A key aspect of the NCDS, BCS and MCS is that they each provide a number of high quality child cognitive assessments. The full battery of cognitive tests available for use in the NCDS, BCS and MCS are shown in Table 4.1. All cognitive tests were standardised to have a mean of 0 and a SD of 1 for analysis. For a full description of each of the cognitive tests, please see Appendix 4B.
In this chapter I was concerned not only by the level of socioeconomic inequality in child cognitive ability, but also whether the strength of relationship has changed significantly over time. Analysing the strength of the relationship over time requires generally comparable cognitive tests across the separate cohort studies. The test scores concerning the same measure of cognitive ability at the same age are described in Table 4.2.
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Table 4.1- Child cognitive tests in the NCDS, BCS and MCS
Study Cognitive Test Authors Variable(s) Used
NCDS Southgate Reading Test (Age 7) Southgate (1962) n92
Copying Designs Test (7) NCDS n457
Drawing-A-Man Test (7) Goodenough (1926) n1840
Problem Arithmetic Test (7) Pringle et al., (1966) n90
General Ability Test (Age 11) Douglas (1964) n914, n917
Reading Comprehensive Test (11) NFER (1969) n923
NFER Arithmetic Test (11) NFER (1969) n926
NFER Copying Test (11) NFER (1969) n929
BCS Human Figure Drawing Test (Age
5)
Goodenough (1926) f121
Copying Designs Test (5) Rutter et al., (1970) f119
English Picture Vocabulary Test (5) Brimer and Dunn (1962)
BD2READ
Complete-A-Profile Test (5) Goodenough (1926) f118
Friendly Maths Test (Age 10) NCDS BD3MATHS
Shortened Edinburgh Reading Test (10)
Thompson Unit (1978)
BD3RREAD
BAS Word Definitions (10) Elliott et al., (1979) i3504- i3540
BAS Recall Digits (10) Elliott et al., (1979) i3541- i3574
BAS Similarities (10) Elliott et al., (1979) i4201- i4221
BAS Matrices (10) Elliott et al., (1979) i3617- i3644
MCS BAS Picture Similarities (Age 5) Elliott et al., (1979) ccpsco00
BAS Naming Vocabulary (5) Elliott et al., (1979) cdnvabil
BAS Pattern Construction (5) Elliott et al., (1979) cccsco00
BAS Word Reading (7) Elliott et al., (1979) DCWRSD00
BAS Pattern Construction (7) Elliott et al., (1979) DCWRSD00
NFER Progress in Maths (7) NFER (1969) MATHS7SA
BAS Verbal Similarities Age (11) Elliott et al., (1979) EVSTSCO
59 Table 4.2- Generally comparable cognitive tests
National Child Development Study Millennium Cohort Study Problem Arithmetic Test Age 7 (Pringle et al., 1966) 10 problems graded in level of difficulty, which could either be read by the children themselves or read to them by a teacher. One mark is awarded for each correct answer, and is therefore scored between 0 and 10. NFER Progress in Maths Test Age 7 (NFER 2007)
Covers topics such as numbers, shapes, measurement and data handling. Although there are 20 test items, the test is scored out of 12, 16 or 20 depending on the scores from the initial 7 test items. Verbal Subset
of the General Ability Test
Age 11
(Pigeon 1964)
Children are presented with an example set of four words that were lined logically, semantically or phonologically. The child is then presented with another set of three words, and asked to fill in the missing item from a choice of five alternatives.
BAS II Verbal Similarities Test Age 11 (Elliot et al., 1997) A series of questions where three linked items are read out to the child by the interviewer. The child is then asked to describe the main link between them. The test is designed to measure the child’s ability to identify and describe similarities between items.
British Cohort Study Millennium Cohort Study
English Picture Vocabulary Test
Age 5 (Brimer and Dunn 1962)
Children are presented with 56 sets of four pictures with a particular word associated with each of the four pictures. The child must indicate the one picture that
corresponds to the given word. BAS Naming Vocabulary Age 5 Elliott et al., (1979)
The child is shown 36 pictures of objects and is asked to name them e.g. a picture of a shoe, chair or a pair of scissors. The number of items
answered depends on his/her performance, and therefore the scores are scaled.
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The first set of cognitive tests I considered for cross-cohort comparison were measures of maths ability at age 7. In the NCDS, this was measured by the Problem Arithmetic Test (Pringle et al., 1966), while in the MCS, this was measured by the Progress in Maths Test. Both measures contain individual items chosen from the National Foundation of Education Research. Comparing the distributions of the different measures showed both to be relatively normally distributed, and therefore the two measures were considered for comparison.
The second set of cognitive tests I considered for comparison were measures of reading ability at age 7 in the NCDS and MCS. In the NCDS, this was measured by the Southgate Reading Test (Southgate 1962), while in the MCS, this was measured by the British Ability Scale (BAS) Word Reading sub-scale (Elliott et al., 1997). Although the BAS Word Reading sub-scale was shown to be relatively normally distributed, the Southgate Reading Test was shown to be extremely negatively skewed, as displayed in Figure 4.5.
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As argued by Shepherd (2012), this skewness was almost certainly due to the test being originally designed to differentiate ‘backward’ readers. Therefore, the test was unable to extend the above average reader at this age, and consequently has a low ceiling. Due to the skewness of the distribution, the Southgate Reading Test was not considered appropriate for comparison across cohorts.
The third set of the generally comparable tests I considered were measures of verbal ability at age 11. In the NCDS, this was measured by the Verbal Subset of the General Ability Test (Pigeon 1964), while in the MCS this was measured by the BAS Verbal Similarities sub-scale (Elliott et al., 1997). A comparison of the distributions showed both measures to be
relatively normally distributed, and therefore the two measures were considered
appropriate for comparison. These specific measures were also used by Goisis et al,. (2017a) and Goisis et al,.(2017b) when conducting cross-cohort comparisons between the NCDS and MCS.
The final set of generally comparable tests I considered were measures of vocabulary ability at age 5 in the BCS and MCS. In the BCS, this was measured by the English Picture
Vocabulary Test (Brimer and Dunn (1962), while in the MCS this was measured by the BAS Naming Vocabulary (Elliott et al., 1997). Once more, a comparison of the distributions showed both measures to be relatively normally distributed, and therefore applicable for cross-cohort comparison.
As shown by the various cognitive tests from the NCDS and the MCS described in Table 4.2, even if the cognitive tests are generally comparable between the cohort studies, the tests were collected in different ways and on different scales. With these differences in mind, other studies comparing the cognitive tests between the different cohorts, for instance Gregg and Macmillan (2010) and Goisis et al., (2017a, 2017b), have standardised the cognitive tests to mean 0, SD 1 for cross-cohort comparison. When using the CI, I took into account the different scales from the cognitive tests through the use of the Erreygers CI (2009) rather than the standard CI, which does not take into account the bounds of the dependent variable.