Re: Trends in cause specific mortality across occupations in Japanese men of working age during period of economic stagnation, 1980-2005: retrospective cohort study
This study reported the important findings that suicide mortality of management and professional workers in Japan has increased since the late 1990s, compared with other types of workers. This type of workers has had more stressful incidents and increased pressure at the work place following the economic crisis. The authors focused on the specific problem in Japanese society after the economic recession. The implications they draw from their results are reasonable.
However, there is a crucial problem in the analysis of their study. The occupational mortality was calculated from occupation-specific populations from the national census survey conducted every five year and the occupation of the deceased reported by his/her family in the same census year. The definition of the occupation is “the occupation when the person died”. This study design is thus not “retrospective cohort” but “cross-sectional”. We need, therefore, to be cautious in our interpretation of the results. For example, a person who is diagnosed with cancer often cannot keep the same occupation or position as before their diagnosis. Some patients might change their work; the others might lose their job. In addition, the numerator and denominator of the occupational mortality in this study came from different sources.
In the UK, the Office for National Statistics provides information on the occupation at the last full-time employment for occupational specific mortality statistics. It is possible to get this information by linking the census data to the death certification data. In Japan, theoretically this linkage is feasible, but because of the closed attitudes towards linking national statistics files, we cannot use this type of data.
To monitor the differences in occupational mortality and prevent specific risk from an occupation, we should use more reliable data from the government. We need to argue the importance of linkage study of national statistics files for health policy in Japan. To achieve this, public understanding and support for the efficient use of information from national statistics files are essential.
Competing interests: No competing interests