Epidemiology - Basic Epidemiology
2. Sources of Epidemiological Data
2.1 National Records:
There are certain records relating to individuals that are common to all
countries and these include registration of birth and marriage. Birth records
now include clinical details of the pregnancy and birth including pregnancy complications
and duration, birth weight and birth defects. This can provide invaluable data when establishing
causal links with parents' occupation. Inaccuracies can exist and these are outlined below.
The register of deaths is normally a central record and systems are complete in
Europe, USA, Canada, Australia, Japan and some other industrialised countries.
In many other countries the system is deficient. Registration of death (death certificate)
must be accompanied by a certificate stating the cause(s) of death and signed by a physician;
the cause(s) is entered into the register. This can provide a reasonably accurate measure of serious
illness in the community. Inaccuracies can arise from a number of sources:
- The certifying physician may not have been the person's General Practitioner or attending physician e.g. in hospital
- In a multicausal situation there may be confusion as to what was the ultimate cause
- The certifying physician has to decide what, if any, were underlying causes
The occupation of the individual is specified on the death certificate but this can be of dubious value; it specifies 'last known' occupation but this does not provide information a bout any previous occupations which could be of significance in linking cause of death with occupational exposure. In addition, for people who are retired from work the death certificate may simply record 'retired'; this can be particularly unhelpful as the information would not indicate early retirement due to ill-health and may give no indication even to the last occupation. Consequently the information from death certificates normally needs to be supplemented by information from other sources.
There is now international agreement that the underlying cause of death must be given precedence over the immediate cause. An international numerical coding system for all major diseases is reviewed approximately every ten years and this facilitates international comparisons of mortality data.