Eur. J. Epidemiol. 0392-2990 November 1992, p. 875-877
EUROPEAN JOURNAL
Vol. 8, No. 6
OF EPIDEMIOLOGY BRIEF REPORTS
INFLUENCE OF DIFFERENT UPPER AGE LIMITS ON THE "YEARS OF POTENTIAL LIFE LOST" INDEX A. ORTEGA 1 and
M. PUIG
Basic Medical Sciences Department - School o f Medicine - Universidad de Barcelona San Lorenzo, 21 - 43201-Reus (Spain).
Keywords: Inter-study comparison - Life expectancy - Methodology - Mortality - Years of potential life lost The use of 65, 70 or 75 years as upper age limits for the "Years of Potential Life Lost" index (YPLL) could influence the relative importance assigned to different causes of premature death. Data from a representative year (1987) in Catalonia (Spain), show that health priorities and comparability among studies are not affected by the use of these upper age limits.
The mortality rates currently used in epidemiological studies (crude or age adjusted) provide information on the frequency of the different causes of death but, unless age-specific rates are calculated, give no indication of when these deaths occurred. From the socioeconomic and public health point of view, this information is of importance in assessing life expectancy. To address this problem, an index of lost life-expectancy has been developed that takes into account only those deaths occurring between 1 and 70 years of age; termed the "years of potential life lost" (YPLL) (10). Deaths in the first year of life are not included so as not to give excessive importance to congenital diseases. In 1982, the Centers for Disease Control (USA) began ranking the causes of premature death according to the YPLL. Health priorities ranked by this method were different from the traditional methods. The YPLL index showed that accidents together with cancer and heart disease accounted for the majority of YPLL before the age of 65 (2) and also indicated smoking, alcohol and unintended pregnancies as important causes of avoidable premature mortality and morbidity in the U.S. (7). 1 Corresponding author.
The concept of an YPLL index is widely accepted but the selection of its upper age of reference is debatable. The more common upper limit indicators are 65 (USA) (2, 8) or 70 years of age (Europe) (4, 5). Similarly, three other parameters: 75 years of age, the life expectancy at birth and the life expectancy at the age at which death occurs have also been used. These assessments raise concern regarding the comparability of different studies especially when the influence of this upper limit on the relative importance of the cause-ofdeath is not known. We have studied the effect of different upper limits on the YPLL index and on the relative importance of cause-of-death. Data were collated on deaths occurring in Catalonia, Spain (pop. 5,993,583) in the year 1987. Deaths recorded by age and cause were taken from the official publication of the Department of Health and Social Security of the Autonomous Government of Catalonia (3). The 46,977 death certificates issued (representing > 96% of all deaths in Catalonia in that year) had been coded at a three-digit level, applying the criteria of the International Classification of Diseases-9th revision (12). The YPLL were calculated from grouped data; the intervals used being 1-4, 5-14, 15-24, 25-34, 35-44, 45-54, 55-64 and 65-74 years of age.
875
Ortega A. and Puig M.
Eur. J. Epidemiol.
A uniform distribution_of deaths may be assumed within each of the earlier age intervals, but not necessarily so for the latter two. However, for the present purposes and in lieu of any other weighting procedures available, the assumption may be accepted, albeit none too rigorously, as an initial approach to quantification. Thus, the number of YPLL in a given interval was: (number of deaths) x (upper age limit - middle age of the interval). The upper age-limits were taken as 65, 70 and 75 years. The YPLL rates (per 1000 persons at risk) and the percentage of total YPLL for a given cause-of-death were also calculated. Table 1 shows the YPLL rates for the 12 main causes of death in Catalonia. They account for 75% of the total YPLL. For comparison, their mortality rates are also presented. Cancer was the leading cause of death at all ages in this study and accounted for one third of YPLL. Accidents and cardiovascular diseases were responsible for 150/0 and 11% of YPLL, respectively. Chronic liver diseases contributed approximately 6% of YPLL. The other six causes, in total, represented less than 12%. Cause-of-death ranking remained consistent, irrespective of the upper limit criteria used and despite the increasing YPLL rates. Only congenital abnormalities and homicides lost rank as the reference age increased, while diabetes increased its rank. All three accounted for less than 5% of YPLL and could be considered minor.
In terms of the proportional share of YPLL for the various causes of death, there was an increase for cancer, cardiovascular disease, chronic obstructive pulmonary diseases and diabetes with age. Conversely, the proportional share of YPLL of other causes such as traffic and non-traffic accidents, suicide, homicide and congenital abnormalities was inversely related to the age limit criteria. Verification of the quality of our death certificates was not feasible. However, this aspect has been previously addressed (6). In two Spanish validation studies - one in hospitals in Barcelona (9) and another a population-based study in Valencia (1) - into the underlying cause-of-death, the agreement indices for disease category between the original death certificate and the reference cause-of-death (determined by a panel of experts) were 70 and 80%, respectively well within the usual range of concordance for broad categories of 60 to 90% (1). Another monitor of the quality of the death certificate data is the percent of deaths attributed to a non-specific cause. In the data used, the category "ill-defined conditions" (group 16 of the International Classification of Diseases) had a mortality rate of 7.4 per 100,000 and an YPLL rate of 0.2 per 1000 before the age of 70; less than 1% in both cases. Hence, the validity of our death-certificate data is within acceptable terms.
TABLE 1. - Years of potential life lost rates for several causes-of-death in Catalonia (1987), using different upper reference ages. The crude mortality rates for these causes are also shown in deaths/100,000. Age
65
70
75
Deaths per
Causea
Rank
Rate b
(%)c
Rank
Rate
(%)
Rank
Rate
(%)
C TA HD CLD CVD NTA S COPD CA H D P, I
1 2 3 4 5 6 7 9 8 10 12 11 Other
8.8 3.7 1.6 1.5 1.0 0.9 0.8 0.4 0.5 0.4 0.2 0.2 6.9
(32.8) (13.8) (5.8) (5.4) (3.7) (3.3) (3.0) (1.5) (1.9) (1.4) (0.9) (0.8) (25.6)
1 2 3 4 5 6 7 8 9 10 11 12
13.2 4.3 2.6 2.2 1.7 1.0 1.0 0.7 0.5 0.4 0.4 0.4 9.3
(35.0) (11.4) (6.9) (5.7) (4.5) (2.8) (2.7) (1.9) (1.4) (1.2) (1.1) (1.0) (24.5)
1 2 3 4 5 7 6 8 10 12 9 11
19.1 4.9 4.2 3.1 2.8 1.2 1.2 1.2 0.7 0.6 0.5 0.5 12.7
(36.1) (9.4) (7.9) (5.8) (5.3) (2.3) (2.3) (2.3) (1.4) (1.2) (1.0) (1.0) (24.1)
Total
26.8
37.8
52.8
100,000 1 7 3 5 2 11 9 4 10 12 6 8
203.8 14.7 81.1 24.0 113.0 2.2 6.0 33.9 4.3 1.4 20.6 9.3 268.7
(%) (26) (2) (10) (3) (14) (< 1) (< 1) (4) (< 1) (< 1) (3) (1) (34)
783
aC: cancers; TA: traffic accidents; HD: heart disease; CLD:chronic liver disease and cirrhosis; CVD: cerebrovascular disease; NTA: non-traffic accidents; S: suicide; CA: congenital abnormalities; COPD: chronic obstructive pulmonary disease; H: homicide; P, I: pneumonia and influenza; D: diabetes. bYPLL per 1000 persons, cpercent of the total YPLL.
876
Vol. 8, 1992
Different upper-age limits for YPLL index
In general, the YPLL rates calculated for Catalonia in 1987 were similar to those in Spain for 1978 (5) and 1984 (11) and as compared to those in the United States for t984 (7), despite differences in assessment. Conversely, Catalonia YPLL rates for accidents, suicide/homicide and heart disease are approximately half, one-fourth and one-sixth o f those in the U.S., respectively, while YPLL rates for cancer and liver diseases are 1.3 and 1.9 times higher than those of the U.S. (7). The statistical properties of YPLL are still not known, hence the significance o f differences between groups cannot be calculated. Thus, the usual elaborations based on this index are the YPLL rate, the percent of total YPLL and the empirical comparison of results. However, in the present study the ranking of the YPLL for any given group o f causes suffered very small variation irrespective of the age limit criteria. Similarly, disease-related proportional share of the total YPLL rate was relatively constant; accidents and cardiovascular disease being the most noticeable exceptions. Although the present data describe less than 50,000 cases in a mixed urban and rural area the consistency of the results suggests that extrapolation may be conducted with some confidence within the European Community. In conclusion, in terms of cause-of-death-related ranking of YPLL rates and proportional share of total YPLL, comparability among studies is not affected by the use of 65, 70 nor 75 years as the upper reference age, and, also ought not to affect health-care priorities. Acknowledgements
We thank Dr. Peter R. Turner of SciMed for his valuable help in manuscript preparation. REFERENCES
Benavides EG., Bolumar F. and Peris R. (1989): Quality of Death Certificates in Valencia, Spain Am. J. Public Health 79: 1352-1354.
,
877
2.
Centers for Disease Control (1986): Premature mortality in the United States: public health issues in the use of years of potential life lost - Morbid. Mortl. Wkly. Rep. 35 (Suppl. 2S): 1S-11S.
3. Departament de Sanitat i Seguretat Social (1989): An~tlisi de la mortalitat a Catalunya 1987 - Barcelona: Generalitat de Catalunya. 4.
Garcia L.A. and Cayolla L. (1989): Years of potential life lost: application of an indicator for assessing premature mortality in Spain and Portugal - World Health Stat. Q. 42: 50-56.
5.
Garcia L.A., Nolasco A., Bolumar F. and AlvarezDardet C. (1986): Los afios potenciales de vida perdida: una forma de evaluar las muertes prematuras - Med. Clin. (Barc.) 87: 55:57.
6.
Glaser J.H. (1981): The quality and utility of death certificate data (editorial) - Am. J. Public Health 71: 231-233.
7.
Glass R.I. (1986): New Prospects for Epidemiologic Investigations - Science 234: 951-955.
8. Mahoney M.C., Michalek A.M., Cummings M. et al. (1989): Years of potential life lost among a Native American population - Public Health Rep. 104: 279285. 9. Patella H., Borrel C., Rodriguez C. and Roca J. (1989): Validaci6n de la causa bfisica de defunci6n en Barcelona, 1985 - Med. Clin. (Barc.) 92: 129-134. 10. Romeder J.M. and McWhinnie J.R. (1977): Potential years of life lost between ages 1 and 70: an indicator of premature mortality for health planning - Int. J. Epiderniol. 6: 143-151. 11. Rub M., Borrgzs J.M. and Mingot M. (1990): Mortalidad prematura por cfincer en Espafia - Jano 4: 93-100. 12. World Health Organization (1975): Manual of the international statistical classification of diseases, injuries and causes of death. Based on the recommendations of the Ninth Revision Conference, 1975 - Geneva: World Health Organization.
EUROPEAN JOURNAL
Vol. 8, No. 6
OF EPIDEMIOLOGY BRIEF REPORTS
INFLUENCE OF DIFFERENT UPPER AGE LIMITS ON THE "YEARS OF POTENTIAL LIFE LOST" INDEX A. ORTEGA 1 and
M. PUIG
Basic Medical Sciences Department - School o f Medicine - Universidad de Barcelona San Lorenzo, 21 - 43201-Reus (Spain).
Keywords: Inter-study comparison - Life expectancy - Methodology - Mortality - Years of potential life lost The use of 65, 70 or 75 years as upper age limits for the "Years of Potential Life Lost" index (YPLL) could influence the relative importance assigned to different causes of premature death. Data from a representative year (1987) in Catalonia (Spain), show that health priorities and comparability among studies are not affected by the use of these upper age limits.
The mortality rates currently used in epidemiological studies (crude or age adjusted) provide information on the frequency of the different causes of death but, unless age-specific rates are calculated, give no indication of when these deaths occurred. From the socioeconomic and public health point of view, this information is of importance in assessing life expectancy. To address this problem, an index of lost life-expectancy has been developed that takes into account only those deaths occurring between 1 and 70 years of age; termed the "years of potential life lost" (YPLL) (10). Deaths in the first year of life are not included so as not to give excessive importance to congenital diseases. In 1982, the Centers for Disease Control (USA) began ranking the causes of premature death according to the YPLL. Health priorities ranked by this method were different from the traditional methods. The YPLL index showed that accidents together with cancer and heart disease accounted for the majority of YPLL before the age of 65 (2) and also indicated smoking, alcohol and unintended pregnancies as important causes of avoidable premature mortality and morbidity in the U.S. (7). 1 Corresponding author.
The concept of an YPLL index is widely accepted but the selection of its upper age of reference is debatable. The more common upper limit indicators are 65 (USA) (2, 8) or 70 years of age (Europe) (4, 5). Similarly, three other parameters: 75 years of age, the life expectancy at birth and the life expectancy at the age at which death occurs have also been used. These assessments raise concern regarding the comparability of different studies especially when the influence of this upper limit on the relative importance of the cause-ofdeath is not known. We have studied the effect of different upper limits on the YPLL index and on the relative importance of cause-of-death. Data were collated on deaths occurring in Catalonia, Spain (pop. 5,993,583) in the year 1987. Deaths recorded by age and cause were taken from the official publication of the Department of Health and Social Security of the Autonomous Government of Catalonia (3). The 46,977 death certificates issued (representing > 96% of all deaths in Catalonia in that year) had been coded at a three-digit level, applying the criteria of the International Classification of Diseases-9th revision (12). The YPLL were calculated from grouped data; the intervals used being 1-4, 5-14, 15-24, 25-34, 35-44, 45-54, 55-64 and 65-74 years of age.
875
Ortega A. and Puig M.
Eur. J. Epidemiol.
A uniform distribution_of deaths may be assumed within each of the earlier age intervals, but not necessarily so for the latter two. However, for the present purposes and in lieu of any other weighting procedures available, the assumption may be accepted, albeit none too rigorously, as an initial approach to quantification. Thus, the number of YPLL in a given interval was: (number of deaths) x (upper age limit - middle age of the interval). The upper age-limits were taken as 65, 70 and 75 years. The YPLL rates (per 1000 persons at risk) and the percentage of total YPLL for a given cause-of-death were also calculated. Table 1 shows the YPLL rates for the 12 main causes of death in Catalonia. They account for 75% of the total YPLL. For comparison, their mortality rates are also presented. Cancer was the leading cause of death at all ages in this study and accounted for one third of YPLL. Accidents and cardiovascular diseases were responsible for 150/0 and 11% of YPLL, respectively. Chronic liver diseases contributed approximately 6% of YPLL. The other six causes, in total, represented less than 12%. Cause-of-death ranking remained consistent, irrespective of the upper limit criteria used and despite the increasing YPLL rates. Only congenital abnormalities and homicides lost rank as the reference age increased, while diabetes increased its rank. All three accounted for less than 5% of YPLL and could be considered minor.
In terms of the proportional share of YPLL for the various causes of death, there was an increase for cancer, cardiovascular disease, chronic obstructive pulmonary diseases and diabetes with age. Conversely, the proportional share of YPLL of other causes such as traffic and non-traffic accidents, suicide, homicide and congenital abnormalities was inversely related to the age limit criteria. Verification of the quality of our death certificates was not feasible. However, this aspect has been previously addressed (6). In two Spanish validation studies - one in hospitals in Barcelona (9) and another a population-based study in Valencia (1) - into the underlying cause-of-death, the agreement indices for disease category between the original death certificate and the reference cause-of-death (determined by a panel of experts) were 70 and 80%, respectively well within the usual range of concordance for broad categories of 60 to 90% (1). Another monitor of the quality of the death certificate data is the percent of deaths attributed to a non-specific cause. In the data used, the category "ill-defined conditions" (group 16 of the International Classification of Diseases) had a mortality rate of 7.4 per 100,000 and an YPLL rate of 0.2 per 1000 before the age of 70; less than 1% in both cases. Hence, the validity of our death-certificate data is within acceptable terms.
TABLE 1. - Years of potential life lost rates for several causes-of-death in Catalonia (1987), using different upper reference ages. The crude mortality rates for these causes are also shown in deaths/100,000. Age
65
70
75
Deaths per
Causea
Rank
Rate b
(%)c
Rank
Rate
(%)
Rank
Rate
(%)
C TA HD CLD CVD NTA S COPD CA H D P, I
1 2 3 4 5 6 7 9 8 10 12 11 Other
8.8 3.7 1.6 1.5 1.0 0.9 0.8 0.4 0.5 0.4 0.2 0.2 6.9
(32.8) (13.8) (5.8) (5.4) (3.7) (3.3) (3.0) (1.5) (1.9) (1.4) (0.9) (0.8) (25.6)
1 2 3 4 5 6 7 8 9 10 11 12
13.2 4.3 2.6 2.2 1.7 1.0 1.0 0.7 0.5 0.4 0.4 0.4 9.3
(35.0) (11.4) (6.9) (5.7) (4.5) (2.8) (2.7) (1.9) (1.4) (1.2) (1.1) (1.0) (24.5)
1 2 3 4 5 7 6 8 10 12 9 11
19.1 4.9 4.2 3.1 2.8 1.2 1.2 1.2 0.7 0.6 0.5 0.5 12.7
(36.1) (9.4) (7.9) (5.8) (5.3) (2.3) (2.3) (2.3) (1.4) (1.2) (1.0) (1.0) (24.1)
Total
26.8
37.8
52.8
100,000 1 7 3 5 2 11 9 4 10 12 6 8
203.8 14.7 81.1 24.0 113.0 2.2 6.0 33.9 4.3 1.4 20.6 9.3 268.7
(%) (26) (2) (10) (3) (14) (< 1) (< 1) (4) (< 1) (< 1) (3) (1) (34)
783
aC: cancers; TA: traffic accidents; HD: heart disease; CLD:chronic liver disease and cirrhosis; CVD: cerebrovascular disease; NTA: non-traffic accidents; S: suicide; CA: congenital abnormalities; COPD: chronic obstructive pulmonary disease; H: homicide; P, I: pneumonia and influenza; D: diabetes. bYPLL per 1000 persons, cpercent of the total YPLL.
876
Vol. 8, 1992
Different upper-age limits for YPLL index
In general, the YPLL rates calculated for Catalonia in 1987 were similar to those in Spain for 1978 (5) and 1984 (11) and as compared to those in the United States for t984 (7), despite differences in assessment. Conversely, Catalonia YPLL rates for accidents, suicide/homicide and heart disease are approximately half, one-fourth and one-sixth o f those in the U.S., respectively, while YPLL rates for cancer and liver diseases are 1.3 and 1.9 times higher than those of the U.S. (7). The statistical properties of YPLL are still not known, hence the significance o f differences between groups cannot be calculated. Thus, the usual elaborations based on this index are the YPLL rate, the percent of total YPLL and the empirical comparison of results. However, in the present study the ranking of the YPLL for any given group o f causes suffered very small variation irrespective of the age limit criteria. Similarly, disease-related proportional share of the total YPLL rate was relatively constant; accidents and cardiovascular disease being the most noticeable exceptions. Although the present data describe less than 50,000 cases in a mixed urban and rural area the consistency of the results suggests that extrapolation may be conducted with some confidence within the European Community. In conclusion, in terms of cause-of-death-related ranking of YPLL rates and proportional share of total YPLL, comparability among studies is not affected by the use of 65, 70 nor 75 years as the upper reference age, and, also ought not to affect health-care priorities. Acknowledgements
We thank Dr. Peter R. Turner of SciMed for his valuable help in manuscript preparation. REFERENCES
Benavides EG., Bolumar F. and Peris R. (1989): Quality of Death Certificates in Valencia, Spain Am. J. Public Health 79: 1352-1354.
,
877
2.
Centers for Disease Control (1986): Premature mortality in the United States: public health issues in the use of years of potential life lost - Morbid. Mortl. Wkly. Rep. 35 (Suppl. 2S): 1S-11S.
3. Departament de Sanitat i Seguretat Social (1989): An~tlisi de la mortalitat a Catalunya 1987 - Barcelona: Generalitat de Catalunya. 4.
Garcia L.A. and Cayolla L. (1989): Years of potential life lost: application of an indicator for assessing premature mortality in Spain and Portugal - World Health Stat. Q. 42: 50-56.
5.
Garcia L.A., Nolasco A., Bolumar F. and AlvarezDardet C. (1986): Los afios potenciales de vida perdida: una forma de evaluar las muertes prematuras - Med. Clin. (Barc.) 87: 55:57.
6.
Glaser J.H. (1981): The quality and utility of death certificate data (editorial) - Am. J. Public Health 71: 231-233.
7.
Glass R.I. (1986): New Prospects for Epidemiologic Investigations - Science 234: 951-955.
8. Mahoney M.C., Michalek A.M., Cummings M. et al. (1989): Years of potential life lost among a Native American population - Public Health Rep. 104: 279285. 9. Patella H., Borrel C., Rodriguez C. and Roca J. (1989): Validaci6n de la causa bfisica de defunci6n en Barcelona, 1985 - Med. Clin. (Barc.) 92: 129-134. 10. Romeder J.M. and McWhinnie J.R. (1977): Potential years of life lost between ages 1 and 70: an indicator of premature mortality for health planning - Int. J. Epiderniol. 6: 143-151. 11. Rub M., Borrgzs J.M. and Mingot M. (1990): Mortalidad prematura por cfincer en Espafia - Jano 4: 93-100. 12. World Health Organization (1975): Manual of the international statistical classification of diseases, injuries and causes of death. Based on the recommendations of the Ninth Revision Conference, 1975 - Geneva: World Health Organization.
