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9208.0 - Survey of Motor Vehicle Use, Australia, Oct 2004  
Previous 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 Equation: EQ5

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.

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