Commentary: Why the educational effect is so strong in differentials of mortality in Korea?

Mia Son

Kangwon National University, 192–1, Hyoja2-dong, Chuncheon, Kangwon National University, Department of Preventive Medicine, Medical College, Post Code: 200–701. Korea. E-mail: sonmia{at}kangwon.ac.kr

This paper presents educational mortality differentials in Korea. In particular, this study stresses that amongst young people the poorly educated have a higher mortality than the well-educated group.1 This study agrees with findings from previous studies: there is a strong inverse relationship between education and all-cause as well as specific causes of mortality in Korea and education contributes to the wider inequalities in health in Korea.2,3

The authors' question why little research on inequality in health has been carried out in Korea. The authors believe the reason is ‘the ideological climate’, that is, ‘South Korea's regimes have viewed such discussion as an attack upon their political legitimacy.’ However, this situation occurs not only in Korea. In many less developed or rapidly developing countries there has been little such research. One reason for this might be because of the traditional tendency to put biomedicine first in a capitalist society. Capitalist society sees each person as a commodity for labour. The sick body is seen as a machine that needs to be repaired. The work environment and the wider social context are not taken into account. With neo-liberalism, the stress on biomedicine has become even more pronounced. The trend of science is likely to follow the trend of the relationship between labour and capital. Another reason is that the history of social response to the problems of capitalism in Korea is shorter than in many Western countries. Therefore, science still focuses on the individual rather than on social factors in Korea.

Recently several studies on inequalities in health have been done in these less developed or rapidly developing countries. For example, Song and Byeon4 found that among Korean male civil servants, the lowest socioeconomic status (SES) group had significantly higher risk of mortality from most causes compared with the highest SES group, which in rank order were: external causes (relative risk [RR] = 2.26), avoidable causes (RR = 1.65), all-cause (RR = 1.59), and non-avoidable mortality (RR = 1.54). Son2,3 suggested that the association of class—expressed in terms of occupation and educational background—with mortality seems somewhat stronger in Korea than in more developed countries.

This paper suggests that higher mortality rates relate to lower educational attainment for most causes of death.1 This result corresponds to previous research in Korea. Son2 showed that the least-educated group suffer substantially higher mortality than the better educated groups. Mortality ratios for elementary versus university education were 5.11 for men, and 3.42 for women, with intermediately educated groups having mortality between these (Table 1).2 This pattern was present for all specific causes of mortality.2


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Table 1 The standardized mortality ratios (SMR) for all-cause mortality by education, men and women aged 20–64 in Korea

 
The authors in this study showed that the specific diseases which have wider educational inequalities in mortality are tuberculosis, diabetes mellitus, liver disease, and external causes of disease.1 Son2 showed that all disease groups displayed higher standardized mortality ratios (SMR) for lower educational groups. Specific causes of disease, with particularly high SMR among those educated to less than elementary level, were: infectious diseases (tuberculosis), mental disorders due to psychoactive substance use, digestive diseases, most injuries, respiratory diseases (asbestos-related, coal worker's pneumoconiosis, asthma), and musculo-skeletal diseases. For women, the difference in mortality rates between higher and lower educational groups is less notable, although disease patterns are similar. The younger group (aged 20–49) have higher SMR for most specific diseases and injuries, but higher proportional mortality ratio (PMR) for some conditions: infectious diseases (tuberculosis), mental disorders, and respiratory diseases.2 An interesting point from these studies is that communicable diseases, injuries, and musculo-skeletal disease still made a large contribution to class differences in mortality compared with other causes.

The mortality and morbidity ratios by education (less:more) were considerably higher in Korean men than in Europe or the USA. The ratios by education in women were somewhat lower than among men in Korea, but still (for mortality) above equivalent ratios in the UK and the USA, which were also lower than the ratios in those countries for men.2,3 Another interesting point from the study of inequality in mortality in the Korean population, not included in this study, was the significant interactions between occupational class and education (for men and women: P < 0.001).2 In fact, patterns of mortality by education were remarkably similar amongst non-manual and manual workers. There were also significant interactions of occupational class and education with age, but the size of these effects were small. The associations of occupational class and education with mortality were somewhat stronger in the younger than the older group.2,3

Why is the educational effect so marked in Korea? Why in Korea is the educational effect so strong in the younger age group? Perhaps it is because education has a stronger effect on occupational position and material well-being in Korea. Since the Korean War, the Korean people have survived economically in the exploitative climate of domestic capitalism and imperialism through major investment in education.4 Education is an important qualification and instrument for obtaining a better job in Korea.4 As skills obtained from education or training enable the specialization of labour-power, gaining a better education can be the main reason for obtaining better employment and occupation.2

In summary, several studies from Korea show that a strong inverse relationship may have a different meaning from that in more developed countries. In particular, the strong effect of education on mortality in the younger group suggests that the effect of capitalism has been very strong in the young workers in the rapidly developing countries like Korea. Another important point from the Korean studies is that education cannot be considered independently, as education and occupation are closely linked.

As for study limitations, the authors recognize the numerator-denominator bias in their study. Misclassification of education is likely in the Census and particularly in death records in Korea.3,6 This study has a limitation in that there may be differential and non-differential misclassification in the numerators from the national death data and denominators from the Census. As for the validity of the educational variable in national death data, Kong et al.7 showed that concordance amounts to 79% between the record in the national death data and an interview survey. Another study on the comparison of the educational variable in workplace injury data and national death data showed that the broader categories for beyond/below university level seem to exhibit reasonable agreement (Kappa index: 0.50, agreement: 86.93%), but the more detailed categorization leads to poor agreement for education.6 The educational variable may be poorly matched between the two surveys partly because of inaccurate recording of educational achievement, with some people indicating higher educational levels than actually attained. This comparison study suggests that random errors, misclassification, as well as systemic errors are all likely. There might thus be considerable bias due to the misclassification of the educational variable in the numerators from the national death data and denominators from the Census. This may cause non-differential and differential bias and there may be some consequent overestimation of the educational effect on mortality. The size and seriousness of any numerator-denominator bias remains to be studied in Korea.6

To overcome the limitation of aggregate data from Census and death certificate data, a cohort study is needed. There may be a possibility of linking death and population through the utilization of social security numbers in Korea. We also need a combined study using several socioeconomic variables to understand the full scope of socioeconomic differentiation.


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1 Khang Y-H, Lynch JW, Kaplan GA. Health inequalities in Korea: age- and sex-specific educational differences in the 10 leading causes of death. Int J Epidemiol 2004;33:299–308.[CrossRef][ISI][Medline]

2 Son M. Occupational Class and Health: The Differentials in Mortality, Morbidity and Workplace Injury Rates by Occupation, Education, Income and Working Conditions in Korea. PhD thesis in the faculty of Medicine of the University of London, London School of Hygiene & Tropical Medicine, London: 2001.

3 Son M, Armstrong B, Choi J-M, Yoon T-Y. The relationship of occupational class and education with mortality in Korea. J Epidemiol Community Health 2002;56:798–99.[Free Full Text]

4 Song YM, Byeon JJ. Excess mortality from avoidable and non-avoidable causes in men of low socioeconomic status: a prospective study in Korea. J Epidemiol Community Health 2000; 54:166–72.[Abstract/Free Full Text]

5 Heide H. The subjective condition for establishment of capitalism in Korea. In: Kim S (ed.). Future in the workplace. Korean Institute for Labour Studies & Policy 2000;59:129–67. Seoul: Future in the Workplace Press, 2000.

6 Son M. A comparison of occupation, education, and cause of death from national death certificates and deaths data due to workplace injuries from WELCO in Korea. J Korean Epidemiol 2002;23:44–51.

7 Kong S-K, Lim J-K, Kim M-K. Mortality and Causes of Death. Seoul: Korea Institute for Population and Health, 1980.