenable mortality outcome information with that already available in many Western countries. To make the comparison as valid as possible we therefore decided on having the same fixed selection of amenable causes of death.
There were changes in coding practice (from ICD-6 to ICD-9) over the period of study, however, previous other studies have shown that revisions are unlikely to be responsible for the observed trends.6 The accuracy of diagnostic labelling and coding could be possible causes of such overall variation in death rates for different time periods, but the effect of these causes was negligible (Table 1). In the present study, data based on yearly trends are subject to the effects of random fluctuations, and the change in mortality rate may also be non-linear. In assessing the statistical significance of trends, mortality trends were modelled by linear regression of the logarithm of the age-standardized mortality rates on calendar year. The use of logarithmic transformation improves the linear correlation. In most instances, the linear model was appropriate, and the use of non-linear (quadratic) modelling did not improve the fit significantly. This is evidenced by the trends in mortality rates across successive 5-year periods as presented in the Figures.
In conclusion, the present study indicates that health care interventions in Singapore over 30 years have had a significant impact in mortality outcomes. The gain in terms of mortality reduction from medical care appears to be greater than that from primary prevention. This has to be understood in the context of the rapid epidemiological and health care transition that has taken place. The gain from primary prevention was mostly offset by trends in lung cancer and colo-rectal cancer, which have yet to be reversed by recent initiatives in primary prevention. The study also highlights important gender and ethnic differences in the outcomes of health care that call attention to issues of socioeconomic equity in health care which would need to be addressed in the financing and delivery of health care.
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