Subsequently,vital status was monitored by DSP staff through their death registries, with regular cross checks against local residential records kept at the Public Security
Bureau, supplemented annually by active confirmation through street committees
or village administrators. Causes were sought from official death certificates,
supplemented, if necessary, by review of medical records. Underlying causes
were coded according to the 9th International Classification of Diseases (ICD-9)
by DSP staff in Beijing, blind to baseline information. This study analyses deaths
between baseline 1990e91 and 2006