4441.0.55.001 - Voluntary Work, State Tables, 2000  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 20/09/2001   
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TECHNICAL NOTE 1 DATA RELIABILITY


ESTIMATION PROCEDURE

1 Estimates obtained from the survey were derived using a complex ratio estimation procedure which ensures that the survey estimates conform to an independently estimated distribution of the total population by age, sex and area, rather than to the age-sex-area distribution within the sample itself. The estimation procedure is designed to adjust estimates in such a way as to reduce any non-response bias by adjusting the weights of person records in each
age-sex-area cell to compensate for under-enumeration in that cell.

2 Expansion factors or weights are inserted into each person's record to enable the data provided by these persons to be expanded to provide estimates relating to the whole population within the scope of the survey.


RELIABILITY OF ESTIMATES

3 Estimates in this publication are subject to non-sampling and sampling errors.

Non-sampling error

4 Non-sampling error may arise as a result of errors in the reporting, recording or processing of the data and can occur even if there is a complete enumeration of the population. This type of error can be introduced through inadequacies in the questionnaire, non-response, inaccurate reporting by respondents, errors in the application of survey procedures, incorrect recording of answers, and errors in data entry and processing.

5 It is difficult to measure the size of non-sampling errors and the extent of such errors could vary considerably in significance from survey to survey and from question to question. However, every effort is made in the design of the survey and development of survey procedures to minimise the effect of these errors.

Sampling error

6 Sampling error is the error which occurs by chance because the data were obtained from a sample, not the entire population.


STANDARD ERROR OF ESTIMATES

7 One measure of the variability of estimates which occurs as a result of sampling is the standard error (SE). This measures the extent to which an estimate might have varied by chance because only a sample of the population was included. There are about two chances in three (67%) that a survey estimate is within one standard error of the figure that would have been obtained if all persons had been included, and about 19 chances in 20 (95%) that it is within two standard errors. That is, there are 19 chances in 20 that the true estimate is in the range:


8 The SE of an estimate may be obtained from the tables below.


RELATIVE STANDARD ERRORS

9 The SE can also be expressed as a percentage of the estimate and this is known as the relative standard error (RSE). In general, the size of the SE increases as the size of the estimate increases. Conversely, the RSE decreases as the size of the estimate increases. Very small estimates are thus subject to such high RSEs that their value for most practical purposes is unreliable.

10 The RSE is determined by dividing the SE of an estimate SE(x) by the estimate x and expressing it as a percentage. That is:

11 Proportions and percentages formed from the ratio of two estimates are also subject to sampling error. The size of the error depends on the accuracy of both the numerator and the denominator. A formula to approximate the RSE of a proportion is given below. This formula is only valid when x is a subset of y.

12 In the tables in this publication, only estimates with RSEs of 25% or less are considered reliable for most purposes. Estimates with RSEs greater than 25% but less than or equal to 50% are preceded by an asterisk (eg *3.4) to indicate they are subject to high SEs and should be used with caution. Estimates with RSEs of greater than 50% are preceded by a double asterisk (eg **0.3) and are considered too unreliable for general use. They should only be used to aggregate with other estimates to provide derived estimates with RSEs of 25% or less.

13 The following tables provide standard errors and relative standard errors for estimates of persons. Standard errors for estimates of hours are available on request.

STANDARD ERRORS FOR ESTIMATES OF PERSONS
NSW
Vic.
Qld
SA
WA
Tas.
NT
ACT
Australia
Estimate
('000)
no.
no.
no.
no.
no.
no.
no.
no.
no.
5
4,600
4,500
3,600
2,500
2,800
1,400
1,000
1,200
3,400
10
6,800
6,500
5,400
3,700
3,900
2,000
1,300
1,600
5,100
20
9,800
9,300
7,800
5,200
5,600
2,800
1,600
2,200
7,700
50
15,300
14,300
12,100
7,700
8,500
4,000
2,200
3,200
12,500
100
20,800
19,400
16,200
10,100
11,500
5,200
2,600
4,100
17,500
200
27,400
25,700
21,100
12,600
15,300
6,600
3,100
5,100
23,800
500
37,800
35,900
28,400
16,200
21,600
8,700
34,300
800
43,800
42,000
32,500
17,900
25,500
40,500
1,000
46,700
45,100
34,400
18,700
27,500
43,700
1,500
52,100
51,000
37,900
20,100
31,400
49,800
2,000
56,000
55,300
40,400
20,900
34,400
54,200
5,000
68,300
70,000
47,500
69,200

RELATIVE STANDARD ERRORS FOR ESTIMATES OF PERSONS
NSW
Vic.
Qld
SA
WA
Tas.
NT
ACT
Australia
Estimate
('000)
%
%
%
%
%
%
%
%
%
5
91.1
89.1
72.7
50.3
55.0
28.8
19.1
23.7
67.1
10
67.8
65.0
54.1
36.8
39.4
20.1
12.6
16.4
51.5
20
49.1
46.4
39.0
25.9
27.8
13.8
8.1
11.1
38.4
50
30.7
28.7
24.1
15.5
17.0
8.0
4.3
6.4
25.0
100
20.8
19.4
16.2
10.1
11.5
5.2
2.6
4.1
17.5
200
13.7
12.8
10.5
6.3
7.6
3.3
1.5
2.5
11.9
500
7.6
7.2
5.7
3.2
4.3
1.7
6.9
800
5.5
5.3
4.1
2.2
3.2
5.1
1,000
4.7
4.5
3.4
1.9
2.8
4.4
1,500
3.5
3.4
2.5
1.3
2.1
3.3
2,000
2.8
2.8
2.0
1.0
1.7
2.7
5,000
1.4
1.4
1.0
1.4