Response rates to Mayi Kuwayu preliminary phase postal distribution
A total of 465 individuals responded to the preliminary Mayi Kuwayu postal distribution. One participant was under the age of 16 years, seven participants were non-Indigenous and one participant completed the survey twice, the duplicate response and non-eligible participants were excluded from the analysis (465-9=456). The overall response rate was 2.3% (n/N=456/20000). Response rates were highest in major cities (2.9%, 95%CI:2.5-3.3) and substantially lower in remote areas (0.8%, 0.6-1.1). There were similar response rates between men and women (male 2.1%, 1.8-2.4, versus female 2.4%, 2.1-2.7). Older age groups were more likely to respond than younger age groups (Table 2).
Table 2. Response rate to the Mayi Kuwayu Study preliminary postal distribution (N=20,000), overall and by gender, age group and remoteness
|
Major cities
|
Regional
|
Remote
|
Total
|
|
n/N
|
response rate (%)
|
95%CI
|
n/N
|
response rate (%)
|
95%CI
|
n/N
|
response rate (%)
|
95%CI
|
n/N
|
response rate (%)
|
95%CI
|
Male
|
|
|
|
|
|
|
|
|
|
|
|
|
16-24
|
8/821
|
1.0
|
0.4–1.9
|
5/1178
|
0.4
|
0.1–1.0
|
2/523
|
0.4
|
<0.1–1.4
|
16/2522
|
0.6
|
0.4–1.0
|
25-34
|
13/857
|
1.5
|
0.8–2.6
|
9/1101
|
0.8
|
0.4–1.5
|
3/512
|
0.6
|
0.1–1.7
|
25/2470
|
1.0
|
0.7–1.5
|
35-49
|
15/708
|
2.1
|
1.2–3.5
|
13/946
|
1.4
|
0.7–2.3
|
1/541
|
0.2
|
<0.1–1.0
|
31/2195
|
1.4
|
1.0–2.0
|
≥50
|
45/756
|
6.0
|
4.4–7.9
|
61/1017
|
6.0
|
4.6–7.6
|
11/547
|
2.0
|
1.0–3.6
|
117/2320
|
5.0
|
4.2–6.0
|
All male
|
84/3142
|
2.7
|
2.1–3.3
|
90/4242
|
2.1
|
1.7–2.6
|
18/2123
|
0.8
|
0.5–1.3
|
195/9507
|
2.1
|
1.8–2.4
|
Female
|
|
|
|
|
|
|
|
|
|
|
|
|
16-24
|
23/928
|
2.5
|
1.6–3.7
|
24/1267
|
1.9
|
1.2–2.8
|
2/553
|
0.4
|
<0.1–1.3
|
49/2748
|
1.8
|
1.3–2.4
|
25-34
|
16/964
|
1.7
|
1.0–2.7
|
15/1148
|
1.3
|
0.7–2.1
|
1/583
|
0.2
|
<0.1–1.0
|
32/2695
|
1.2
|
0.8–1.7
|
35-49
|
21/803
|
2.6
|
1.6–4.0
|
16/1005
|
1.6
|
0.9–2.6
|
2/613
|
0.3
|
<0.1–1.2
|
39/2421
|
1.6
|
1.1–2.2
|
≥50
|
49/886
|
5.5
|
4.1–7.2
|
71/1148
|
6.2
|
4.9–7.7
|
12/595
|
2.0
|
1.0–3.5
|
132/2629
|
5.0
|
4.2–5.9
|
All female
|
109/3581
|
3.0
|
2.5–3.7
|
128/4568
|
2.8
|
2.3–3.3
|
18/2344
|
0.8
|
0.5–1.2
|
255/10493
|
2.4
|
2.1–2.7
|
TOTAL
|
194/6723
|
2.9
|
2.5–3.3
|
222/8810
|
2.5
|
2.2–2.9
|
37/4467
|
0.8
|
0.6–1.1
|
456/20000
|
2.3
|
2.1–2.5
|
*18 participants were missing one or more variable of interest (gender, remoteness, age group) or reported “other” to gender. These missing/other data are not presented in the stratified results but are included in the totals.
The highest response rates were obtained in strata levels aged ≥50 years: males from regional areas 6.0% (4.6-7.6), males from major cities 6.0% (4.4-7.9), females from major cities 5.5% (4.1-7.2), and females from regional areas 6.2% (4.9-7.7) (Table 2). Response rates were ≥2.5% in these jurisdictions: Australian Capital Territory (6.3%,3.1-11.3), New South Wales (3.3%,2.8-3.8), Tasmania (5.0%,3.4-7.1), Victoria (3.6%, 2.7-4.7) and <2% in Queensland (1.7%,1.4-2.9), Western Australia (1.2%,0.8-1.6), Northern Territory (0.6, 0.3-1.1) (Table 3).
Table 3. Response rate to the Mayi Kuwayu Study preliminary postal distribution (N=20,000), by State/Territory
State/Territory
|
Total Responses (n)
|
Total surveys mailed (N)
|
Response rate
|
95%CI
|
ACT
|
10
|
159
|
6.3%
|
3.1–11.3
|
NSW
|
179
|
5415
|
3.3%
|
2.8–3.8
|
NT
|
12
|
1904
|
0.6%
|
0.3–1.1
|
QLD
|
110
|
6318
|
1.7%
|
1.4–2.1
|
SA
|
25
|
1044
|
2.4%
|
1.6–3.5
|
TAS
|
30
|
598
|
5.0%
|
3.4–7.1
|
VIC
|
53
|
1468
|
3.6%
|
2.7–4.7
|
WA
|
37
|
3094
|
1.2%
|
0.8–1.6
|
Total
|
456
|
20000
|
2.3%
|
2.1–2.5
|
Responses over time and by response mode
Most surveys were received by the end of the fourth week (n=390, 85.5%). Sixty-six (14.5%) postal surveys were received between four and 15 weeks (Table 4); however, a large percentage of the paper survey responses (51.6%, n=32/53) received in this period were completed by the respondent within the initial four-week period (Figure 1).
Figure 1. Responses to the Mayi Kuwayu preliminary postal survey distribution by week and response mode
Most participants responded on the paper survey (n=408, 89.5%). Online responses were more common among: younger respondents (15.4% among 16-24 years, 19.0% among 25-34 years, and 17.1% among 35-49 years) compared to respondents ≥50 years (5.2%, p-value for fisher’s exact test<0.01); those with higher education levels (16.9% of university educated) compared to those with lower levels (5.8% of those with year 10 or lower education, p-value 0.04); and, respondents whose first language was an Indigenous language (33.3%) or other (66.6%) compared to those whose first language was English (9.3%, p-value<0.01). Online responses were also more common in participants who responded after 4 weeks (20.7%) compared with those who responded in the first four weeks (9.0%).
Respondent characteristics to the preliminary postal distribution
Respondents included 255 females (55.9%) and 195 males (42.8%), with 194 respondents from major cities (42.5%), 222 respondents from regional areas (48.7%), and 36 respondents from remote areas (8.1%) (Table 4). Among age groups, 251 respondents were aged ≥50 (55.0%), 70 respondents were 35-49 (15.4%), 58 respondents were 25-34 (12.7%), and 65 respondents were 16-24 (14.3%). The survey respondents represented a diversity of financial and education levels. Few respondents spoke an Aboriginal and Torres Strait Islander language as their first language (2.0%, n=9).
Table 4. Characteristics of preliminary Mayi Kuwayu Study postal respondents, overall and by response mode
|
Respondents
|
Response mode
|
|
n
|
% Paper (n/N)
|
% Online (n/N)
|
p-value
|
TOTAL
|
456
|
89.5
|
(408/456)
|
10.5
|
(48/456)
|
--
|
Response received
|
|
|
|
|
|
|
Within 4 weeks
|
390
|
91.0
|
(355/390)
|
9.0
|
(35/390)
|
0.02
|
>4 to 14 weeks
|
66
|
80.3
|
(53/66)
|
19.7
|
(13/66)
|
|
Gender
|
|
|
|
|
|
|
Male
|
195
|
89.7
|
(175/196)
|
10.3
|
(20/196)
|
1.0
|
Female
|
255
|
89.4
|
(228/255)
|
10.6
|
(27/255)
|
|
Unclassifiable
|
6
|
83.3
|
(5/6)
|
16.7
|
(1/6)
|
|
Remoteness
|
|
|
|
|
|
|
Major cities
|
194
|
85.6
|
(166/194)
|
14.4
|
(28/194)
|
0.06
|
Regional
|
222
|
92.8
|
(206/222)
|
7.2
|
(16/222)
|
|
Remote
|
37
|
89.2
|
(33/37)
|
10.8
|
(4/37)
|
|
Unclassifiable
|
3
|
100
|
(3/3)
|
0
|
(0/3)
|
|
Age group
|
|
|
|
|
|
<0.01
|
16-24
|
65
|
84.6
|
(55/65)
|
15.4
|
(10/65)
|
25-34
|
58
|
81.0
|
(47/58)
|
19.0
|
(11/58)
|
|
35-49
|
70
|
82.9
|
(58/70)
|
17.1
|
(12/70)
|
|
≥50
|
251
|
94.8
|
(238/252)
|
5.2
|
(13/252)
|
|
Unclassifiable
|
12
|
83.3
|
(10/12)
|
16.7
|
(2/12)
|
|
Education
|
|
|
|
|
|
|
No school
|
2
|
100
|
(2/2)
|
0
|
(0/2)
|
0.04
|
Up to Year 10
|
189
|
94.2
|
(178/189)
|
5.8
|
(11/189)
|
|
Year 12
|
51
|
94.1
|
(48/51)
|
5.9
|
(3/51)
|
|
Technical or trade
|
126
|
87.3
|
(110/126)
|
12.7
|
(16/126)
|
|
University
|
77
|
83.1
|
(64/77)
|
16.9
|
(13/77)
|
|
Unclassifiable
|
11
|
54.5
|
(6/11)
|
45.5
|
(5/11)
|
|
Financial status
|
|
|
|
|
|
|
Some savings
|
212
|
89.6
|
(190/212)
|
10.4
|
(22/212)
|
0.51
|
Just enough
|
144
|
91.0
|
(131/144)
|
9
|
(13/144)
|
|
No savings
|
60
|
88.3
|
(53/60)
|
11.7
|
(7/60)
|
|
Unsure
|
20
|
100
|
(20/20)
|
0
|
(0/20)
|
|
Unclassified
|
20
|
70.0
|
(14/20)
|
30.0
|
(6/20)
|
|
First language
|
|
|
|
|
|
|
Indigenous language
|
9
|
66.7
|
(6/9)
|
33.3
|
(3/9)
|
<0.01
|
English
|
429
|
90.9
|
(390/430)
|
9.1
|
(39/430)
|
|
Other
|
9
|
33.3
|
(3/9)
|
66.7
|
(6/9)
|
|
Unclassifiable
|
9
|
100.0
|
(9/9)
|
0
|
(0/9)
|
|
*the category unclassifiable was not included in fisher exact test
Reasons for non-completion, ineligibility and return to senders
DHS estimated receiving 500 ‘returns to sender’ (exact number not known), with these surveys destroyed according to a departmental protocol. Sixty-eight calls to the Study helpline were recorded over the period, including from 40 non-Indigenous people who received the survey and were ineligible to participate. Several Indigenous callers who received the survey in the post were concerned about a perceived link between government and the Study, including concerns about data ownership (n=12). Other callers indicated that they could not complete the survey due to disability and/or low literacy level (n=5). All invitations for the caller to complete the survey over the phone were declined. One person who received the postal survey was also contacted in the field recruitment over this period and had not completed the survey due to low literacy.
Determining the sampling frame for the second stage postal distribution
The response rates at four weeks (Supplementary Table 1) were used to determine the distribution for the next stage of postal distribution (180,000 surveys). There was no material difference in response rates at 4 weeks and 15 weeks in each stratum of the sample (Supplementary Table 2). The sampling approach which had been initially proposed for the Study, prior to consideration of these results, planned to over-sample lower responding groups to achieve 500 responses per strata and maximise sample heterogeneity. However, the results from this preliminary phase demonstrated this was not feasible. For example, males 16-24 years living in major cities had a response rate of 0.6%. This equates to receiving one response per 167 surveys posted; to receive 500 returned surveys, an estimated 83,500 surveys would need to be sent, exceeding the number of Indigenous males enrolled in the Medicare database in this stratum (n=12,800 males, major cities, 16-24 years).
The Study team decided that it was a more pragmatic and efficient use of resources to mail the remaining 180,000 surveys to eligible participants in the high response rate groups (Table 5). Compared to sampling all groups proportionately, over-sampling the high response rate groups increased the expected postal survey returns from ~4,000 (2.3% response rate) to ~5,500 (3.1% response rate). Updated Aboriginal and Torres Strait Islander Medicare enrolment figures were provided by DHS on 8 February 2019 to determine the strategy for distributing the remaining 180,000 postal surveys (Table 5).
Table 5. Sample for Mayi Kuwayu Study second phase postal distribution and expected number of surveys returned based on preliminary response rate
|
Major cities
|
Regional
|
Remote
|
TOTAL
|
|
Response rate (%)
|
Surveys sent (N)
|
Estimated returns (n)
|
Response rate (%)
|
Surveys sent (N)
|
Estimated returns (n)
|
Response rate (%)
|
Surveys sent (N)
|
Estimated returns (n)
|
Response rate
(%)
|
Surveys sent (N)
|
Estimated returns (n)
|
Male
|
|
|
|
|
|
|
|
|
|
|
|
|
16-24
|
|
|
|
|
|
|
|
|
|
|
|
|
25-34
|
|
|
|
|
|
|
|
|
|
|
|
|
35-49
|
2.1
|
10660
|
224
|
1.4
|
12176
|
170
|
|
|
|
1.7
|
22836
|
388
|
≥50
|
6.0
|
10351
|
621
|
6.0
|
13409
|
805
|
2.0
|
5044
|
101
|
5.0
|
28804
|
1440
|
Female
|
|
|
|
|
|
|
|
|
|
|
|
|
16-24
|
2.5
|
13950
|
349
|
1.9
|
18020
|
342
|
|
|
|
2.1
|
31970
|
671
|
25-34
|
1.7
|
15640
|
266
|
1.3
|
17605
|
229
|
|
|
|
1.5
|
33245
|
499
|
35-49
|
2.6
|
12660
|
329
|
1.6
|
15293
|
245
|
|
|
|
2.0
|
27953
|
559
|
≥50
|
5.5
|
12943
|
712
|
6.2
|
16031
|
994
|
2.0
|
6122
|
122
|
5.0
|
35096
|
1775
|
TOTAL
|
3.3
|
76204
|
2515
|
3.1
|
92534
|
2869
|
2.0
|
11166
|
223
|
3.1
|
179904
|
5577
|