Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
Mortality Trend in a Rapidly Developing Economy in Taiwan Part II: Life Expectancy and "Potential Years of Life Lost"
Shan P Tsai, PhD* CP Wen, MD, DrPH* JP Guo, MPH** SF Tsai, MPH** 'University of Texas School of Public Health Houston, Texas 77225, USA "Institute of Biomedical Sciences Academia Sinica, Taipei, Taiwan, ROC
Abstract Taiwan has made remarkable economic progress in the last 30 years. The life expectancy of its population improved steadily during this period. A male child born in 1983 could look forward to 70.4 years of life and a female child to 75.3 years, gains of 17.5 years and 19.0 years, respectively, since 1950. The potential gains in life expectancy of the Taiwan population are also examined if the five leading causes of death are reduced or eliminated. In addition, this paper discusses the concept of potential productive years of life lost (PYLL), examines the leading causes of premature death and shows how this measure can be used to target prevention programs and health care planning.
Key words: Life expectancy, potential productive years of life lost, Taiwan, Japan, United States. In an earlier paper' w e examined the changing mortality pattern of Taiwan and compared it to that of the U.S.A. and Japan. Commensurate with economic achievement, general improvement of overall mortality was observed, along with some untoward health effects of rapid development. Some of these untoward effects warrant further examination so that their impact can be minimized. This paper will attempt to characterize the life shortening features of selected major causes of death and explore the preventability of premature mortality. With the use of life table analysis and calculation of potential years of life lost (PYLL), the leading causes of premature mortality will be ranked, 49
Asia-Pacific Journai of Public Health 1991-Vol 5 No 1
and the impact of reduction or elimination of certain cause(s) of death on life expectancy will be assessed. Method The basic data sources for this study were from the official publication of vital statistics in Taiwan for 1983.' Life expectancy was calculated using a method developed by Chiang3 The potential gains in life expectancy by reduction of major causes of death were calculated according to Tsai et al? Potential years of life lost (PYLL) for a particular cause was calculated by summing the number of deaths at each age (between I and 70 years) multiplied by the remaining years of life up to age 70.s Total PYLL was calculated from the overall mortality. Percent of PYLL was the proportion of total PYLL attributed to a particular cause. In consideration of the current life expectancy in Taiwan and the increasing trend of delaying retirement age, 70 was selected as the cutoff year of productive life instead of age 65. Infant deaths (deaths of children less than 1 year of age) were excluded from the PYLL calculation because of their large number and because each infant death would account for 70 years lost, giving a heavy weight for this group, Further, from the preventive standpoint, the etiology of infant deaths is vastly different from that of deaths occurring later in life and is usually treated separately as an index of health statistics. The causes of death considered in this paper and their classification according to ICD-g6 are: cancer (ICD 140-208), diseases of circulatory system (390-459), stroke (430-438), a11 heart diseases (390459), infectious diseases (001-139), accidents (E800E949), diseases of liver (cancer and cirrhosis) (155, 571), tuberculoses (010-018), respiratory diseases (460-5 19), motor vehicle accidents (ES00-E8 19), and suicide (E950-E959). Table 1. Trend in Life Expectancy at Various Ages, Taiwan, 1950 - 83 Calender Year
1950 1955 1960 . 1965 , 1970 1975 1980 1983
50
Elact Age (in Sears)
Results Life E.vpectaiq In 1983, Taiwanese males had a life expectancy of 69.9 years, while females had a life expectancy of 75.1 years (Table 1). The corresponding figures were 73.8 years and 79.6 years for Japan and 71.7 years and 78.7 years for the U.S., respectively. The gender differential in life expectancy for Taiwan (5.2 years) was smaller than that of Japan (5.8 years) or the U.S. (7.0 years). Between 1950 and 1983 life expectancy at birth in Taiwan increased 17.5 years for males and 19.0 years for females. While life expectancy at age 45 increased approximately 7 years for both males and females during this period, the respective gain at age 65 was 3.7 years for males and 2.9 years for females. Eliriiiii~tiort of Selected Calms of Denrli The relative importance of various causes of death can be measured by the gain in life expectancy if a specific cause of death is eliminated. The calculation is based on the competing risks assumption that individuals would still be subject to the risk of other causes if the risk concerned is eliminated. The potential gain in life expectancy at birth of the Taiwanese population as a result of elimination of diseases of the circulatory system was 4.9 years for males and 5.6 years for females (Table 2). If it was possible to eliminate cancer as a cause of death, the average length of life would be increased by 2.3 years for males and 1.9 years for females. The human life wasted by accidents was estimated to be 2.2 years for males and 1.0 years for females. It is noteworthy that eliminating stroke would have less of an effect
Table 2. Life Expectancy Gain at Birth by Reducing Selected Causes of Death in Taiwan, 1983 Causes of Death
Percent Reduction 204
0 45 65 Males Females hlales Females hlales Females 22.3 25.9 52.9 ' 56.3 10.2 12.9 59.9 65.0 24.0 28.8 10.5 13.8 61.8 67.1 25.0 29.1 10.8 13.4 .61.5 70.0 26.4 30.4 11.9 14.3 66.1 71.2 26.8 30.7 11.9 14.4 68.3 73.3 28.0 31.7 12.5 14.9 74.5 28.8 69.6 32.2 13.5 . 15.7 75.3 29.3 32.7 15 8 70.4 13.9
Infectious diseases Cancer Circulatory system Stroke
50% Male Female 0.27 0.16
Male Female 0.55 0.33
100%
Male
Female
0.11
0.07
0.44 0.76
0.36
1.12 2.05
0.92
2.32
1.89
0.84
2.30
4.87
5.64
0.38
0.42
0.98
1.08
2.09
2.32
1.10 .. . 2.74
0.47
2.23
0.95
2.64
6.90
6.95
Accidents
0.44
0.19
All other causes
1.00
0.95
Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
than either cancer or accidents among males (2.1 years) but not among females (2.3 years).
Recliiction in Selected Causes of Death The results of reduction in selected causes of death are also presented in Table 2. If diseases of the circulatory system were reduced by 5096, the gain for females would be slightly higher than for males (2.3 years vs 2.1 years). On the other hand, gender differentials in life expectancy increases at birth are clearly indicated by the reduction of accidents. There were no appreciable gender differences in added years of life for the remaining causes of death. The years of life gained by a 50% reduction are about one-half the years gained by a 100% elimination of cancer, infectious diseases, stroke and accidents, but the gains by a 50% reduction of diseases of the circulatory system and all other causes are less than one-half of the gain expected by a 100% elimination. Poteiitial Years of Life Lost (PYLL) Between the ages of 1 and 70, there were 36,075 deaths among males in 1983 representing a cumulative total of 737,205 years of potentially productive life lost before they could reach age 70. There were 17,314 female deaths with a cumulative total of 353,780 years of productive life lost. It should be noted from the outset that there were more than twice the number of deceased males as deceased females and correspondingly twice the number of PYLL for males than females. PYLL was calculated for each cause of death and its proportion to total PYLL was expressed as percent of PYLL. The percent of PYLL and the proportion of deaths attributed to particular causes are shown in Table 3. Accidents accounted for 37.2% of PYLL for males and 24.9% for females. They were by far the leading cause for the most number of years of life lost. This is in contrast to the traditional ranking of causes of mortality in which accidents are third behind cancer and stroke. Similarly, suicide accounted for 2.6% and 2.5% of deaths but for 4.4% and 6.5% of PYLL for males and females, respectively. When accidents were divided into those caused by motor vehicles and nonmotor vehicles, males had more PYLL from motor vehicle accidents, while females had more PYLL from nonmotor vehicle accidents. If cancer is considered as a single entity (which it should not be), it would have ranked a distant second as a cause of premature mortality for males, contributing 15.9% of PYLL. The corresponding figure for females was much larger (20.4%). Liver disease, including liver cancer and cirrhosis of the liver, ranked third
Table 3. Percent of Productive Years of Life Lost (% of PYLL) and Proportion of Death (% of PD), Age 1-70, Taiwan, 1983 Cause of Death
% of PYLL
5% of PD
hlale
Female
hlale
Female
Cancer
15.94
20.4%
18.3%
16.1%
Strohe
6.3%
8.74
16.1%
19.0% 7.9%
37.24
24.9%
15.5%
hlotor Vehicle
18.8%
10.9%
8.0%
3.64
Nonniotor Vehicle
18.4%
14.0%
7.5%
4.3%
Accidents
All Heart Diseases
8.34
7.6%
14.5%
17.7%
Liver Cancer & Cirrhosis
9.6%
4.1%
9.4%
4.2%
Tuberculosis
1.8%
1.6%
3.2%
1.6%
Respiratory Diseases
3.6%
4.3%
8.5%
6.8%
Suicide
4.4%
6.5%
2.6%
2.5%
Infectious Diseases
6.6%
7.4%
10.5%
9.49
for males, representing 9.6% of PYLL. For females, stroke ranked third, contributing 8.7% of total PYLL, while liver disease only contributed 4.1%. Among males, stroke ranked sixth with 6.3% of PYLL. Conditions occurring among younger people rank more highly according to the PYLL measure than in conventional proportions of causes of death. The PYLL measure deemphasizes conditions responsible for a large proportion of deaths later in life (Table 3). Stroke, all heart diseases, and infectious diseases fall substantially in the PYLL ranking.
Discussion Among the available indices of health status, mortality statistics are most frequently used for descriptive purposes in order to prioritize the relative importance of various causes of death. This is because mortality data are the most readily available, are of reasonable quality and completeness and can be easily standardized and made comparable 'throughout time and place. In addition, death is the final outcome of all health measures and may represent the failure or success of medical services in the preventive or curative domain. Age-adjusted death rates, as described in Part I of this paper,' are the most important descriptive statistics and will continue to be used to describe and evaluate the outcome of public health programs and goals. However, exclusive reliance on these indices will not and cannot reflect the relative importance of premature mortality versus senile mortality. For example, more than 5070 of deaths
Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
in Taiwan occur after 65 years of age resulting from the underlying disease processes of the elderly and do not reflect the relative importance Of premature mortality. The indicator of PYLL has been developed primarily to quantify the relationship between mortality and potential economic productivity. It provides a more accurate picture of premature mortality by weighting deaths occurring at younger ages more heavily than those occurring in older persons. The PYLL concept has become increasingly popular and appropriate since improvement in health seems to stem primarily from prevention. While there have been various ways of calculating PYLL,S'" this paper assumes any death before the age of 70 as being a life lost prematurely. The earlier it occurs, the greater the loss to society. Percent of PYLL is a simple concept, relatively easy to calculate and understand. It provides an excellent yardstick in prioritizing preventive measures from a productivity standpoint. In a country obsessed with economic progress, percentage of PYLL should be a term understood by economic planners. Males lost more than twice the number of productive years as females in Taiwan. In other words, loss of productivity was twice as great among males, a stem reality not hitherto noticed. A large portion of this loss came from accidents. In the percent of PYLL analysis, accidents were by far the leading cause of potentially productive years of life lost. Almost an equal number of productive years was lost between motor vehicle and nonmotor vehicle accidents. The importance of the latter, those that occur at home and the workplace, has not been fully appreciated using conventional mortality statistics. It is, however, dramatically illustrated here. The threat of these home and workplace accidents warrants major efforts in both research and public education. The surprising finding is not so much that accidents were the leading cause of premature deaths since this is also true in countries such as the U . S 8 and Japan,' but rather that the magnitude of accidents and the proportion they contribute to PYLL were so large (37% for males and 25% for females). In comparison, the corresponding figures for Japan are 17.4% and 8.7% for males and females, respectively and for the U.S. is 25% (males and females combined). If accidents were reduced by only 25% in Taiwan, a realistically achievable target in a few years, the gain in productive years would be a significant number, equivalent to that from eliminating all heart diseases, an almost impossible task. While there was a far greater number of deaths 52
from both cancer and stroke than from accidents, the percent of PYLL attributed to the first two was much lower, with only one-half or one-third of the impact of that due to accidents. Cancer contributed 15.9% to total PYLL for males and 16.2% for females, while stroke contributed 6.3% for males and 8.7% for females. Overall, accidents are responsible for more productivity loss than cancer and stroke combined. In addition to accidents, the tragic importance of suicide among females is highlighted by its contribution of 6.5% to PYLL, which is relatively close to the 8.7% due to stroke. Suicide, however, constituted only 2.5% of all deaths among females, while stroke contributed to 19% of deaths. One of the most improved health indicators in Taiwan is the lengthening of life expectancy, particularly at birth. In a period of 33 years, males gained 17.5 years and females 19.0 years at age zero. The secular gains in life expectancy decrease with increasing age. This is because much of the increase in life expectancy was primarily the result of a reduction in infant mortality rather than progress made in old age. The gender differential for life expectancy at birth in 1983 was 4.9 years in favor of women but narrowed to 1.9 years by age 65. In Japan, the differential at birth is 5.8 years but declines to 3.1 years by age 65.7 This difference reflects a much higher female mortality among elderly in Taiwan than in Japan. The hypothetical elimination of a single cause of death is not only an interesting academic exercise but also an useful method to prioritize public health programs based on the extent of potential gain in life expectancy. The results from this type of analysis have implications for practical decision making in establishing health goals, allocating resources and evaluating health problems."*'2 Because of the existence of competing risks such that people continue to be subject to the risks of the remaining causes of death, the gain in life expectancy is not as large as one would expect. If all cancers were eliminated from human suffering, the gain in life expectancy would be approximately two years. The elimination of stroke would produce a slightly longer life expectancy than the elimination of cancer for females but not for males. The most interesting finding is that the elimination of accidents would have as much of an effect as the elimination of cancer, particularly among males. This provides an overwhelming argument for setting higher priority on accident prevention since it is more achievable and requires less resources compared to the herculean task of cancer elimination.
Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
To eliminate any cause of death is next to impossible, a more realistic goal would be a reduction of each cause of mortality to variable levels based on state of the art and logistic considerations in formulating prevention objectives. For example, a 20% reduction of cancer, a 20% reduction of stroke and a 50% reduction of accidents could yield at least an additional 1.9 years for males and 1.3 years for females. Such a goal is not unrealistic and could be realized in 5 to 10 years, whereas a similar gain through eliminating cancer is probably not attainable in the foreseeable future. Mortality seems to be one of the best measures to determine national priorities for public health problems. However, there are different ways niortality data can be presented and different emphases placed. For example, resulting priorities can be vastly different if analysis is based on deaths that are rapidly increasing, deaths that are not decreasing as fast as they should, deaths that are most preventable, deaths that have the greatest psychological impact on society, deaths that mostly affect economic productivity in society or deaths that contribute to the most premature mortality. In this and previous papers, most of these parameters have been examined. A convincing case can be made that causes of death that contribute most to premature mortality or those that deprive society of the most productive years of life should warrant the most attention. From an economic standpoint, efforts to reduce the productive years of life lost would be most beneficial. In summary, the prevention of both motor vehicle and nonmotor vehicle accidents should clearly be the top priority of all preventive programs. No medical efforts could accomplish as much as what accident prevention could, Cancer prevention is second in importance but obviously much more difficult to accomplish. Although stroke involves more older people and the number of suicides is small (primarily among young people), they contribute relatively large proportions of PYLL. Stroke and suicide are logistically more preventable and deserve the next level of preventive efforts. Suicide, reflecting the inadequacy of society in coping with those crying for help, could prove to be most rewarding in its reduction.
Acknowledgement The authors thank April Richardson for her skillful typing. References 1. Tsai SP, Wen CP: Mortality Trend in a Rapidly Developing Economy--in Taiwan. Part 1. Comparison with the U.S. and Japan, 1973-1983. Asia-Pacific Journal Public Health 1989; 3:41-50. 2. Department of Health, Executive Yuan, Taiwan Provincial Health Department. Health Statistics 1. General Health Statistics. Republic of China, 1983. 3. Chiang, CL: Introduction to Stochastic Process in Biostatistics. New York: John Wiley and Sons, 1968. 4. Tsai SP,Lee ES,Hardy RJ: The Effect of a Reduction in Leading Causes of Death: Potential Gains in Life Expectancy. American Journal of Public Health 1978;
681966-971. 5. Romeder JM, McWhinnie JR: Potential Years of Life Lost between Ages 1 and 70: An Indicator of Premature Mortality for Health Planning. lnternational Journal of Epidemiology 1977; 6:143-151. 6. World Health Organization: Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Deaths. Geneva: WHO, 1977. 7. Ministry of Health and Welfare: Vital Statistics. Vol 1-3,Japan, 1983. 8. National Center for Health Statistics, 1983. DHHS Pub. No. (PHS) 86-1232.Public Health Service. Washington, D.C.: US. Government Printing Office, 1985. Perloff JD,LeBaily SA, Kletke PR. Budetti PP, Connelly 9. JP: Premature death in the United States: Years of life lost and health priorities. Journal of Public Health Policy I 984; 5:167-184. 10. Centers for Disease Control. Premature mortality in the United States: Public health issues in the use of years of potential life lost. MMWR 1986;35 (suppl. no. 25). 11. Hickman JC, Esteil RJ: On the use of partial life expectancy in setting health goals. American Journal of Public Health 1969; 59:2243-2250. 12. Lew EA, Seltzer F:. Uses of the life table in public health. Milbank Memorial Fund Quarferly 1970; 48: 15-37.
53
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Mortality Trend in a Rapidly Developing Economy in Taiwan Part II: Life Expectancy and "Potential Years of Life Lost"
Shan P Tsai, PhD* CP Wen, MD, DrPH* JP Guo, MPH** SF Tsai, MPH** 'University of Texas School of Public Health Houston, Texas 77225, USA "Institute of Biomedical Sciences Academia Sinica, Taipei, Taiwan, ROC
Abstract Taiwan has made remarkable economic progress in the last 30 years. The life expectancy of its population improved steadily during this period. A male child born in 1983 could look forward to 70.4 years of life and a female child to 75.3 years, gains of 17.5 years and 19.0 years, respectively, since 1950. The potential gains in life expectancy of the Taiwan population are also examined if the five leading causes of death are reduced or eliminated. In addition, this paper discusses the concept of potential productive years of life lost (PYLL), examines the leading causes of premature death and shows how this measure can be used to target prevention programs and health care planning.
Key words: Life expectancy, potential productive years of life lost, Taiwan, Japan, United States. In an earlier paper' w e examined the changing mortality pattern of Taiwan and compared it to that of the U.S.A. and Japan. Commensurate with economic achievement, general improvement of overall mortality was observed, along with some untoward health effects of rapid development. Some of these untoward effects warrant further examination so that their impact can be minimized. This paper will attempt to characterize the life shortening features of selected major causes of death and explore the preventability of premature mortality. With the use of life table analysis and calculation of potential years of life lost (PYLL), the leading causes of premature mortality will be ranked, 49
Asia-Pacific Journai of Public Health 1991-Vol 5 No 1
and the impact of reduction or elimination of certain cause(s) of death on life expectancy will be assessed. Method The basic data sources for this study were from the official publication of vital statistics in Taiwan for 1983.' Life expectancy was calculated using a method developed by Chiang3 The potential gains in life expectancy by reduction of major causes of death were calculated according to Tsai et al? Potential years of life lost (PYLL) for a particular cause was calculated by summing the number of deaths at each age (between I and 70 years) multiplied by the remaining years of life up to age 70.s Total PYLL was calculated from the overall mortality. Percent of PYLL was the proportion of total PYLL attributed to a particular cause. In consideration of the current life expectancy in Taiwan and the increasing trend of delaying retirement age, 70 was selected as the cutoff year of productive life instead of age 65. Infant deaths (deaths of children less than 1 year of age) were excluded from the PYLL calculation because of their large number and because each infant death would account for 70 years lost, giving a heavy weight for this group, Further, from the preventive standpoint, the etiology of infant deaths is vastly different from that of deaths occurring later in life and is usually treated separately as an index of health statistics. The causes of death considered in this paper and their classification according to ICD-g6 are: cancer (ICD 140-208), diseases of circulatory system (390-459), stroke (430-438), a11 heart diseases (390459), infectious diseases (001-139), accidents (E800E949), diseases of liver (cancer and cirrhosis) (155, 571), tuberculoses (010-018), respiratory diseases (460-5 19), motor vehicle accidents (ES00-E8 19), and suicide (E950-E959). Table 1. Trend in Life Expectancy at Various Ages, Taiwan, 1950 - 83 Calender Year
1950 1955 1960 . 1965 , 1970 1975 1980 1983
50
Elact Age (in Sears)
Results Life E.vpectaiq In 1983, Taiwanese males had a life expectancy of 69.9 years, while females had a life expectancy of 75.1 years (Table 1). The corresponding figures were 73.8 years and 79.6 years for Japan and 71.7 years and 78.7 years for the U.S., respectively. The gender differential in life expectancy for Taiwan (5.2 years) was smaller than that of Japan (5.8 years) or the U.S. (7.0 years). Between 1950 and 1983 life expectancy at birth in Taiwan increased 17.5 years for males and 19.0 years for females. While life expectancy at age 45 increased approximately 7 years for both males and females during this period, the respective gain at age 65 was 3.7 years for males and 2.9 years for females. Eliriiiii~tiort of Selected Calms of Denrli The relative importance of various causes of death can be measured by the gain in life expectancy if a specific cause of death is eliminated. The calculation is based on the competing risks assumption that individuals would still be subject to the risk of other causes if the risk concerned is eliminated. The potential gain in life expectancy at birth of the Taiwanese population as a result of elimination of diseases of the circulatory system was 4.9 years for males and 5.6 years for females (Table 2). If it was possible to eliminate cancer as a cause of death, the average length of life would be increased by 2.3 years for males and 1.9 years for females. The human life wasted by accidents was estimated to be 2.2 years for males and 1.0 years for females. It is noteworthy that eliminating stroke would have less of an effect
Table 2. Life Expectancy Gain at Birth by Reducing Selected Causes of Death in Taiwan, 1983 Causes of Death
Percent Reduction 204
0 45 65 Males Females hlales Females hlales Females 22.3 25.9 52.9 ' 56.3 10.2 12.9 59.9 65.0 24.0 28.8 10.5 13.8 61.8 67.1 25.0 29.1 10.8 13.4 .61.5 70.0 26.4 30.4 11.9 14.3 66.1 71.2 26.8 30.7 11.9 14.4 68.3 73.3 28.0 31.7 12.5 14.9 74.5 28.8 69.6 32.2 13.5 . 15.7 75.3 29.3 32.7 15 8 70.4 13.9
Infectious diseases Cancer Circulatory system Stroke
50% Male Female 0.27 0.16
Male Female 0.55 0.33
100%
Male
Female
0.11
0.07
0.44 0.76
0.36
1.12 2.05
0.92
2.32
1.89
0.84
2.30
4.87
5.64
0.38
0.42
0.98
1.08
2.09
2.32
1.10 .. . 2.74
0.47
2.23
0.95
2.64
6.90
6.95
Accidents
0.44
0.19
All other causes
1.00
0.95
Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
than either cancer or accidents among males (2.1 years) but not among females (2.3 years).
Recliiction in Selected Causes of Death The results of reduction in selected causes of death are also presented in Table 2. If diseases of the circulatory system were reduced by 5096, the gain for females would be slightly higher than for males (2.3 years vs 2.1 years). On the other hand, gender differentials in life expectancy increases at birth are clearly indicated by the reduction of accidents. There were no appreciable gender differences in added years of life for the remaining causes of death. The years of life gained by a 50% reduction are about one-half the years gained by a 100% elimination of cancer, infectious diseases, stroke and accidents, but the gains by a 50% reduction of diseases of the circulatory system and all other causes are less than one-half of the gain expected by a 100% elimination. Poteiitial Years of Life Lost (PYLL) Between the ages of 1 and 70, there were 36,075 deaths among males in 1983 representing a cumulative total of 737,205 years of potentially productive life lost before they could reach age 70. There were 17,314 female deaths with a cumulative total of 353,780 years of productive life lost. It should be noted from the outset that there were more than twice the number of deceased males as deceased females and correspondingly twice the number of PYLL for males than females. PYLL was calculated for each cause of death and its proportion to total PYLL was expressed as percent of PYLL. The percent of PYLL and the proportion of deaths attributed to particular causes are shown in Table 3. Accidents accounted for 37.2% of PYLL for males and 24.9% for females. They were by far the leading cause for the most number of years of life lost. This is in contrast to the traditional ranking of causes of mortality in which accidents are third behind cancer and stroke. Similarly, suicide accounted for 2.6% and 2.5% of deaths but for 4.4% and 6.5% of PYLL for males and females, respectively. When accidents were divided into those caused by motor vehicles and nonmotor vehicles, males had more PYLL from motor vehicle accidents, while females had more PYLL from nonmotor vehicle accidents. If cancer is considered as a single entity (which it should not be), it would have ranked a distant second as a cause of premature mortality for males, contributing 15.9% of PYLL. The corresponding figure for females was much larger (20.4%). Liver disease, including liver cancer and cirrhosis of the liver, ranked third
Table 3. Percent of Productive Years of Life Lost (% of PYLL) and Proportion of Death (% of PD), Age 1-70, Taiwan, 1983 Cause of Death
% of PYLL
5% of PD
hlale
Female
hlale
Female
Cancer
15.94
20.4%
18.3%
16.1%
Strohe
6.3%
8.74
16.1%
19.0% 7.9%
37.24
24.9%
15.5%
hlotor Vehicle
18.8%
10.9%
8.0%
3.64
Nonniotor Vehicle
18.4%
14.0%
7.5%
4.3%
Accidents
All Heart Diseases
8.34
7.6%
14.5%
17.7%
Liver Cancer & Cirrhosis
9.6%
4.1%
9.4%
4.2%
Tuberculosis
1.8%
1.6%
3.2%
1.6%
Respiratory Diseases
3.6%
4.3%
8.5%
6.8%
Suicide
4.4%
6.5%
2.6%
2.5%
Infectious Diseases
6.6%
7.4%
10.5%
9.49
for males, representing 9.6% of PYLL. For females, stroke ranked third, contributing 8.7% of total PYLL, while liver disease only contributed 4.1%. Among males, stroke ranked sixth with 6.3% of PYLL. Conditions occurring among younger people rank more highly according to the PYLL measure than in conventional proportions of causes of death. The PYLL measure deemphasizes conditions responsible for a large proportion of deaths later in life (Table 3). Stroke, all heart diseases, and infectious diseases fall substantially in the PYLL ranking.
Discussion Among the available indices of health status, mortality statistics are most frequently used for descriptive purposes in order to prioritize the relative importance of various causes of death. This is because mortality data are the most readily available, are of reasonable quality and completeness and can be easily standardized and made comparable 'throughout time and place. In addition, death is the final outcome of all health measures and may represent the failure or success of medical services in the preventive or curative domain. Age-adjusted death rates, as described in Part I of this paper,' are the most important descriptive statistics and will continue to be used to describe and evaluate the outcome of public health programs and goals. However, exclusive reliance on these indices will not and cannot reflect the relative importance of premature mortality versus senile mortality. For example, more than 5070 of deaths
Asia-Pacific Journal of Public Health 1991-Vol 5 No 1
in Taiwan occur after 65 years of age resulting from the underlying disease processes of the elderly and do not reflect the relative importance Of premature mortality. The indicator of PYLL has been developed primarily to quantify the relationship between mortality and potential economic productivity. It provides a more accurate picture of premature mortality by weighting deaths occurring at younger ages more heavily than those occurring in older persons. The PYLL concept has become increasingly popular and appropriate since improvement in health seems to stem primarily from prevention. While there have been various ways of calculating PYLL,S'" this paper assumes any death before the age of 70 as being a life lost prematurely. The earlier it occurs, the greater the loss to society. Percent of PYLL is a simple concept, relatively easy to calculate and understand. It provides an excellent yardstick in prioritizing preventive measures from a productivity standpoint. In a country obsessed with economic progress, percentage of PYLL should be a term understood by economic planners. Males lost more than twice the number of productive years as females in Taiwan. In other words, loss of productivity was twice as great among males, a stem reality not hitherto noticed. A large portion of this loss came from accidents. In the percent of PYLL analysis, accidents were by far the leading cause of potentially productive years of life lost. Almost an equal number of productive years was lost between motor vehicle and nonmotor vehicle accidents. The importance of the latter, those that occur at home and the workplace, has not been fully appreciated using conventional mortality statistics. It is, however, dramatically illustrated here. The threat of these home and workplace accidents warrants major efforts in both research and public education. The surprising finding is not so much that accidents were the leading cause of premature deaths since this is also true in countries such as the U . S 8 and Japan,' but rather that the magnitude of accidents and the proportion they contribute to PYLL were so large (37% for males and 25% for females). In comparison, the corresponding figures for Japan are 17.4% and 8.7% for males and females, respectively and for the U.S. is 25% (males and females combined). If accidents were reduced by only 25% in Taiwan, a realistically achievable target in a few years, the gain in productive years would be a significant number, equivalent to that from eliminating all heart diseases, an almost impossible task. While there was a far greater number of deaths 52
from both cancer and stroke than from accidents, the percent of PYLL attributed to the first two was much lower, with only one-half or one-third of the impact of that due to accidents. Cancer contributed 15.9% to total PYLL for males and 16.2% for females, while stroke contributed 6.3% for males and 8.7% for females. Overall, accidents are responsible for more productivity loss than cancer and stroke combined. In addition to accidents, the tragic importance of suicide among females is highlighted by its contribution of 6.5% to PYLL, which is relatively close to the 8.7% due to stroke. Suicide, however, constituted only 2.5% of all deaths among females, while stroke contributed to 19% of deaths. One of the most improved health indicators in Taiwan is the lengthening of life expectancy, particularly at birth. In a period of 33 years, males gained 17.5 years and females 19.0 years at age zero. The secular gains in life expectancy decrease with increasing age. This is because much of the increase in life expectancy was primarily the result of a reduction in infant mortality rather than progress made in old age. The gender differential for life expectancy at birth in 1983 was 4.9 years in favor of women but narrowed to 1.9 years by age 65. In Japan, the differential at birth is 5.8 years but declines to 3.1 years by age 65.7 This difference reflects a much higher female mortality among elderly in Taiwan than in Japan. The hypothetical elimination of a single cause of death is not only an interesting academic exercise but also an useful method to prioritize public health programs based on the extent of potential gain in life expectancy. The results from this type of analysis have implications for practical decision making in establishing health goals, allocating resources and evaluating health problems."*'2 Because of the existence of competing risks such that people continue to be subject to the risks of the remaining causes of death, the gain in life expectancy is not as large as one would expect. If all cancers were eliminated from human suffering, the gain in life expectancy would be approximately two years. The elimination of stroke would produce a slightly longer life expectancy than the elimination of cancer for females but not for males. The most interesting finding is that the elimination of accidents would have as much of an effect as the elimination of cancer, particularly among males. This provides an overwhelming argument for setting higher priority on accident prevention since it is more achievable and requires less resources compared to the herculean task of cancer elimination.
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To eliminate any cause of death is next to impossible, a more realistic goal would be a reduction of each cause of mortality to variable levels based on state of the art and logistic considerations in formulating prevention objectives. For example, a 20% reduction of cancer, a 20% reduction of stroke and a 50% reduction of accidents could yield at least an additional 1.9 years for males and 1.3 years for females. Such a goal is not unrealistic and could be realized in 5 to 10 years, whereas a similar gain through eliminating cancer is probably not attainable in the foreseeable future. Mortality seems to be one of the best measures to determine national priorities for public health problems. However, there are different ways niortality data can be presented and different emphases placed. For example, resulting priorities can be vastly different if analysis is based on deaths that are rapidly increasing, deaths that are not decreasing as fast as they should, deaths that are most preventable, deaths that have the greatest psychological impact on society, deaths that mostly affect economic productivity in society or deaths that contribute to the most premature mortality. In this and previous papers, most of these parameters have been examined. A convincing case can be made that causes of death that contribute most to premature mortality or those that deprive society of the most productive years of life should warrant the most attention. From an economic standpoint, efforts to reduce the productive years of life lost would be most beneficial. In summary, the prevention of both motor vehicle and nonmotor vehicle accidents should clearly be the top priority of all preventive programs. No medical efforts could accomplish as much as what accident prevention could, Cancer prevention is second in importance but obviously much more difficult to accomplish. Although stroke involves more older people and the number of suicides is small (primarily among young people), they contribute relatively large proportions of PYLL. Stroke and suicide are logistically more preventable and deserve the next level of preventive efforts. Suicide, reflecting the inadequacy of society in coping with those crying for help, could prove to be most rewarding in its reduction.
Acknowledgement The authors thank April Richardson for her skillful typing. References 1. Tsai SP, Wen CP: Mortality Trend in a Rapidly Developing Economy--in Taiwan. Part 1. Comparison with the U.S. and Japan, 1973-1983. Asia-Pacific Journal Public Health 1989; 3:41-50. 2. Department of Health, Executive Yuan, Taiwan Provincial Health Department. Health Statistics 1. General Health Statistics. Republic of China, 1983. 3. Chiang, CL: Introduction to Stochastic Process in Biostatistics. New York: John Wiley and Sons, 1968. 4. Tsai SP,Lee ES,Hardy RJ: The Effect of a Reduction in Leading Causes of Death: Potential Gains in Life Expectancy. American Journal of Public Health 1978;
681966-971. 5. Romeder JM, McWhinnie JR: Potential Years of Life Lost between Ages 1 and 70: An Indicator of Premature Mortality for Health Planning. lnternational Journal of Epidemiology 1977; 6:143-151. 6. World Health Organization: Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Deaths. Geneva: WHO, 1977. 7. Ministry of Health and Welfare: Vital Statistics. Vol 1-3,Japan, 1983. 8. National Center for Health Statistics, 1983. DHHS Pub. No. (PHS) 86-1232.Public Health Service. Washington, D.C.: US. Government Printing Office, 1985. Perloff JD,LeBaily SA, Kletke PR. Budetti PP, Connelly 9. JP: Premature death in the United States: Years of life lost and health priorities. Journal of Public Health Policy I 984; 5:167-184. 10. Centers for Disease Control. Premature mortality in the United States: Public health issues in the use of years of potential life lost. MMWR 1986;35 (suppl. no. 25). 11. Hickman JC, Esteil RJ: On the use of partial life expectancy in setting health goals. American Journal of Public Health 1969; 59:2243-2250. 12. Lew EA, Seltzer F:. Uses of the life table in public health. Milbank Memorial Fund Quarferly 1970; 48: 15-37.
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