3. Instruments
The Longitudinal Study of Australian Children Data user guide

Table 1 summarises the data collection instruments used in each wave.

Table 1. Data collection modes by wave
Questionnaire Mode Completed by Indicator Variable W1 W2 W3 W4 W5 W6

Notes: The indicator variable can be used to see if data is present or not for a particular instrument (for more information see sections 8.6 & 8.7). The [*] in the indicator variable should be replaced by the age indicator (a, c, d, e, f, g or h) as discussed below. In-between waves were administered using mail out surveys for Waves 1.5, 2.5 and 3.5. Waves 4.5 and 5.5 used online web forms to update contact details.

Face-to-Face Interview (F2F)

Paper Parent 1 N/A BK - - - - -
Face-to-Face Interview (F2F) Computer Parent 1 N/A - BK BK BK BK BK
Parent 1 during interview (P1D) Paper Parent 1 [*]p1dd BK BK BK - - -
Parent 1 during interview (CASI) Computer Parent 1 [*]p1dd - - - BK BK BK
Parent 1 Leave behind (P1L) Paper Parent 1 [*]p1scd BK BK BK - - -
Parent 2 Leave behind (P2L) Paper Parent 2 *]p2scd BK BK BK BK BK BK
Child Self Report (CSR) Computer Study Child [*]csrd - K K B BK BK
Audio Computer Assisted Interview (ACASI) Computer Study Child Need consent from: P1 [*]id40e & SC [*]id40f - - - K K K
Time Use Diary (TUD) Paper Parent 1 N/A BK BK BK - - -
Time Use Diary (TUD) Computer Study Child Need consent from: P1 [*]id40i & SC [*]id40j - - - K K K
Parent Living Elsewhere (PLE) Paper - mailed out PLE [*]plescd - BK - - - -
Parent Living Elsewhere (PLE CATI) Computer/ Telephone PLE [*]plescd - - BK BK BK BK
Home-Based Carer (HBC) Paper Carer [*]hbccbc B B - - - -
Centre-Based Carer (CBC) Paper Carer [*]hbccbc B B - - - -
Teacher Questionnaire (TQ) Paper Teacher [*]tcd K K BK BK BK BK
Physical Measurements (PM) Computer Study Child Need consent from: P1 [*]id30d & SC [*]id30e BK BK BK BK BK BK
Who Am I (WAI) Computer Study Child cid44a1 K - B - - -
PPVT Assessment (PPVT) Computer Study Child [*]ppvtd K K BK B B -
Matrix Reasoning (MR) Computer Study Child [*]id44a1 - K K BK B B
Study Child Blood Pressure (BP) Computer Study Child Need consent from: P1 [*]id47a & SC [*]id47b - - - K K B
Interviewer Observations (IOBS) Computer Interviewer BK BK BK BK BK BK
Executive functioning (EXEC - CogSTATE) Computer Study Child [*]id40m [*]id40n - - - - - K

The following methods are used to collect study data.

3.1 Child assessments

3.1.1 Physical measurements

Weight

For the B cohort in Wave 1, the child's weight was obtained by calculating the difference between the weight of Parent 1 (or another adult) with the child and the weight of the parent/other adult on their own. For the B cohort at all subsequent waves, and the K cohort at all waves, the child's weight was measured directly.

In Wave 1 the scales used were Salter Australia glass bathroom scales (150 kg x 50 g). In Waves 2 and 3, these scales were used along with HoMedics digital BMI bathroom scales (180 kg x 100 g). In Waves 4, 5 and 6, Tanita body fat scales were used.

Height

Height is measured for children aged 2 years and older. In Waves 1, 2 and 3, height was measured using an Invicta stadiometer, from Modern Teaching Aids. In Waves 4, 5 and 6, a laser stadiometer was used. Two measurements were taken, and if the two measurements differed by 0.5 cm or more, a third measurement was taken. The average of the two closest measures was included on the data file.

Girth

This measurement is taken for children aged 2 years and older using a non-stretch dressmaker's tape, positioning the tape horizontally over the navel. In all waves, two measurements were taken, and if these differed by 0.5 cm or more, a third measurement was taken. The average of the two closest measures was recorded on the data file.

Body Fat

A body fat measurement was included in Waves 4, 5 and 6, with the reading provided by the same scales used for weight (Tanita body fat scales). Issues with the body-fat measurement are outlined in the Data Issues Paper.

Head circumference

This measurement was only taken for the B cohort in Wave 1, using an Abbott head circumference tape. Two measurements were taken, and if these differed by 0.5 cm or more, a third measurement was taken. The average of the two closest measures was included on the data file. 

Blood pressure

This measurement was taken for the K cohort in Waves 4 and 5 and for the B cohort in Wave 6 using the A&D Digital Blood Pressure Monitor - Model UA-767. The interviewer took two measurements, with a one-minute interval between the measurements. Both of the readings were included in the data file.

3.1.2 Who am I? (WAI)2

The "Who am I?" assessment is a direct child assessment measure that requires children to copy shapes (a circle, triangle, cross, square and diamond) and write numbers, letters, words and sentences. For the LSAC testing, there was a change to "Who Am I?", Item 11: "This is a picture of me" was replaced with a sentence to be copied, "John is big". The  "Who am I?" assessment was used for children aged 4-5 years (Wave 1 K cohorts and Wave 3 B cohorts) to assess the general cognitive abilities needed for beginning school.

The study child was given his/her own answer booklet to draw and write in. What they wrote/drew was assessed by experienced researchers at the Australian Council for Educational Research (ACER). See Data Issues Waves 1 to 6 for details of the Rasch Modelling used to score the WAI.

3.1.3 Peabody Picture Vocabulary Test (PPVT)3

A short form of the Peabody Picture Vocabulary Test (PPVT-III), a test designed to measure a child's knowledge of the meaning of spoken words and his or her receptive vocabulary for Standard American English, was developed for use in the study. This adaptation is based on work done in the USA for the Head Start Impact Study, with a number of changes made for use in Australia.

Different versions of the PPVT containing different, although overlapping, sets of items of appropriate difficulty were used for the children at ages 4-5, 6-7 and 8-9 years. A book with 40 plates of display pictures was used. The child points to (or says the number of) a picture that best represents the meaning of the word read out by the interviewer.

Scores are created via Rasch Modelling so that changes in scores represent real changes in functioning, rather than just changes in position relative to peers. See Data Issues Waves 1 to 6 for more details.

3.1.4 Matrix Reasoning4

Children completed the Matrix Reasoning (MR) test from the Wechsler Intelligence Scale for Children, 4th edition (WISC-IV) at ages 6-7, 8-9 and 10-11 years. This test of non-verbal intelligence presents the child with an incomplete set of diagrams (an item) and requires them to select the picture that completes the set from five different options. The data file includes raw scores (number of correct responses) and scaled scores based on age norms given in the WISC-IV manual. The instrument comprises 35 items of increasing complexity. Children start on the item corresponding to their age-appropriate start point. If a child does not answer correctly on the first or second start-point items, the examiner should ask two items prior to the age-appropriate start point (called "reverse administration"). Reverse administration was not implemented in the LSAC instrument. See the discussion of this issue in See Data Issues Waves 1 to 6.

3.1.5 Executive functioning (EXEC/CogState)

The executive functioning of children in the K cohort was tested from Wave 6 using the Groton Maze Learning Test (GML). The outcome variables are contained in the CogState dataset, where a series of cognitive testing batteries have been customised for use in LSAC. Each row of a CogState dataset represents one task in the CogState test battery for one study subject in one test session. Each column represents demographic information or an outcome variable.

The GML test contains five learning trials (i.e. the subject repeats the same task five times), where the child is shown a 10 x 10 grid of tiles on a computer touch-screen. A 28-step pathway is hidden among these 100 possible locations. The child is instructed to move one step from the start location and then to continue, one tile at a time, toward the end. The subject repeats the task while trying to remember the pathway they have just completed and learns the 28-step pathway though the maze on the basis of trial and error feedback. The scores are interpreted by calculating the total number of errors made in attempting to learn the same hidden pathway. A lower score indicates better performance.

3.1.6 Rice Test of Grammaticality Judgement (GJT/SLI)

As children grow older different methods are needed to assess the presence or absence of specific language impairment (SLI). That is, to identify whether children are meeting expected performance levels in achieving the adult standard of English grammar. Where LSAC children were identified in early waves to have poor language performance, it was not possible to distinguish the children with and without SLI. The Rice Grammaticality Judgement Task (GJ Task) was therefore introduced in Wave 6 for children of the K cohort.

The GJ Task is a short, automated (administered by ACASI) task that requires the study child to distinguish between grammatical and non-grammatical utterances known to be vulnerable to SLI in English-speaking children (Rice, Hoffman and Wexler, 2009). The study child listens through earphones as 20 pre-recorded items are spoken and enters their response by clicking the appropriate radio buttons (1 for "Right", 5 for "Not so good", and 9 for "Hear again"). Its sensitivity and specificity for SLI are .70 with a ROC of approximately 0.85.

3.2 Response rates

The number and percentages of survey instruments of each type that were completed at each wave are shown in Table 2. More detailed information on non-response can be found in the technical papers on weighting and non-response.

Table 2. Waves 1-5 instrument response
  B cohort K cohort
  Eligible (b) Actual (c) % Eligible (b) Actual (c) %
Wave 1 Instrument (a)
F2F 5,107 5,107 100 4,983 4,983 100
P1L 5,107 4,341 85 4,983 4,229 85
P2L 4,630 3,696 80 4,286 3,388 79
TUD 1 5,107 4,031 79 4,983 3,867 78
TUD 2 5,107 3,751 73 4,983 3,582 72
AI N/A N/A N/A 4,983 4,880 98
PPVT N/A N/A N/A 4,983 4,382 88
HBC 788 342 43 N/A N/A N/A
CBC 436 233 53 N/A N/A N/A
TQ N/A N/A N/A 4,761 3,276 69
AEDC N/A N/A N/A 1,366 720 53
W1.5 5,061 3,573 71 4,935 3,594 73
Wave 2 Instrument (a)
F2F (d) 5,107 4,606 90 4,983 4,464 90
P1D 4,606 4,504 98 4,464 4,358 98
P1L 4,606 3,536 77 4,464 3,495 78
P2L 4,099 3,128 76 3,804 2,949 78
TUD 1 4,606 3,477 75 4,464 3,446 77
TUD 2 4,606 3,459 75 4,464 3,460 78
PPVT N/A N/A N/A 4,464 4,409 99
MR N/A N/A N/A 4,464 4,402 99
PLE Mail-out 400 96 24 612 199 33
HBC 791 533 67 N/A N/A N/A
CBC 1,672 1,144 68 N/A N/A N/A
TQ N/A N/A N/A 4,447 3,632 82
W2.5 5,107 3,246 64 4,983 3,252 65
Wave 3 Instrument (a)
F2F (d) 5,107 4,386 86 4,983 4,331 87
P1D 4,386 3,831 87 4,331 3,807 88
P2L 3,900 2,753 71 3,707 2,680 72
TUD1 4,386 2,959 67 4,331 2,961 68
TUD2 4,386 2,950 67 4,331 2,963 68
PPVT 4,386 4,266 97 4,331 4,273 99
WAI 4,386 4,197 96 N/A N/A N/A
MR N/A N/A N/A 4,331 4,270 99
PLE CATI 346 272 77 510 403 79
TQ 4,114 3,395 83 4,275 3,643 85
Wave 4 Instrument (a)
F2F (d) 5,107 4,242 82 4,983 4,164 84
CASI 4,242 4,210 99 4,164 4,116 99
P2L 3,706 2,677 72 3,512 2,645 75
CSR 4,242 4,181 99 N/A N/A N/A
ACASI N/A N/A N/A 4,169* 4,094 99
TUD N/A N/A N/A 4,169* 3,994 96
PPVT 4,242 4,185 99 N/A N/A N/A
MR 4,242 4,180 99 4,169* 4,103 99
PLE CATI 439 377 86 572 493 86
TQ 4,143 3,427 83 4,025 3,352 83
Wave 5 Instrument (a)
F2F (d) 5,107 4,085 80 4,983 3,956 79
CASI 4,077 4,010 98 3,952 3,857 98
P2L 3,512 2,444 70 3,277 2,333 71
CSR 4,026* 4,014 100 3,872 3,850 99
ACASI N/A N/A N/A 3,873* 3,844 99
TUD N/A N/A N/A 3,871* 3,649 94
PPVT 4,026 3,977 99 N/A N/A N/A
MR 4,027 3,985 99 N/A N/A N/A
PLE CATI 537 404 75 614 464 76
TQ 4,021 3,490 87 3,857 3,225 84
Wave 6 Instrument (a)
F2F (d) 5,107 3,764 74 4,983 3,537 71
CASI 3,759 3,668 98 3,526 3,376 96
P2L 3,197 2,311 72 2,904 2,212 76
CSR N/A N/A N/A 3388 3,317 98
ACASI 3,648* 3,597 99 3,386* 3,313 98
TUD 3,649* 3,460 95 3,387* 3,071 91
EXEC N/A N/A N/A 3,386* 3,333 98
PPVT N/A N/A N/A 3,386* 3,281 97
MR 3,648* 3,585 98 N/A N/A N/A
PLE CATI 559 398 71 554 420 76
TQ 3,678 3,102 84 3,422 2,698 79

Notes: * Represents instances where a child interview was completed and the main interview with the parents was not. Specifically, in Wave 4 there were five cases (K cohort). In Wave 5 there were eight cases for the K cohort and four cases for the B cohort. In Wave 6 there were eleven cases for the K cohort and four cases for the B cohort. N/A = Not administered
a Questionnaire acronyms are detailed above in section 3, Table 1: Data collection modes by wave.
b "Eligible" means the number of LSAC children for whom a questionnaire was applicable (e.g. children are eligible for a HBC questionnaire if the child’s main care is attended for 8 hours or more per week and this is home-based care).
c "Actual" means the number of respondents for whom a form was returned. d Response rates for Waves 2 to 6 as a proportion of Wave 1 families.

3.2.1 Parent 1 questionnaires

In Wave 1, interviewers encouraged the parents to complete the P1L and P2L forms while the interviewer was in the home. Interviewers were also able to pick up forms in some cases, when forms were left behind. Forms not given to interviewers were mailed back. Two reminders were made for forms that were not returned.

In Wave 2, Parent 1 had two forms to complete. Interviewers were instructed that the P1D form must be completed when they were in the home (resulting in a high response rate). The P1L was generally left behind to be mailed back, as there was not enough time for these to be completed. Interviewers were generally not required to pick up the forms. Up to four reminders were made for forms that were not returned; however, the P1L forms showed lower response rates in Wave 2 compared with Wave 1. This may have been because P1 had already completed one form or because interviewers did not generally pick up forms.

For Wave 3, there was only one Parent 1 self-complete form. Interviewers were instructed that this form must be completed while the interviewer was in the home. However, only two thirds of parents were able to do so. Three reminders were given for forms not returned.

In Wave 4, Parent 1 was asked to complete a CASI, which resulted in a response rate of 99% of eligible respondents. This was higher than the response rate of 88% of eligible respondents achieved in Wave 3 using the self-complete form.

In Wave 5, response rates were very similar to response rates obtained in Wave 4. This was due to no mode changes and attrition tapering off.

In Wave 6, response rate are similar to previous waves using the same mode. There is a slight decrease from the K cohort completion of the CASI from 98% in Wave 5 to 96% in Wave 6.

3.2.2 Parent 2, TUD and teacher forms

Response rates to the P2L and the TUD were broadly similar between waves (Waves 1, 2 and 3) at between 67 and 79%, while the carer and teacher questionnaire response rates were much improved in Wave 2, with similar response rates at Wave 3. In Wave 4 the TUD response rate was 96%. The higher response rate could be contributed to changes in the procedure and in the informant. In Waves 4, 5 and 6, the interviewer collected the TUD information from the child instead of the parent. The data were collected as part of the interview rather than leaving a diary that previously required completion and return via mail by respondent families after the visit.    

3.2.3 PLE response

The PLE questionnaire was introduced in Wave 2 and applies to children who see their "parent living elsewhere" (PLE) at least once a year. There are three stages at which non-response can occur: (1) obtaining contact details from Parent 1; (2) obtaining permission from Parent 1; and (3) receiving a response from the PLE.

In Wave 2, contact details were given for 69% of cases for the B cohort and 70% of cases for the K cohort, and responses were received from 35% of PLEs sent a questionnaire for the B cohort and 47% for the K cohort.

Due to the relatively low response in Wave 2 to the mail-out questionnaire, a change in methodology was introduced in Wave 3. Where Parent 1 had provided contact details, PLEs were telephoned and asked to respond to a computer-assisted telephone interview (CATI). The response from PLEs who were approached was very positive. Of the 856 PLEs that interviewers attempted to contact, interviews were achieved with 675 (79%) and only 53(6%) refused an interview. Most of the remaining non-responses were due to not being able to contact the PLE.

In Wave 3, Parent 1 was explicitly asked for their permission to contact the PLE. Therefore, it was easy for Parent 1 to refuse to provide any information about the PLE or refuse the PLE's participation. This meant that no information was obtained for 260 (18%) PLEs.

It is worth noting that from Wave 2 onwards, there was no direct question asking the Parent 1 permission to contact the PLE: some Parent 1 respondents refused the PLE's participation.

Table 3 summarises the situation with regard to PLEs for Waves 3 to 6.

Table 3. Waves 3 and 4: Information obtained with regard to PLE.
  Wave 3 Wave 4 Wave 5 Wave 6
  B K Total B K Total B K Total B K Total
PLE identified during P1 interview 578 837 1,415 674 878 1,552 773 911 1,684 778 817 1,595
Eligible PLE* 346 510 856 439 572 1,011 537 614 1,151 559 554 1,113

Note: *The PLE is considered eligible when: (1) the PLE satisfies the parental requirements; i.e. PLEs who see the study child at least once a year; (2) the PLE¬Ďs contact details are available; (3) Parent 1 did not explicitly refuse permission to contact the PLE.

Footnotes

2 The "Who Am I?" is copyrighted by the Australian Council for Educational Research, Melbourne, 1999.

3 The Peabody Picture Vocabulary Test, Third Edition (PPVT-III) Form IIA is copyrighted by Lloyd Dunn, Leota Dunn, Douglas Dunn, American Guidance Service, Inc., 1997, and published exclusively by AGS Publishing. Permission to adapt and create a short form for LSAC was granted by the publisher. The PPVT - III - LSAC Australian Short-form was developed by S. Rothman, Australian Council for Educational Research (ACER), Melbourne, from the Peabody Picture Vocabulary Test, Third Edition (PPVT-III), Form IIA, English edition.

4 The Wechsler Intelligence Scale for Children, Fourth Edition is copyrighted by Harcourt Assessment, Inc., 2004.

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