Bulletin 10 - Data issues
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Data issues
Deaths data are from the Australian Bureau of Statistics (ABS) mortality
unit record data collection, 1979-93. Population data were obtained from the
ABS. Final estimates have been used for years up to and including 1991; interim
estimates for 1992 and 1993 were based on ABS data as at September 1994.
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)[7] has been used for death registrations beginning in 1979. 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 1993 occurred in an earlier year. A similar
proportion of deaths which occurred in 1993 will not have been registered until
after 1993. 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.
Another approach is to group cases according to the State or Territory in which
the person usually lived. The former method is more appropriate for this
publication, as it tends to emphasise the place where injury occurred (and
might have been prevented). Rates based on place of usual residence were
calculated. Any substantial differences between the two types of rate are noted
in the text.
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 1993. This is the
period during which Australian deaths data have been classified according to
the 9th revision of the International Classification of Diseases (ICD9).[7]
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. For further
information, 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. This may improve comparability.
7. World Health Organization. International classification of diseases (1975
revision). Geneva: WHO, 1977
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