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Warning over mortality rates; Yousay IN YOUR OPINION...

AS Head of Health Analysis at the Office for National Statistics (ONS), I would like to comment on the article "Caution urged over village's high death rate" (January 6), where the mortality rates in small areas in England and Wales were compared to the national mortality rates of Rwanda and Botswana.

These mortality rates, published separately by ONS and the World Health Organisation (WHO), are not comparable because of differences in the methods of calculation used by the two organisations.

Both ONS and the WHO publish mortality rates using a statistical method called indirect standardisation, which allows meaningful comparison of mortality rates between areas by accounting for differences in the age structure of their populations.

The result of the calculation depends on the standard population used.

In England and Wales, as throughout Europe, the standard used is designed to be appropriate for relatively old populations. The WHO, however, publishes its statistics using a standard designed for populations with a much younger age profile.

This produces different results from the "same" calculation. For example, the mortality rate in Bryncethin ward, Bridgend, which was correctly quoted as 1,499 per 100,000 based on ONS's standard method, would be only 1,048 per 100,000 using WHO's standard population.

Another difficulty for this comparison is that the UK has a long established and reliable death registration system which achieves complete coverage of all deaths. In countries such as Rwanda and Botswana, the recording of deaths is known to be very incomplete, so that mortality rates for these countries have to be estimated by WHO from limited information.

Finally, I want to emphasise that mortality rates for small areas are necessarily uncertain and volatile. This is why ONS does not routinely publish mortality statistics for areas smaller than whole local authority districts. For example, the ward of Bryncethin has a population of just 1,276 people.

Although the data and methods used by ONS are reliable in themselves, the number of deaths among such a small population can vary widely by chance, and the figures may also be affected by the presence in the area of a nursing home or hospice.

Consequently, the table you quoted showed confidence intervals for each mortality rate: these are a measure of the statistical precision of an estimate and show the range of uncertainty around the given figure.

* Myer Glickman Head of Health Analysis, Health and Life Events Division, Office for National Statistics
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Title Annotation:Letters
Publication:South Wales Echo (Cardiff, Wales)
Date:Jan 12, 2012
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