Bulletin 13 - Data issues
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Data issues
Deaths data are from the Australian Bureau of Statistics (ABS) mortality unit
record data collection, 1979-94. Population data were obtained from the ABS.
The cause of each death registered in Australia is classified by the ABS
according to the International Classification of Diseases (ICD). The 9th
revision (ICD9) has been used for death registrations beginning in 1979 [2].
All deaths given an ICD9 "External Cause" code by the ABS are
included in this Bulletin.
Data are presented according to the year in which deaths were registered. Nine
percent of deaths registered in 1994 occurred in an earlier year. A similar
proportion of deaths which occurred in 1994 will not have been registered until
after 1994. Information on these cases is not yet available. State-specific
data are presented on the basis of the state or territory in which death was
registered. This is normally the one in which death occurred.
Most all-ages rates have been adjusted to overcome the effect of differences in
the proportions of people of different ages (and different injury risks) in the
populations that are compared. Direct standardisation was employed, taking the
Australian population in 1991 as the standard.
All deaths are registered, so sampling errors do not apply to these data.
However, the time periods used to group the cases (ie. calendar years) are
arbitrary. Use of another period (eg. July to June) can result in different
rates. Where case numbers are small, the effect of chance variation on rates
can be large. Confidence intervals (95%, based on a Poisson assumption about
the number of cases in a time period) have been placed around rates as a guide
to the size of this variation. Chance variation alone would be expected to lead
to a rate outside the interval only once out of 20 occasions. An extreme rate
in a single period of enumeration should not be ignored simply because of a
wide confidence interval - a time series may show such a rate to be part of a
more significant pattern.
Time trends have been presented for the period 1979 to 1994. This is the period
during which Australian deaths data have been classified according to the 9th
revision of the International Classification of Diseases (ICD9).
NISU statistical publications make use of standard aggregations of the ICD9
external cause (E-code) classification. The E-code equivalents of most groups
presented in this Bulletin are noted in the text. In 1992, a uniform
supplementary classification was, for the first time, applied to drowning
deaths in all states and territories. This supplementary classification allows
for the identification of more detailed groups of drowning cases than is
possible under the ICD9 classification, eg. drowning in domestic swimming
pools. The reliability of the supplementary classification for drowning is
unknown. For further information, refer to NISU's WWW site
(http://www.nisu.flinders.edu.au) or contact NISU.
The chief question concerns the reliability of information about type of injury
death. This depends principally on the information available in coroner's
records, and on the reliability of the application of ICD9 E-codes, generally
based on that information. Little empirical information is available. There is
considerable potential for factors to do with information recording or coding
to affect data in different ways for different states and territories. Hence,
apparent differences between jurisdictions should be interpreted with caution.
Beginning with 1993 registrations, coding has been centralised at the Brisbane
office of the ABS.
2. World Health Organization. International classification of diseases (1975
revision). Geneva: WHO, 1977.
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