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INTRODUCTION 1. ESTIMATED FACTORS FOR TOTAL KILOMETRES TRAVELLED - 12 MONTHS ENDED 30 SEPTEMBER 1996
(b) The estimated factor is statistically significant at the 5% level. The factors shown above were applied to the preliminary estimates of total distance travelled by type of vehicle for the 12 months ended 30 September 1995. Table 2 shows adjusted statistics with the estimated recall bias removed. 2. TOTAL KILOMETRES TRAVELLED BY TYPE OF VEHICLE - 12 MONTHS ENDED 30 SEPTEMBER 1995
(b) The estimated factor is statistically significant at the 5% level. The following table provides estimates of the total distance travelled by type of vehicle in Australia compiled from the 1998 and previous surveys of motor vehicle use. For 1995, both preliminary estimates from the survey and adjusted data to exclude the estimated recall bias are shown. 3. TOTAL KILOMETRES TRAVELLED BY TYPE OF VEHICLE (a)
When the factors are applied to 1995 survey data collected using the old recall methodology, the estimated total distance travelled by all motor vehicles is revised from 166,514 million kilometres to 155,683 million kilometres, a reduction of 7%. This decrease is mainly due to passenger vehicles, where the total distance travelled is revised from 123,691 million kilometres to 113,054 million kilometres. It is not possible to obtain similar adjustments for data prior to 1995. As noted above, it should be recognised that the recall problem which the ABS has attempted to overcome by its new collection methodology for the 1998 survey was inherent in all surveys conducted up to 1995, however there is no reliable measure of how recall biases have varied over time. Taking into account earlier studies, it is reasonable to conclude that estimates of total and average distance travelled for passenger vehicles and total vehicles are also likely to have been overstated in surveys before 1995. Similar generalisations cannot be made for other vehicle types. In particular, for commercial vehicles, record keeping practices appear to have improved over time, with a consequent reduction in recall bias. An historical comparison for total kilometres travelled by passenger vehicles and all vehicles, with the break in series at 1995, is shown in the following graph.
10. The following table provides estimates of the average distances travelled by type of vehicle in Australia. These have been derived by dividing the total distances travelled shown in Table 3 by the number of vehicles estimated to have been registered for use during the relevant year. 4. AVERAGE KILOMETRES TRAVELLED BY TYPE OF VEHICLE (a)
When the factors are applied to 1995 total kilometres data, the estimated average kilometres travelled by all motor vehicles in 1995 falls from 15,200 kilometres to 14,300 kilometres, a reduction of 6 per cent. Again, the decrease is mainly caused by passenger vehicles, where the average kilometres travelled is revised from 14,400 kilometres to 13,100 kilometres. An historical comparison for average kilometres travelled by passenger vehicles and all vehicles, with the break in series at 1995, is shown in the following graph.
Besides average distances based on all registered vehicles referred to above, this publication also contains a number of more detailed average distance travelled tables where estimates relate only to vehicles with a particular use. As stated previously, recall bias adjustment factors are unavailable at the more detailed level. Users are cautioned against applying the same recall bias adjustments to the more detailed tables in order to make historical comparisons. Furthermore, users should be aware of an additional complication affecting the comparability with previous surveys of the averages per vehicle in tables 3 to 12 and 15 to 17. Because vehicle use throughout the year is not constant, having a shorter reporting period of three months means that the proportion of vehicles which report a particular type of usage will be lower than if the reporting period had been 12 months. Therefore, the estimate of the number of vehicles having a particular type of use in the 12 months will be lower and since the denominator is lower, the average distance travelled for vehicles for the 12 months will be slightly higher than under the old method. Document Selection These documents will be presented in a new window.
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