Survey of Motor Vehicle Use, Australia methodology

1 This publication presents estimates of motor vehicle use in Australia between 1 July 2017 and 30 June 2018. Estimates are compiled from the ABS' Survey of Motor Vehicle Use (SMVU). This survey included a sample of vehicles registered in Australia during this period.

2 The scope of the survey comprised all vehicles registered with a motor vehicle authority for road use during the 12 months ended 30 June 2018. Not included were caravans, trailers, tractors, plant and equipment, vehicles belonging to the defence services and vehicles with diplomatic or consular plates. Where they were registered as such, vintage and veteran cars were also excluded from the survey. Unregistered vehicles were out of scope.

3 Vehicles were identified using information obtained from state and territory motor vehicle registration authorities as part of the annual ABS Motor Vehicle Census (see Motor Vehicle Census, Australia (cat. no. 9309.0)). The Motor Vehicle Census (MVC) provides a snapshot of registered vehicles at 31 January each year. There were 19 million vehicles identified from the MVC at 31 January 2017. These vehicles provided the population of vehicles, or survey frame, for the 2018 SMVU.

4 For the 2018 SMVU, a sample of 16,000 vehicles was selected for inclusion in the survey. The survey sample consisted of passenger vehicles (17.42%), motor cycles (5.27%), freight vehicles (65.73%), buses (8.34%) and non-freight carrying vehicles (3.24%). The sample size was chosen to give a suitable level of reliability for estimates of total distance travelled and tonne-kilometres travelled for each state/territory of registration by type of vehicle category over the survey period.

5 Vehicles were selected for one of three data collection periods, each 4 months in duration.

6 Owners of vehicles selected in the survey were asked to complete two questionnaires, either paper or web, tailored to their vehicle type. The first, at the beginning of the survey period, asked for selected vehicle characteristics and the vehicle odometer reading. Owners were also advised they would receive a follow up questionnaire at the end of the period, with examples of the main items included. The second questionnaire requested details about the use of the vehicle over the four month period and a second odometer reading.

7 When questionnaires were returned to the ABS they were checked for completeness and accuracy and, where possible, follow-up contact was made with owners to resolve reporting problems. Where contact with owners could not be made, missing items on incomplete questionnaires were filled by using data from like vehicles for which data were obtained.

8 Where the selected vehicle owner had not owned the vehicle for the whole four month survey period, the usage details provided for the period of ownership were adjusted to give a four-month equivalent. Where the vehicle was deregistered during the four month survey period, only usage up to the date of deregistration was included.

9 In addition, adjustments were made in the estimation process to account for the use of new motor vehicles registered after the survey population was identified, as well as the re-registration of other vehicles during this time. More information about these adjustments is provided in paragraph 27 of the Technical Note.

10 Estimates from information reported in each four month collection period were produced and these were then aggregated into annual estimates relating to the use of vehicles during the period 1 July 2017 and 30 June 2018.

11 When interpreting the results of a survey it is important to take into account factors that may affect the reliability of estimates. Such factors can be classified as either survey methodology, sampling error or non-sampling error. Information on these factors is provided in the Technical Note.

12 The 2018 survey instrument included a change to the question design and wording relating to fuel consumption over the four month collection period. The question related to fuel consumption has historically been difficult for respondents to answer. 

13 The change removed the burden of multiple reporting options. The previous question asked respondents to report, or calculate and record their average rate of fuel consumption (litres per 100 kilometres) over the four month reporting period. This was replaced with a simpler question asking for the total amount of fuel used over the four month collection period. To assist respondent recall, an optional log sheet was also provided to record the amount of fuel purchased over the collection period. 

14 As a result of the change to the fuel consumption question, care should be taken when interpreting the estimates for total fuel consumption and average rate of fuel consumption.

15 Survey estimates of the numbers of vehicles, by vehicle type for SMVU are not fully comparable with ABS Motor Vehicle Census data (see Motor Vehicle Census, Australia (cat. no. 9309.0)). The main differences are:

• Survey estimates of the numbers of vehicles relate to the average number of vehicles registered for road use during the period 1 July 2017 to 30 June 2018, not to the number of vehicles registered at a specific date, as is the case for the Motor Vehicle Census.
• Characteristics of the vehicle reported in the survey information may differ from those recorded by the motor vehicle registries.
   

16 Most tables in this publication include statistics presented as averages. The denominator used in calculating these averages varies depending on the characteristics of interest. The method of calculating each average is noted in the table where it is presented. As the denominators used to calculate each average are different it should be noted that the averages along a table row cannot be used to derive the total column entry for that row.

17 This publication includes estimates of vehicle use for earlier years. However, it should be noted the survey was designed to produce reliable estimates of key data items for a point in time, not for year-to-year changes. Estimates of movement over time are subject to high sampling error and care should be taken in drawing inferences from these comparisons. See paragraphs 9-13 of the Technical Note for further information.

18 Users may also wish to refer to the following publications and products which contain information relating to motor vehicles in Australia:

Microdata: Motor Vehicle Use, Australia, 2018 (cat. no. 9208.0.55.008)
Motor Vehicle Census, Australia (cat. no. 9309.0)
Sales of New Motor Vehicles, Australia (cat. no. 9314.0)
Road Freight Movements, Australia (cat. no. 9223.0)

19 As well as the statistics included in this publication, the ABS has other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070.

1 When interpreting the results of a survey it is important to take into account factors that may affect the reliability of estimates. The survey procedures as well as sampling and non-sampling errors should be considered. Examination of the following quality indicators will assist users in determining fitness for purpose of estimates produced from the Survey of Motor Vehicle Use (SMVU).

14 Non-sampling error covers the range of errors that are not caused by sampling and can occur in any statistical collection whether it is based on full enumeration or a sample. For example, non-sampling error can occur because of non-response to the statistical collection, errors or omissions in reporting, definition or classification difficulties, errors in transcribing and processing data and under-coverage of the frame from which the sample was selected. If these errors are systematic (not random) then the survey results will be distorted in one direction and therefore will be unrepresentative of the target population. Systematic errors result in bias.

15 A number of indicators of possible non-sampling error are outlined below.

16 Imputation is the process whereby a value is generated for missing data. Data may be missing for a particular data item (partial imputation), or for a unit which has not responded to the questionnaire (full imputation). For the SMVU, imputed values are based on responses for similar vehicles which were operating for the reference period.

17 Imputation introduces non-sampling error, and the contribution to estimates from imputed data provides one measure of the reliability of the estimates. As for previous surveys, the need for imputation of unanswered items on the returned questionnaires remained quite high. The tables below show the percentage contribution to the estimates from both partial and full imputation.

18 An important factor that affects non-sampling error is the response rate. The ABS makes all reasonable efforts to maximise response rates. For the SMVU, mail reminders and telephone follow-up were used to attempt to contact non-responding vehicle owners. Usable responses were received from 79% of all of the selections for 2018, comprised of 77% from registered vehicles and 3% from unregistered vehicles, out of scope and duplicates.

19 After removing those vehicles that had been found to be deregistered or out of scope, the response rate for the 2018 SMVU was 79%.

20 Response rates for each State and Territory, and for each vehicle type, are shown in the following tables:

21 For the SMVU, it is assumed that the characteristics of non-responding vehicles are the same as for like responding vehicles. Non-response has the potential to cause non-response bias, which occurs if the usage patterns of the non-responding vehicles differ from those of the responding vehicles. For example, the lowest response rate achieved by vehicle type was for light commercial vehicles (76%). This could result in the estimates for light commercial vehicles being of a lower quality than other vehicle types.

22 A population or survey frame of 19 million vehicles was identified on 31 January 2017 using information obtained from the state and territory motor vehicle registration authorities, as part of the annual ABS Motor Vehicle Census (MVC) (cat. no. 9309.0).

23 The reliability of this frame in providing an accurate number of vehicles in scope of the survey is indicated by the number of duplicate vehicle registrations, vehicle de-registrations prior to frame extract, and out-of-scope vehicles identified. For 2018, approximately 0.5% of the total frame were identified as such. This indicates the frame was reliable in terms of providing an accurate number of registered vehicles in Australia.

24 Another indicator of frame quality is the number of units identified as in scope with different characteristics compared to what was recorded on the frame. For the SMVU, this can arise when respondents indicate an alteration has been made to the vehicle body, resulting in a different body type to that recorded on the frame. These changes can happen during the time-lag between finalising the frame and collection of SMVU data (between 5 and 17 months). Vehicle classification anomalies can also result from data supplied by state and territory vehicle registration authorities.

25 An assessment of vehicle classification anomalies from 2018 data shows that while there was no bias towards specific states or territories, there were marked discrepancies for some vehicle types. For vehicles on the frame that were listed as non-freight carrying trucks, 17.2% were found to be other vehicle types and 14.2% of vehicles listed as buses were found to be other vehicle types. This issue was not significant for other vehicle types on the frame.

26 The survey is comprised of three independent samples, with a different sample used for each four month period in the overall 12 month survey period. Estimates from each of these samples are aggregated and adjusted for new motor vehicles and re-registrations of vehicles to produce an annual estimate.

27 The SMVU aims to measure the use of all vehicles registered during the reference year. Because selections are taken from vehicles registered some time before the beginning of each collection period, adjustments are made to account for the change in size of the registered motor vehicle fleet since the population frame was created. For the 2018 SMVU, the frame was created on 31 January 2017. These adjustments involved two categories:

• re-registrations - older vehicles that are returning to the registered vehicle fleet after a period of de-registration, and
• new motor vehicles - vehicles which have not been previously registered.
   

28 These activities occur continuously and the adjustments are made to account for the registrations that are estimated to have been added to or removed from the registered vehicle fleet between the population frame date and the end of the reference period. The adjustment process also accounts for de-registrations. This means it is possible for the re-registration factor to be negative.

29 Some providers may report nil use for the 4 month reference period in which they were selected. Nil use vehicles are registered vehicles that report no travel during that specific reference period. Nil use vehicles are included in the survey as their reported nil use is representative of other vehicles in the population. Vehicles may have nil use due to factors such as seasonal usage, mechanical faults or economic conditions. Where a provider gives a nil use response, a follow-up phone call is used to check the veracity of the response.