Data user guide

The Longitudinal Study of Australian Children: An Australian Government Initiative
Data User Guide – December 2018

11. Survey methodology

LSAC employs a cross-sequential design that follows two cohorts of children, initially aged 0-1 years (B cohort) and 4-5 years (K cohort) in 2004.

Families are visited by interviewers every two years to collect data for the main waves of the study. In the 'between' years, a mailout survey was conducted at Waves 1.5, 2.5 and 3.5 to help maintain contact with families and obtain some additional information. At Waves 4.5 and 5.5, a web form was used primarily to update contact details.

The key features of the initial sample design and methodology for each wave are included in this section. A full description of the sample design is given in LSAC Technical Paper No. 1 Sample design [PDF 627 KB] and details of the weighting and non-response analysis are given in subsequent technical papers. Get more information about the technical papers.

11.1 Sample design

A two-stage clustered sample design was employed, first selecting postcodes then children, with the clustered design allowing analysis of children within communities and producing cost savings for interviews.

Stratification was used to ensure proportional geographic representation for states/territories and capital city statistical division/rest of state areas. The sample was stratified by state, capital city statistical division/balance of state and two strata based on the size of the target population in the postcode.

Postcodes were selected with probability proportional to size selection where possible, and with equal probability for small population postcodes. Children from both cohorts were selected from the same 311 postcodes. Some remote postcodes were excluded from the design, and the population estimates were adjusted accordingly.

Children were selected with approximately equal chance of selection for each child (about one in 25).

Apart from some remote areas, the sample was selected to be representative of all Australian children (citizens and permanent residents) in each of two selected age cohorts:

  • children born March 2003-February 2004 (B cohort)
  • children born March 1999-February 2000 (K cohort).

11.1.1 Sample selection and recruitment

The sample was selected from Medicare Australia's enrolment database. Within the selected postcodes, the population was ordered by date of birth and then a random start and skip applied to select the children. The actual number of children selected depended on which stratum the postcode was in but for most postcodes the aim was to recruit about 20 children per cohort per postcode.

The selection of children and corresponding Wave 1 fieldwork occurred in four phases, partly to reduce the age range of children at interview and partly because some of the target population had not been born at the time of the first phase selection.

Families of 18,800 selected children received letters of invitation to take part in the study sent by Medicare Australia. Families could 'opt-out' of the study by phoning an 1800 number or returning a reply-paid slip. Medicare Australia 1800 staff were given training about the study and were able to answer queries and make notes of other information (e.g. telephone numbers).

After a 4-week opt-out period, Medicare Australia gave the contact names and addresses of remaining families to I-view, the Wave 1 data collection agency. I-view then sent another letter to families saying when an interviewer would be in their area.

I-view maintained a 1800 number for families selected in the study, which was transferred to the ABS who took responsibility for the data collection from Wave 2 onwards.

11.2 Development and testing of survey instruments

11.2.1 Pre-testing

Pre-testing of new material and processes is undertaken at each wave of the study, comprising small-scale pre-tests and cognitive interviews. In Waves 1 and 2, more formal piloting was also undertaken. Small-scale testing is also undertaken for the between-wave surveys.

Wave 1
  • Development began in March 2002.
  • Small-scale pre-testing occurred in September-October 2002.
  • A pilot test with about 50 families from each cohort was conducted in March-April 2003.
Wave 2
  • Development began in July 2004.
  • Small-scale pre-testing occurred in September-October 2004.
  • A pilot test with 86 families was conducted in April 2005.
Wave 3
  • Development began in March 2006.
  • Pre-testing occurred in a number of stages from mid 2006 to March 2007.
  • No pilot test was required.
Wave 4
  • Development began in February 2008.
  • Pre-testing occurred in a number of stages from mid-August 2008 to June 2009.
  • No pilot test was required.
Wave 5
  • Development began in February 2010.
  • Pre-testing occurred in a number of stages from mid-June 2009 to March 2010.
  • No pilot test was required.
Wave 6
  • Development began in May 2012.
  • Pre-testing occurred in a number of stages from August 2012 to September 2013.
  • No pilot test was required.
Wave 7
  • Development began in May 2014.
  • Pre-testing occurred in a number of stages from August 2014 to September 2014.
  • No pilot test was required.

11.2.2 Dress rehearsal

In Wave 1, a dress rehearsal (DR) sample of 526 families was recruited to test the content and processes intended for the main waves of the study. Over 1,000 children were initially selected from 25 postcodes in Victoria, Sydney and rural/remote New South Wales and Queensland. Postcodes in Victoria were selected at random but the other postcodes were selected as areas that may provide challenges to the data collection process. Other dress rehearsals have also been completed.

  • Wave 1 DR - August-November 2003 (526 families interviewed)
  • Wave 2 DR - September-November 2005 (423 families interviewed)
  • Wave 3 DR - July-October 2007 (420 families interviewed)
  • Wave 4 DR - July-October 2009 (387 families interviewed)
  • Wave 5 DR - July-August 2011 (451 families interviewed)
  • Wave 6 DR - June-August 2013 (351 families interviewed)
  • Wave 7 DR - June-September 2015 (309 families interviewed)

After each dress rehearsal, both processes and content have been refined to increase efficiency and reduce the time in the home.

11.3 Data collection

11.3.1 Interview length

In Wave 1, an average of 126 minutes was allowed for time in the home by the interviewer. In-home data collection with the B cohort averaged about 1.5 hours, while interviews for the K cohort averaged about 2.5 hours.

In Wave 2, although an average of 90 minutes had been allowed for the time in the home, the actual time was shorter, averaging 66 minutes for the B cohort and 85 minutes for the K cohort.

In Wave 3, an average of 100 minutes was allowed for time in the home; the actual time was 91 minutes for the B cohort and 98 minutes for the K cohort.

In Wave 4, an average of 110 minutes was allowed for time in the home; the actual time was 102 minutes for the B cohort and 108 minutes for the K cohort.

In Wave 5, an average of 110 minutes was allowed for time in the home; the actual time was 98 minutes for both cohorts.

In Wave 6, an average of 110 minutes was allowed for time in the home; the actual time was 108 minutes for the B cohort and 116 minutes for the K cohort.

In Wave 7, an average of 110 minutes was allowed for time in the home; the actual time was 114 minutes for the B cohort and 115 minutes for the K cohort.

11.3.2 Interviewers

As part of a standard ABS interviewer induction, ABS interviewers receive two weeks of intensive training across a range of standard procedures and practices. All interviewers received eight hours of home learning (this included a computer-based learning module, home study exercises and the reading of interviewer instructions).

In Wave 1, 150 interviewers and field supervisors from I-view were trained during a series of four-day sequential training courses conducted in Melbourne, Brisbane, Perth and Sydney during February and early March 2004. The principal trainers were the same for all courses, ensuring consistency in training.

Psychologists conducted the training for 'Who am I?', the PPVT and the interviewer observations. A large part of the training involved practice interviews, with one day devoted to interviews with parents and children.

For Wave 2, 147 interviewers from ABS were trained in a series of three-day training courses in Sydney, Melbourne, Brisbane and Perth during March and April 2006. Two training teams were used, comprising staff from both AIFS and ABS. This time, AIFS staff undertook the direct assessment training, after receiving training from a child psychologist (the use of computer-assisted interviewing for the direct assessments helped ensure the consistent administration of these assessments).

For Wave 3, 176 interviewers from ABS were trained in a series of two-day training courses in Brisbane, Melbourne, Sydney and Perth during March and April 2008. Interviewers who had not worked on LSAC previously were given background training in LSAC before the two-day course commenced. Two training teams were used, comprising staff from ABS, AIFS and DSS. Again, AIFS staff undertook the direct assessment training.

For Wave 4, 181 interviewers from ABS were trained in a series of three-day training courses in Brisbane, Melbourne, Sydney and Perth. Two training teams were used, comprising staff from the ABS, AIFS and DSS. As in previous waves, AIFS staff undertook the direct assessment training.

For Wave 5, 198 interviewers from ABS were trained in a series of three-day training courses in Brisbane, Melbourne, Sydney, Adelaide and Perth. New-to-LSAC interviewers (defined as anyone who did not participate in Main Wave 4) attended the first day of classroom training where topics such as 'Background to the study', 'Physical measurements', 'Direct assessments' and 'Notebook security' were covered. All interviewers attended Days 2 and 3 when the P1 interviews and the K and B child interviews were covered in detail (apart from what was done on Day 1). New interviewers were teamed with an experienced interviewer, allowing for mentoring throughout the training course and for the new interviewers to be the interviewer during practice sessions.

For Wave 6, 200 interviewers from ABS were trained in a series of four-day training courses in Brisbane, Melbourne, Sydney, Adelaide and Perth. All interviewers attended the full four-day training program due to the large amount of new content and procedures. During the practice sessions, interviewers were split into groups of three (rather than pairs as in previous waves). This allowed for a more realistic practice with each interviewer taking the role of the parent, child and interviewer. Where possible in the training sessions and in the practice sessions, new LSAC interviewers were paired with experienced LSAC interviewers. ABS staff conducted all of the training.

For Wave 7, 200 interviewers were in the initial training sessions (March-April), and then another 20 in a top-up training held in July 2016. All interviewers attended the full four-day training program due to the large amount of new content and procedures. During the practice sessions, interviewers were split into groups of three (rather than pairs as in Waves 1-5). This allowed for a more realistic practice with each interviewer taking the role of the parent, child and interviewer. Where possible in the training sessions and in the practice sessions, new LSAC interviewers were paired with experienced LSAC interviewers. ABS staff conducted all the training.

11.3.3 Fieldwork periods

Wave 1

Selected postcodes were divided into two groups for maximum field efficiency. The target population was also divided into two groups: children born March-August (older) in one group and children born September-February (younger) in the other.

The fieldwork was divided into four phases:

  • Phase 1 started in mid-March 2004 for the older children in the first group of postcodes.
  • Phase 2 started at the end of April for the older children in the second group of postcodes.
  • Phase 3 started in June for the younger children in the first group of postcodes.
  • Phase 4 started in late July for the younger children in the second group of postcodes.

Follow-up continued throughout 2004. The blue line in Figure 6 shows the distribution of interviews over time for Wave 1 fieldwork.

Wave 2

Again, there were broadly four fieldwork periods, although the dates for these varied from state to state. Regional offices of the ABS were able to organise the work to suit the availability of interviewers and other work. As far as possible, ABS tried to interview the children born in March-August in the first two periods, and children born in September-February in the later fieldwork periods. Eighty-four per cent of the interviews were conducted prior to September 2006.

Figure 6 shows the distribution of interviews over time for the Wave 2 fieldwork. Fieldwork started later than in Wave 1 due to the additional work required to prepare the CAI instrument.

Wave 3

Fieldwork was organised as per Wave 2. The green line in Figure 6 shows the distribution of interviews over time for the Wave 3 fieldwork.

Wave 4

As the children get older, the age differences within a cohort are less significant. To assist the efficiency of work allocations to interviewers, the focus in Wave 4 was more on the location of the sample and interviewers with less emphasis given to following interviews within the set phases. The dark blue line in Figure 6 shows the distribution of interviews over time for the Wave 4 fieldwork.

Wave 5

Fieldwork was organised based on the location of the sample and interviewers. Figure 6 shows that the distribution of interviews for the Wave 5 fieldwork was more spread out across the months than for previous waves.

Wave 6

Fieldwork was organised based on the location of the sample and interviewers. Figure 6 shows that the distribution of interviews for the Wave 6 fieldwork was distributed across the months, similar to Wave 5.

Wave 7

Fieldwork was organised based on the location of the sample and interviewers. Figure 6 shows that the distribution of interviews for Wave 7 decreased greatly in September, which can be mostly attributed to the ABS Census Post Enumeration Survey priorities during this time. Enumeration was extended from the originally planned end in December 2016 to May 2017.

Figure 6: Month of interview for study families in Waves 1 to 7

Figure 6: Month of interview for study families in waves 1 to 7

11.3.4 Contact process

Wave 1

For most families, the interviewer only had the name and address of the Medicare cardholder and which cohort the child was in. In a small number of cases, families who were keen to participate had contacted the 1800 numbers and supplied phone numbers and/or best times to call.

Interviewers were required to make up to six visits to the address, at different times of the day and on different days of the week. A major challenge was that 7% of addresses were post office box addresses, and although families with these addresses were specifically requested to make contact with the 1800 number to supply a residential address, only a small proportion did so. In addition, many of the residential addresses held by Medicare were found to be out of date by the time the interviewers visited. Interviewers made significant attempts to locate families for whom they did not have a current residential address, by referencing the White Pages and electoral rolls and speaking with neighbours and other local contacts.

Between waves

Contact is maintained with study families between waves by sending birthday cards, annual calendars and newsletters and via the between-wave mailout and online questionnaires. These processes have resulted in some families contacting the ABS to update their contact information, which helps when trying to arrange appointments for the main waves of interviewing.

Subsequent waves

Pre-interview letters plus a brochure outlining the processes for that wave were sent to all families who had not opted out of the study since the previous wave, unless it was confirmed that the address was out-of-date. Interviewers then followed up with a telephone call to make an appointment for an interview. If the contact information was out-of-date, the interviewers tried to contact secondary contacts of P1 (these details were given by P1 in Wave 1 and are updated each wave) to locate the family. One visit to the address was also made. If the family could not be located, the interviewer referred this back to the office for tracking.

After an appointment for interview was made, the interviewer confirmed the appointment the day before the appointment.

11.3.5 Foreign language interviews

Wave 1

As part of the Medicare Australia mailout, a brochure was included with information about the study in nine languages. Medicare Australia staff made use of the Telephone Interpreter Service (TIS) to assist with calls where required.

Apart from this brochure, no other study material was (or has been) translated into other languages, and instead interpreters were used. An interpreter was required in 3% of interviews, with over 50 languages involved. In most cases (138), a member of the family or friend was preferred as the interpreter. In 76 cases, an I-view employee was able to act as interpreter and, in 96 cases, an interpreter was employed.

Wave 2

A total of 110 interviews (1%) were conducted in a language other than English, in 23 different languages. Family or friends assisted in 58 cases, ABS interpreters helped in 37 cases, and a TIS interviewer was used for 15 families. An interpreter was arranged whenever requested or judged necessary by the interviewer. The reduction in use of interpreters between waves is presumably due to the increased confidence in English that had been gained by respondents in this time.

Wave 3

A total of 97 interviews needed an interpreter, in 24 languages. Family or friends assisted in 58 cases, ABS interpreters helped in 31 cases, and a TIS interviewer was used for eight families.

Wave 4

A total of 93 interviews needed an interpreter, in 26 languages. Family or friends assisted in 50 cases, ABS interpreters helped in 29 cases, and a TIS interviewer was used for 14 families.

Wave 5

A total of 81 interviews needed an interpreter, in 18 languages. Family or friends assisted in 47 cases, ABS interpreters helped in 24 cases, and a TIS interviewer was used for 10 families.

Wave 6

A total of 64 interviews needed an interpreter, in 17 languages. Family or friends assisted in 42 cases, ABS interpreters helped in 18 cases, and a TIS interviewer was used for four families.

Wave 7

A total of 55 interviews needed an interpreter, in 19 languages. Family or friends assisted in 31 cases, ABS interpreters helped in 21 cases, and a TIS interviewer was used for three families.

11.3.6 Indigenous communities

Although the sample selection process excluded 40% of areas classified as remote by the ABS (areas that typically have a high Indigenous population) there were still a number of postcodes selected that contained some remote Indigenous communities, hence strategies have been put in place to enumerate these communities.

Where feasible, communities were visited or telephoned, and personal contact made with a number of community organisations from whom assistance was gained to identify whether families were in residence and willing to be interviewed. Travel to remote communities was only undertaken if there was an appointment for an interview.

Aboriginal and Torres Strait Islander families are included in representative numbers in non-remote centres. However, there has been a higher rate of attrition from the study among these families. See the weighting and non-response technical papers for more details.

11.3.7 Remote areas

In the initial sample, there were 12 postcodes selected in areas classified as 'remote' by the ABS Australian Standard Geographic Classification (ASGC) Remoteness Classification. Interviewers were either recruited from these areas or travelled to these areas when the field agency did not have a suitable interviewer in the locality.

Where visits were not possible, telephone interviews were conducted: 12 (0.12%) in Wave 1, 42 (0.46%) in Wave 2, 87 (0.10%) in Wave 3, 83 (0.99%) in Wave 4, 73 (0.91%) in Wave 5, 59 (0.81%) in Wave 6 and, in Wave 7, 49 (0.76%) of call interviews were conducted when visits were not possible.

11.4 Fieldwork response

11.4.1 Wave 1 recruitment

The final response to the recruitment of children was 54% of those families who were sent the initial letter by Medicare Australia. The response rate was higher for the B cohort, with 57% of families (5,107) agreeing to take part, compared with 50% of K cohort families (4,983).

About 35% of families who were sent the initial letter refused to take part in the study. The main reasons given to interviewers for not participating in the study were: not interested/too busy (57%), not capable/moving/overseas (9%), husband refused (9%), and illness/death (8%). The remaining 13% of families could not be contacted, despite intensive efforts from interviewers.

Non-response analysis was undertaken to determine how representative the sample is of all Australian children in the scope of this study, and adjustments have been made to the survey weights to allow for this. For further information on the weighting and non-response, see LSAC Technical Paper No. 3, Wave 1 weighting and non-response analysis [PDF 1.4 MB].

11.4.2 Response in later waves

Table 13 summarises the response from families in later waves, using the Wave 1 sample and 'available' sample as the bases for comparisons.

Table 13: Sample size and response rate for each wave and cohort of LSAC
  B cohort K cohort Total
  n Resp. rate of
Wave 1 (%)
Resp. rate of
available sample (%)
n Resp. rate of
Wave 1 (%)
Resp. rate of
available sample (%)
n Resp. rate of Wave 1 (%) Resp. rate of
available sample (%)
Main waves
Wave 1 original 5,107 100   4,983 100   10,090 100  
Wave 2 availablea 5,047 98.8   4,913 98.6   9,960 98.7  
Wave 2 respondingb 4,606 90.2 91.2 4,464 89.6 90.9 9,070 89.9 91.1
Wave 3 available 4,971 97.3   4,829 96.9   9,800 97.1  
Wave 3 responding 4,386 85.9 88.2 4,331 86.9 89.7 8,717 86.4 89.0
Wave 4 available 4,929 96.5   4,774 95.8   9,703 96.2  
Wave 4 responding 4,242 83.0 86.0 4,169 83.7 87.3 8,411 83.4 86.7
Wave 5 available 4,884 96.6   4,735 95.0   9,619 95.3  
Wave 5 responding 4,085 80.0 91.1 3,956 79.4 83.5 8,041 79.7 83.6
Wave 6 available 4,483 87.8   4,395 88.2   8,878 88.0  
Wave 6 responding 3,764 73.7 84.0 3,537 71.0 80.5 7,301 72.4 82.2
Wave 7 available 4,318 84.6   4,176 83.8   8,494 84.2  
Wave 7 3,381 66.2 78.3 3,089 62.0 74.0 6,470 64.1 76.2
Between waves
Wave 1.5 sent 5,061 99.1   4,935 99.0   9,996 99.1  
Wave 1.5 returned 3,573 70.0 70.6 3,584 71.9 72.6 7,157 71.0 71.6
Wave 2.5 sent 4,859 95.1   4,712 94.6   9,571 94.9  
Wave 2.5 returned 3,268 63.5 64.0 3,287 65.5 66.0 6,555 63.4 65.0
Wave 3.5 sent 4,772 93.4   4,641 93.1   9,413 93.3  
Wave 3.5 returned 3,012 59.0 63.1 2,972 59.6 64.0 5,984 59.3 63.6

Notes: Excludes in-between waves 4.5 and 5.5 where the data is not relevant for users of the LSAC datasets. They were used only to update contact details. a Available sample excludes those who opted out of the study between waves. Some additional families also opted out permanently during the fieldwork process. b Those who had a home visit.

Table 14 details the reasons why interviews were not obtained in Waves 2-7.

Table 14: Response status and reasons for non-response by wave
Response status Wave 2 Wave 3 Wave 4 Wave 5 Wave 6 Wave 7
n % n % n % n % n % n %
Responding 9,070 91.1 8,717 89.0 8,411 86.6 8,041 83.6 7,301 82.2 6,470 76.2
Refusal 284 2.8 436 4.4 637 6.6 774 8.0 938 10.6 1,118 13.2
Non-contact 540 5.4 552 5.6 526 5.4 715 7.4 555 6.3 803 9.5
Away entire enumeration period 61 0.6 93 1.0 135 1.4 88 0.9 39 .4 34 0.4
Death of study child 5 0.1 1 0.01 0 0 1 0.01 3 0.0 2 0.0
Other N/A N/A N/A N/A N/A N/A N/A N/A 43 0.5 67 0.08
Total starting sample 9,960 100.0 9,799 100.0 9,709 100.0 9,619 100.0 8,879 100 8,494 100.0