CONCLUSIONES 353 5 SUMMARY

Children’s cognitive abilities in early life have been shown to be a good indicator of their later educational development (Feinstein, 2003). Although research suggests that cognitive ability is one of the most heritable of traits (Plomin, DeFries, McClearn & Rutter, 1997), longitudinal studies like Growing Up in Ireland facilitate an exploration of how cognitive abilities develop over time and how they affect, and are affected by, other factors that influence children’s opportunities and outcomes.

At 5 years old, children have not yet taken part in any national tests of cognitive ability in school or preschool. In the absence of such test results, a direct measure of cognitive ability administered during the course of the study was deemed to be the best way to obtain an objective and standardised measurement of this important area of children’s development. Although a number of instruments for measuring cognitive ability in children exist (see Lichtenberg, 2005 for a review), the challenge faced by the Study Team at Wave 2 (when the children were age 3) was to find an instrument which possessed strong measurement properties and could be adapted for use in a large social research survey such as Growing Up in Ireland. After consultation and piloting, it was decided to use the British Ability Scales with the Infant Cohort at 3 years of age. This was continued with the 5-year-olds for longitudinal consistency.

5.2 THE BRITISH ABILITY SCALES

5.2.1 THE NATURE OF THE TEST AND SUBSCALES USED

The BAS is organised into two batteries: an Early Years Battery which can be used with children aged 2 years and 6 months to 5 years and 11 months of age, and a School Aged Battery covering the ages 6 to 17 years and 11 months of age. The former was used in the current study.

Given the time constraints under which the study team was operating (90 minutes contact time in the home), it was not feasible to administer the full Early Years Battery. Instead, the study team chose two of the core scales (Naming Vocabulary and Picture Similarities) to derive a measure of children’s verbal and non-verbal ability – suitable for children at ages three and five years old.

The Naming Vocabulary test serves as a measure of children’s expressive English language vocabulary. It consists of 36 items ordered in terms of increasing difficulty and children are required to name the item displayed from a picture book. The Picture Similarities test comprises 33 items and measures children’s reasoning capacity and problem-solving skills. In

this test, children are given a picture card and are required to choose from four stimulus alternatives, the element or concept which they share (e.g. they are both cuddly toys, they both fly etc.).

The British Ability Scales (BAS) was ultimately selected for use with the 3-year-olds in the Infant Cohort for a number of reasons. It facilitates direct participation by the Study Child him/herself. It provides different subscales, thus allowing the researcher to choose which to administer, thus reducing respondent burden on the child. It is also used in studies such as Growing Up in Scotland and the Millennium Cohort Study, thus allowing an international comparison of how children in Ireland are faring and developing compared with their counterparts abroad. The scale can be used with children up to 17 years and 11 months. This is very important in a longitudinal study like Growing Up in Ireland.

The experience of fieldwork with the 3-year-olds (as well as the pilot work undertaken with the 5-year-olds)42 _{established the feasibility of the test being administered by general purpose} social science interviewers, largely with the assistance of a CAPI program which was developed to implement the complex decision rules determining which items should be presented to the child, based on their response patterns of prior questions in the test. The CAPI program also helped to standardise the administration of tests in terms of prompting the interviewer when teaching is required and when they should query an answer.

5.2.2 PSYCHOMETRIC INFORMATION

Reliability

Standardisation for children aged 5 was carried out on 124 children.43 _{Elliot et al (1997) report} co-efficient alphas of 0.65 for the Naming Vocabulary test for children aged 5:0 – 5:11. The corresponding alpha for the Picture Similarities test is 0.81. The test constructors do not report test-retest reliability estimates for the BAS Early Year scales. However, test-retest correlations for the American version of the BAS (the DAS) are estimated at 0.89 for the Naming Vocabulary and 0.63 for the Picture Similarities test for the age band 5:0 – 6:3 years of age.

Validity

Elliot et al (1997) report that the BAS composite verbal, non-verbal and GCA scores are substantially correlated with the verbal, performance and full-scale IQ scores on both the WPPSI-R and the WISC. The Naming Vocabulary and Picture Similarities subtests of the BAS

42 _{See Thornton and Williams, 2016.}

43 _{The reader should note that the analysis provided here from the pilot survey at 5 years is based on a}

correlated 0.68 and 0.47 with the verbal and performance IQ components of the WPPSI-R respectively.

5.3 ANTHROPOMETRIC MEASUREMENT

Height and weight have long served as leading indicators of children’s physical health and development, and it is becoming increasingly apparent that the period from infancy through early childhood is a critical one for growth and development (Cameron, 2007). An emerging body of research suggests that early growth patterns may have implications for health and development over the life-course (Singhal, Fewtrell, Cole et al, 2003).

Data captured at 5 years of age can be compared to data collected at Waves 1 and 2 and allow for modelling of growth trajectories and how these are affected by a range of other variables including breastfeeding, child health status, parental height and weight, diet and social characteristics.

Children’s height was measured by trained interviewers using a Leicester portable height stick and a SECA 761 flat mechanical weighing scales.

Chapter 6

PROCEDURES & QUESTIONNAIRES

USED IN THE SCHOOL

6. PROCEDURES & QUESTIONNAIRES USED IN THE SCHOOL