9208.0 - Survey of Motor Vehicle Use, Australia, Oct 2004

ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 19/09/2005

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TECHNICAL NOTE DATA QUALITY

DATA QUALITY

1 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 sampling error or non-sampling error.

SAMPLING ERROR

2 Estimates in this publication are based on information collected for a sample of registered motor vehicles, rather than a full enumeration, and are therefore subject to sampling error. They may differ from the data that would have been produced if the information had been obtained for all registered motor vehicles. Examples of the sampling error for this publication are included in this Technical Note.

3 The sampling error associated with an estimate can be estimated from the sample results. One measure of sampling error is given by the standard error, which indicates the extent to which an estimate might have varied by chance because only a sample of vehicles was included. There are about two chances in three that a sample estimate will differ by less than one standard error from the data that would have been obtained if all vehicles had been included, and about 19 chances in 20 that the difference will be less than two standard errors.

4 Another measure of sampling variability is the relative standard error (RSE) which is obtained by expressing the standard error as a percentage of the estimate to which it refers. The RSE is a useful measure in that it provides an immediate indication of the percentage error likely to have occurred due to sampling. In this publication, estimates that have an estimated relative standard error between 10% and 25% are annotated with the symbol '^' . These estimates should be used with caution as they are subject to sampling variability too high for some purposes. Estimates with an RSE between 25% and 50% are annotated with the symbol '*', indicating that the estimate should be used with caution as it is subject to sampling variability too high for most practical purposes. Estimates with an RSE greater than 50% are annotated with the symbol '**' indicating that the sampling variability causes the estimates to be considered too unreliable for general use.

5 The RSEs relating to 2004 estimates contained in Table 4 of this publication are shown in the following table.

RSE OF MOTOR VEHICLE USE(a), State/territory of registration - Type of vehicle

	Passenger vehicles	Motor cycles	Light commercial vehicles	Rigid trucks	Articulated trucks	Non-freight carrying trucks	Buses	Total
	%	%	%	%	%	%	%	%
Total kilometres travelled

New South Wales	5	20	8	5	5	21	8	4
Victoria	4	26	9	7	5	18	9	3
Queensland	5	17	8	6	6	11	17	4
South Australia	5	22	8	8	6	20	9	4
Western Australia	5	18	8	8	7	17	10	4
Tasmania	5	20	7	7	6	21	9	4
Northern Territory	5	17	10	13	10	18	13	4
Australian Capital Territory	4	21	7	6	6	22	6	3
Australia	2	10	4	3	3	8	5	2
Number of vehicles

New South Wales	2	5	4	2	2	13	8	2
Victoria	1	5	2	3	2	8	6	1
Queensland	3	5	4	2	3	12	5	2
South Australia	2	4	5	2	4	7	6	2
Western Australia	2	3	5	2	2	7	7	1
Tasmania	2	4	2	2	3	6	5	1
Northern Territory	2	8	4	8	3	5	5	2
Australian Capital Territory	2	5	3	2	4	11	6	1
Australia	1	2	2	1	1	4	3	1
Average kilometres travelled

New South Wales	4	20	6	5	4	19	9	3
Victoria	4	26	8	6	4	18	8	3
Queensland	4	17	7	6	5	17	16	3
South Australia	5	22	8	8	5	18	9	4
Western Australia	5	18	9	8	6	15	9	4
Tasmania	5	19	7	7	4	21	8	4
Northern Territory	5	16	10	7	10	19	12	4
Australian Capital Territory	4	20	6	6	5	22	6	3
Australia	2	10	3	3	2	8	5	2

(a) These RSEs relate to the estimates in Table 4.

6 As an example of the use of an RSE, the 2004 estimate for kilometres travelled by all passenger vehicles registered in Australia is 147,728 million kilometres (Table 4 of the publication). The RSE for this estimate is 2%, as shown above. Therefore, the standard error for the 2004 kilometres travelled by passenger vehicles estimate is 2,955 million kilometres. There are about two chances in three that the figure obtained if all vehicles had been included, would have been in the range 144,773 million kilometres to 150,683 million kilometres. There are about 19 chances in 20 that the figure would have been in the range 141,819 million kilometres to 153,637 million kilometres.

7 It is important to note that estimates at more detailed levels than the above are subject to higher RSEs and therefore are less reliable.

8 RSEs for other key variables are shown in the following tables. The RSEs of further detailed variables can be made available on request.

RSE OF FUEL CONSUMPTION(a), Type of fuel - Type of vehicle

		Passenger vehicles	Motor cycles	Light commercial vehicles	Rigid trucks	Articulated trucks	Non-freight carrying trucks	Buses	Total
		%	%	%	%	%	%	%	%
Total fuel consumption

Petrol
	Lead replacement	16	35	23	30	98	45	70	14
	Unleaded	3	12	6	27	100	23	18	2
	Total	3	11	6	22	71	20	17	2
Diesel		17	-	7	4	3	10	5	3
LPG/CNG/dual fuel		13	-	21	44	100	47	23	11
Total		2	11	4	3	3	10	5	2
Average rate of fuel consumption

Petrol
	Lead replacement	8	32	7	7	-	5	15	7
	Unleaded	1	4	2	15	98	6	5	1
	Total	1	4	2	6	46	6	5	1
Diesel		7	-	2	2	1	5	4	3
LPG/CNG/dual fuel		4	-	4	9	98	16	14	3
Total		1	4	1	2	1	5	3	1

- nil or rounded to zero (including null cells)
(a) These RSEs relate to the estimates in Table 5.

RSE of freight vehicles(a), State/territory of operation

	Light commercial vehicles	Rigid trucks	Articulated trucks	Total
	%	%	%	%
Total tonne-kilometres

New South Wales	15	9	5	4
Victoria	21	11	5	5
Queensland	15	12	8	6
South Australia	16	12	9	8
Western Australia	14	12	13	10
Tasmania	17	12	10	8
Northern Territory	19	14	35	33
Australian Capital Territory	16	19	21	13
Australia	8	5	4	3

(a) These RSEs relate to the estimates in Table 13.

9 Summary tables in this publication contain estimates for earlier years. Because of cost and provider load constraints, the SMVU cannot be designed to provide accurate measures of the movements between reference periods. Care should be taken in drawing inferences from changes in data over these years.

10 The standard error for the movement can be calculated using:

where
is an estimate of total of the variable of interest, obtained from the 1st time point
is an estimate of total of the same variable of interest, obtained from the 2nd time point.
is an estimate of movement of the total of the variable of interest from the 1st time point to the 2nd time point ie

11 For total kilometres travelled by type of vehicle from the 2000 to 2004 SMVUs, the standard errors of the movements and the estimates from which they are derived are shown in the following table.

SE OF THE MOVEMENT OF TOTAL KILOMETRES TRAVELLED

	Level estimates				Movement estimates
	2000	RSE (2000)	2004	RSE (2004)	Movement	SE (Movement)(a)
Type of vehicle	mill.	%	mill.	%	mill.	mill.

Passenger vehicles	141 519	3	147 728	2	6 209	5 221
Motor cycles	1 135	8	1 478	10	343	175
Light commercial vehicles	27 829	3	34 007	4	6 178	1 456
Rigid trucks	6 536	4	7 639	3	1 104	346
Articulated trucks	5 578	3	6 013	3	435	217
Non-freight carrying trucks	220	17	221	8	1	41
Buses	1 776	6	1 968	5	191	147
Total	184 593	2	199 055	2	14 462	5 430

(a) Calculated on unrounded RSE estimates.

12 As indicated in the table above, the estimates of movement are subject to significant sampling error and caution should be used in analysing the movements in the estimates. For example, the estimate of movement for passenger vehicles is an increase of 6,209 million kilometres and the standard error is 5,221 million kilometres, which means there are 19 chances in 20 that the true movement estimate is between a decrease of 4,233 million kilometres and an increase of 16,651 million kilometres.

NON-SAMPLING ERROR

13 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 in reporting by providers, 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.

14 Non-sampling error is reduced by the use of pre-advice methodology. This involves vehicle owners receiving early advice about their inclusion in the survey and encourages a higher degree of record keeping. In addition, the reporting of odometer readings taken at the start and end of the survey periods (approximately three months apart) provide reliable estimates of total distance travelled without a recall bias.

Response and non-response

15 An important factor that affects non-sampling error is the response rate achieved. The ABS makes all reasonable efforts to maximise response rates. Where appropriate, mail reminders and telephone follow-up are used to attempt to contact non-responding vehicle owners.

16 Responses were received from 82% of all of the selections for 2004. After removing those vehicles that had been found to be deregistered or out of scope, the live response rate for the 2004 SMVU was 81%.

RESPONSE AND NON-RESPONSE BY CATEGORY

		Percentage of selections 2004

Response received
	Registered vehicle	76
	Unregistered vehicle(a)	6
Non-response
	Untraceable - mailing address unknown	5
	Other(b)	13
Total selections		100

(a) Includes deregistration, out of scope and duplicates.
(b) Includes: responses that were unusable because of unresolved queries or where the vehicle was sold during the reference quarter and the reported data covered less than 14 days; non-response where no listing could be found to enable contact by telephone; and owner contacted by telephone but response still not secured.

17 Live response rates for each state and territory, and for each vehicle type, are shown in the following tables:

LIVE RESPONSE RATES, State/territory

	Response rate
State/territory	%

New South Wales	82
Victoria	82
Queensland	84
South Australia	85
Western Australia	83
Tasmania	82
Northern Territory	72
Australian Capital Territory	74
Australia	81

LIVE RESPONSE RATES, Type of vehicle

	Response rate
Type of vehicle	%

Passenger vehicle	79
Motor cycles	79
Light commercial vehicles	82
Rigid trucks	81
Articulated trucks	85
Non-freight carrying trucks	85
Buses	77
Total	81

18 A large non-response increases the potential magnitude of non-response bias, which occurs if the usage patterns of the non-responding vehicles differ from those of the responding vehicles. For the SMVU, it is assumed that the characteristics of non-responding vehicles including the proportion of deregistered, out of scope and nil use vehicles are the same as for responding vehicles.

Imputation

19 As for previous surveys, the need for imputation of unanswered items on the returned questionnaires remained quite high. Imputation is the process whereby a value is generated for missing data items based on the responses for similar vehicles which were operating for the reference period. Of the questionnaires returned for 2004, 13% needed imputation of one or more items apart from the average rate of fuel consumption. The imputation for average rate of fuel consumption for 2004 was 26%.

Adjustments

20 The SMVU measures 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 2004 SMVU the frame was created on 31 March 2003. 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.

CONTRIBUTION OF ADJUSTMENTS FOR RE-REGISTRATIONS, Australia - SMVU 2004

	Percentage of total kilometres travelled
Type of vehicle	%

Passenger vehicles	1
Motor cycles	6
Light commercial vehicles	2
Rigid trucks	4
Articulated trucks	4
Non-freight carrying trucks	6
Buses	-
Total	2

- nil or rounded to zero (including null cells)

CONTRIBUTION OF NEW VEHICLES REGISTERED AFTER 31 MARCH 2003(a)

	Percentage of total kilometres travelled
Type of vehicle	%

Passenger vehicles	10
Motor cycles	15
Light commercial vehicles	14
Rigid trucks	10
Articulated trucks	17
Non-freight carrying trucks	13
Buses	14
Total	11

(a) Based on data from Sales of New Motor Vehicles, Australia (cat. no. 9314.0).

21 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.

STRATIFICATION CHANGES

22 An investigation into the stratification of the SMVU was conducted in 2003 to determine whether the quality of the SMVU estimates could be improved by using alternate or additional stratification variables or boundaries. The aim of the investigation was to reduce the RSEs of the key data items of total distance travelled and tonne-kilometres travelled, at the state by vehicle type level, while maintaining the existing quarterly sample size of 4,000 vehicles.

23 The investigations showed that by implementing changes to the stratification, a reduction in RSEs for these key data items would be realised. The main changes to the stratification variables were to increase the importance of, and number of, 'vehicle age' cohorts, and to remove 'area of registration'.

24 These changes were implemented for the 2004 SMVU and have resulted in the survey frame being stratified by state of registration, vehicle type, vehicle age and vehicle size.

DISTRIBUTIONS

25 The following tables provide values for total kilometres travelled and total tonne-kilometres travelled for selected percentiles. These percentiles have been calculated from all values reported in each quarter of the reference period. Percentiles provide some indication of the distribution of vehicle use across the survey population. For example, one-fifth of New South Wales passenger vehicles reported a distance travelled of 1,266 kilometres or less for the quarter they were selected in the survey. Note that the minimum value for every combination of state/territory by type of vehicle for both tables is zero.

SELECTED PERCENTILES(a), State/territory of registration - Type of vehicle

		20th Percentile	40th Percentile	50th Percentile (Median)	60th Percentile	80th Percentile	95th Percentile	99th Percentile
Total kilometres travelled

Passenger vehicles
	New South Wales	1 266	2 409	3 030	3 481	5 255	7 605	15 026
	Victoria	1 312	2 353	2 887	3 474	5 156	8 762	13 118
	Queensland	1 460	2 510	2 956	3 817	5 690	8 210	11 113
	South Australia	1 229	2 073	2 549	3 094	5 142	7 215	13 449
	Western Australia	1 101	2 219	2 798	3 534	5 289	8 905	13 881
	Tasmania	811	1 988	2 597	2 992	4 589	7 648	13 453
	Northern Territory	1 227	2 271	2 910	3 415	5 029	9 747	13 507
	Australian Capital Territory	1 718	2 723	3 276	3 725	5 510	8 236	11 098
	Australia	1 274	2 326	2 887	3 477	5 330	8 217	13 118
Motorcycles
	New South Wales	-	332	535	786	1 507	2 924	4 215
	Victoria	-	4	85	324	1 569	3 250	8 026
	Queensland	142	396	590	1 382	2 418	5 184	12 171
	South Australia	-	82	238	356	1 544	3 112	5 873
	Western Australia	-	174	233	474	1 046	2 805	4 077
	Tasmania	-	45	214	358	593	1 626	2 784
	Northern Territory	24	279	361	712	1 168	2 443	2 755
	Australian Capital Territory	36	269	458	684	1 449	3 098	6 605
	Australia	-	183	356	593	1 595	3 623	6 732
Light commercial vehicles
	New South Wales	1 449	2 757	3 194	4 633	6 697	12 513	18 140
	Victoria	1 111	2 741	3 442	4 381	6 993	12 774	21 719
	Queensland	1 337	2 767	3 725	4 660	6 426	11 445	15 669
	South Australia	1 630	2 666	3 838	4 504	6 541	11 210	23 154
	Western Australia	721	2 358	3 256	4 026	6 546	12 777	25 092
	Tasmania	1 042	2 283	2 770	3 594	5 349	9 250	11 919
	Northern Territory	857	2 200	2 715	3 342	5 888	10 394	22 140
	Australia	1 257	2 716	3 469	4 381	6 624	12 277	18 140
Rigid trucks
	New South Wales	1 120	2 731	3 693	4 916	8 475	20 604	35 492
	Victoria	207	1 353	2 730	4 293	8 355	17 673	28 689
	Queensland	853	2 607	3 824	5 403	9 572	20 937	31 588
	South Australia	166	1 422	2 196	3 514	7 758	14 977	27 924
	Western Australia	201	1 504	2 539	3 610	7 043	14 957	30 123
	Tasmania	391	1 691	3 078	4 144	7 559	15 894	25 456
	Northern Territory	258	1 912	2 992	4 073	6 235	12 668	22 951
	Australian Capital Territory	1 203	3 278	5 137	6 705	10 506	19 493	34 179
	Australia	456	2 082	3 208	4 567	8 412	18 782	31 188
Articulated trucks
	New South Wales	3 715	12 666	17 449	22 859	39 473	57 011	94 833
	Victoria	1 356	10 917	15 343	21 912	42 263	59 796	76 914
	Queensland	3 219	12 083	16 538	24 708	47 837	74 285	86 125
	South Australia	4 189	12 813	19 117	24 486	43 127	64 075	94 275
	Western Australia	1 857	7 957	11 938	19 630	32 949	60 150	97 588
	Tasmania	6 295	19 115	22 389	27 465	37 614	54 307	78 544
	Northern Territory	1 533	5 307	8 244	15 309	38 102	81 510	114 334
	Australian Capital Territory	5 195	15 556	27 224	32 192	44 116	62 930	66 853
	Australia	2 668	11 427	16 042	22 824	41 506	63 079	86 125
Non-freight carrying trucks
	New South Wales	499	2 031	2 780	3 346	9 597	16 003	22 690
	Victoria	213	692	914	1 516	5 370	16 357	29 309
	Queensland	123	751	1 898	3 023	5 764	11 747	17 989
	South Australia	319	463	529	887	3 722	7 856	14 596
	Western Australia	1	262	661	1 670	4 288	7 083	12 718
	Tasmania	113	113	113	635	2 261	9 370	10 290
	Northern Territory	47	583	887	1 589	4 921	8 789	24 230
	Australian Capital Territory	339	1 523	2 007	4 650	9 412	22 827	28 841
	Australia	157	596	1 110	2 122	5 388	12 118	19 077
Buses
	New South Wales	2 245	4 207	5 908	8 189	12 488	21 637	27 310
	Victoria	2 155	3 799	5 122	6 131	10 187	16 977	31 041
	Queensland	2 509	4 125	4 959	5 763	13 076	35 118	46 180
	South Australia	2 263	5 525	7 424	9 974	14 859	21 749	34 599
	Western Australia	1 131	3 266	5 094	7 150	13 475	23 809	32 636
	Tasmania	1 990	3 413	4 768	5 467	8 868	16 933	29 640
	Northern Territory	1 878	3 629	4 584	5 705	12 945	26 771	47 764
	Australian Capital Territory	3 046	5 201	6 454	7 580	16 141	24 373	42 936
	Australia	2 245	4 084	5 343	6 834	12 184	24 938	45 254
Total
	New South Wales	1 256	2 367	3 030	3 507	5 443	8 256	16 182
	Victoria	1 136	2 311	2 887	3 499	5 344	9 586	15 941
	Queensland	1 327	2 468	2 977	3 886	5 884	9 185	15 417
	South Australia	1 112	2 074	2 562	3 195	5 242	8 641	16 868
	Western Australia	775	2 068	2 791	3 600	5 430	9 445	20 169
	Tasmania	679	1 930	2 597	3 068	4 727	8 711	17 437
	Northern Territory	1 055	2 167	2 755	3 368	5 156	10 423	20 747
	Australian Capital Territory	1 592	2 658	3 263	3 753	5 533	8 372	12 734
	Australia	1 161	2 295	2 887	3 525	5 521	9 185	15 961

- nil or rounded to zero (including null cells)
(a) Based on distance travelled in a quarter.

SELECTED PERCENTILES(a), State/territory of registration - Type of freight vehicle

		20th Percentile	40th Percentile	50th Percentile (Median)	60th Percentile	80th Percentile	95th Percentile	99th Percentile
Total tonne-kilometres travelled

Light commercial vehicles
	New South Wales	-	5	92	258	1 415	4 579	8 470
	Victoria	-	-	131	350	1 535	4 907	11 956
	Queensland	-	-	12	91	1 085	2 572	7 834
	South Australia	-	-	131	336	1 340	4 066	9 075
	Western Australia	-	-	-	125	1 309	4 653	6 273
	Tasmania	-	-	-	81	678	2 541	5 435
	Northern Territory	-	-	-	85	1 029	4 095	6 773
	Australian Capital Territory	-	53	154	589	1 506	4 106	6 334
	Australia	-	-	50	259	1 276	4 356	8 470
Rigid trucks
	New South Wales	725	2 843	4 778	6 830	19 583	86 872	358 106
	Victoria	96	1 715	2 803	5 244	22 466	84 355	317 826
	Queensland	518	2 685	4 637	7 648	24 691	105 129	341 632
	South Australia	98	1 879	2 847	6 557	22 091	70 816	148 250
	Western Australia	108	2 144	3 642	6 614	18 202	58 436	207 576
	Tasmania	53	1 628	3 002	5 903	17 984	77 484	206 139
	Northern Territory	89	2 029	3 417	5 872	14 093	48 802	90 404
	Australian Capital Territory	710	3 080	4 935	8 540	27 391	127 417	368 250
	Australia	342	2 243	4 013	6 481	21 239	86 872	317 826
Articulated trucks
	New South Wales	32 450	137 262	196 686	275 256	609 471	1 395 962	2 000 527
	Victoria	10 648	105 069	190 971	294 845	819 639	1 633 144	2 085 380
	Queensland	31 043	143 285	207 392	366 900	882 815	1 629 860	4 445 967
	South Australia	37 645	138 119	238 464	376 476	852 093	2 142 308	3 169 246
	Western Australia	10 520	101 775	179 763	254 191	744 069	2 521 360	4 301 740
	Tasmania	71 176	225 660	287 670	363 510	570 230	1 381 423	2 199 431
	Northern Territory	11 947	72 407	130 278	310 080	1 143 695	3 320 713	6 174 040
	Australian Capital Territory	60 425	250 313	406 519	570 587	992 609	1 818 880	2 389 400
	Australia	21 754	127 375	199 458	309 655	777 939	1 634 144	3 155 307

- nil or rounded to zero (including null cells)
(a) Based on distance travelled in a quarter.

26 Users should contact the ABS if they have any queries on the quality and reliability of estimates for particular purposes.