© Borgis - New Medicine 4/2006, s. 97-101
*Irena Maniecka-Bryła1, Ireneusz Kuropka2
Increase in life expectancy as an expression of favourable changes in mortality*
1Department of Social and Preventive Medicine, Medical University in Łódź
Head of Department: Prof. Wojciech Drygas, M.D., Ph.D.
2Department of Economic Forecasts and Analyses, Academy of Economics in Wrocław
Head of Department: Prof. Paweł Dittmann, Ph.D
Introduction. This paper aims to evaluate the changes in overall mortality and life expectancy of Łódź inhabitants, with an emphasis on the 65-74 age group, which occurred during 11 years of the socio-economic transformation and demographic transition in Poland.
Material and methods. Our study is based on secondary sources. We make use of complete mortality databases of the Łódź population, the WHO database, data tables of the Central Statistical Office stored in an archive, and materials of the Regional Public Health Centre in Łódź. Our analysis concerns two years: 1991 and 2002. We applied the following statistical methods: indices of proportion, intensity and dynamics, direct standardisation, u-test for two frequencies. In order to calculate life expectancies in the investigated age groups in Łódź in 1991 and 2002, we used the method proposed by Greville.
Results. Favourable changes in the life expectancy profile for every year in the 65-74 age group among both genders in Łódź were observed. At the same time, the differential of male and female life expectancies diminished in 2002 in comparison with 1991. It turned out that the length of life of a male Łódź inhabitant aged 65 was shorter by 0.77 year in 1991 than that of a male Pole in the same age category, whereas it was 1.13 year for a female inhabitant compared to a female Pole. The elimination of deaths due to CVD would have resulted in a gain of 9.92 years in e(65) in 1991 among males and 10.33 years among females, whereas in 2002 it would have been 4.48 and 4.20 years respectively.
Conclusions. Positive changes in mortality were confirmed. Mortality is considered to be an important element of the health situation of the "young old” (i.e. aged 65-74) population in Łódź in the period under study, which brought about an increase in survival probability. The magnitude of the gain in life expectancy, assuming a total elimination of CVD mortality, justifies our opinion that these diseases constitute the most important health problem.
This paper aims to evaluate the changes in overall mortality and life expectancy of Łódź inhabitants, with an emphasis on the 65-74 age group, which occurred during 11 years of the socio-economic transformation and demographic transition in Poland.
We chose the year 1991 as the reference point of our considerations due to the worst epidemiological situation, in particular as far as the most important health problem, i.e. cardiovascular diseases (CVD), is concerned. The health situation of the population considered to constitute the young old population in 1991 was compared to that in 2002, when clearly positive changes of health phenomena examined by us had continued for several years. In the period under study, apart from the socio-economic and epidemiological transitions, various demographic changes occurred, the result of which was, inter alia, the progressive process of our city population´s ageing [1, 2]. It is worth noting that in this period, the number of Łódź inhabitants decreased by 52,239 people, i.e. by 6.26%, and reached 782,540 on 30 June 2002. The number of inhabitants aged 65 and over increased by 13,693, i.e. by 11.73%, and reached 130,409 in 2002. People aged 65-74 constituted the biggest group of the population aged 65 and over – 64.30% in 1991 and 59.15% in 2002, i.e. respectively 75,401 and 77,131 people. This means that in the period under study, every tenth Łódź inhabitant belonged to this age group . Because of the unfavourable demographic and health situation of Łódź inhabitants compared to the entire country, this paper provides numerous references to Poland as a whole, particularly while evaluating the most important mortality elements.
Material and methods
Our study is based on secondary sources. We make use of complete mortality databases of the Łódź population, the WHO database, data tables of the Central Statistical Office stored in an archive, and materials of the Regional Public Health Centre in Łódź. Our analysis concerns two years: 1991 and 2002. We applied the following statistical methods: indices of proportion, intensity and dynamics, direct standardisation, u-test for two frequencies . In order to calculate life expectancies in the investigated age groups in Łódź in 1991 and 2002, we used the method proposed by Greville. Since this method has rarely been used in medical papers, it seems desirable to describe it in general terms.
Life tables are a collection of biometric functions showing the order of ageing of a hypothetical generation. The basic parameter of life tables – the probability of death – is calculated on the basis of real partial mortality indices occurring in a given period. The other variables are derived from the calculated death probabilities for a given age [5, 6, 7].
Therefore, life expectancy at x measures the life potential of a person of a given age. Life expectancy at birth describes in a synthetic way mortality conditions concerning a population in a given period. Despite being a hypothetical value, it is the most common measure used to evaluate this kind of situation. This parameter reflects the impact of various factors shaping the mortality of a population and it depends on the conditions of life. It is affected by many social, economic and cultural factors [8, 9, 10, 11, 12]. That is why E. Rosset [13, 14] considered life expectancy to be "a barometer of social progress”.
The method of calculating life table parameters based on the assumption of an even distribution of deaths is called traditional and it is seldom used in practice. The reason is above all the changeable and uneven distribution of infant deaths. To calculate the death probabilities, a modification of the formula proposed by Greville, allowing a reduction of this error , was used.
Due to the limits of this paper, we will present only the extension of life expectancy for the 65-74 age group in the period 1991-2002 as well as an assessment of gains in this important health situation indicator on the assumption of a total elimination of CVD mortality.
Table 1 shows the dynamics of overall mortality in Łódź compared to Poland in the period under study. Data included in this table indicate that overall mortality indices both in Łódź and in Poland declined, but they were always significantly higher in Łódź than in Poland. The dynamics of the decline of the overall mortality rate in Łódź was similar to that in Poland, although it continues to be lower than in Łódź (by 3.6% in 2002).
Table 1. The dynamics of overall mortality in Łódź and in Poland in the period 1991-2002.
|rate per 1000 population ||1991=100||rate per 1000 population||1991=100|
Source: own research on the basis of data provided by the Regional Statistical Office in Łódź and http://www.3.who.int/whosis/mort/table1_process.cfn.
Due to the more advanced ageing process in Łódź than in the entire Polish population, so as to assess the overall mortality rate differentials which result from the health situation and not from the demographic situation, direct standardisation was carried out. This enabled us to make the compared indices independent of population age structure differences. With the aid of standardisation, one may establish how many deaths would have occurred in the analysed population (Łódź in this case) if the age structure had been identical to that of a standard population. We took the structure of the Polish population as a standard. Our calculated standardised rates are much lower than the real ones among males, females and in the entire population. The differential between Łódź and Poland in 1991 fell to 1.2% in the total population and to 0.8% in 2002. However, overall mortality rates in Łódź continue to be statistically significantly higher than in Poland at the significance level of p<0.001, which was confirmed by a u-test (Figs. 1 and 2). This is evidence for our thesis that the health situation of Łódź inhabitants is worse than that of Poles, because mortality rates are its most negative measures. Comparing overall mortality rates in Łódź and in Poland in the years under study, we found that they were statistically significantly (p <0.001) higher in Łódź both among males and females. In the period under study, there was a favourable reduction of these rates both in the Łódź population and in that of Poland. The standardised overall mortality rate in Łódź fell by 12.8% (14.7% among males and 11.5% among females). In Poland, this decline was smaller and it amounted to: 10.5%, 11.1% and 10.5% respectively. It is worth noting that the dynamics of decline of overall mortality rates in the population aged 65-74 was higher than the dynamics of decline of these rates for the entire population. This applies to both males and females. In Łódź, this rate fell by 21.2% (18.1% among males and 22.6% among females), whereas in Poland it fell by 17.3%, 15.1% and 22.0% respectively.
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