First, I analysed the relationship between SES and the child cognitive assessments in the NCDS, utilising OLS regression models and parental occupational classification as a broad measure of SES. Tables 4.11 and 4.12 show a summary of the results from OLS models for the cognitive assessments at ages 7 and 11 respectively. In the interests of space, full regression output is presented in Appendix 4D.
The results from Table 4.11 and 4.12 show that there were significant socioeconomic inequalities in child cognitive ability across all cognitive tests at both 7 and 11 in the NCDS, with those children whose fathers were in the lowest occupational classification having a disadvantage of between 0.4 to 0.9 SD compared to those cohort children whose fathers were in the highest occupational classification. Goodman et al., (2015) have suggested that, in the context of child development, any effect size over 0.1 SD can be considered
economically significant, and therefore these differences can be considered relatively
substantial. In general, the magnitude of these inequalities was larger at age 11 compared to age 7, implying that socioeconomic inequalities in cognitive ability may have increased over childhood, with this in line with the findings of several prominent studies, including Feinstein (2003). The exception to this general trend was the measure of copying ability, which
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Table 4.11- Relationship between SES measured by parental occupation and child cognitive ability (NCDS Age 7)
(1) (2) (3) (4)
Reading Maths Drawing Copying Parental Social Class
I (Omitted) (Omitted) (Omitted) (Omitted) II -0.116*** (0.032) -0.172*** (0.045) -0.094* (0.049) -0.088** (0.044) III -0.316*** (0.030) -0.366*** (0.041) -0.218*** (0.046) -0.213*** (0.040) IV -0.461*** (0.037) -0.465*** (0.046) -0.309*** (0.050) -0.277*** (0.045) V -0.663*** (0.050) -0.545*** (0.056) -0.411*** (0.059) -0.405*** (0.056) Observations 10921 10921 10921 10921 R-squared 0.149 0.066 0.054 0.059
Notes: Summary of empirical estimates. Full regression output available in Appendix 4D. Robust standard errors in parentheses. *** Significant at 1%, ** at 5%, * at 10%.
Table 4.12- Relationship between SES measured by parental occupation and child cognitive ability (NCDS Age 11)
(1) (2) (3) (4) (5) Verbal Non-Verbal Maths Reading Copying Parental Social Class
I (Omitted) (Omitted) (Omitted) (Omitted) (Omitted) II -0.186*** (0.041) -0.204*** (0.042) -0.214*** (0.045) -0.181*** (0.044) -0.096* (0.051) III -0.452*** (0.038) -0.470*** (0.039) -0.562*** (0.042) -0.499*** (0.041) -0.203*** (0.048) IV -0.590*** (0.043) -0.593*** (0.044) -0.730*** (0.046) -0.633*** (0.045) -0.275*** (0.053) V -0.796*** (0.054) -0.839*** (0.054) -0.901*** (0.054) -0.805*** (0.056) -0.403*** (0.064) Observations 9900 9900 9900 9900 9900 R-squared 0.159 0.155 0.181 0.191 0.041
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As shown in Appendix 4D, in general the other explanatory variables included in models had the signs and magnitude expected given the previous empirical and theoretical literature. For example, years of maternal education, maternal employment, maternal age, levels of breastfeeding and being white were positively associated with child cognitive ability, whilst smoking during pregnancy, an increased family size, being a preterm birth and having a low birth weight were all associated with decreased levels of cognitive ability. The effect of gender differed depending on the cognitive test in question, with boys having the advantage in maths and copying, while girls on average having higher levels of reading, drawing and verbal ability.
The additional results displayed in Table 4.13 show that these estimates were robust to the exclusion of the ethnicity variable, with very marginal differences in the magnitude of the coefficients and no difference in the level of statistical significance when the ethnicity variable was excluded from empirical analysis.
Table 4.13- Relationship between SES measured by parental occupation and child cognitive ability with the ethnicity variable excluded (NCDS Age 7)
(1) (2) (3) (4) Reading Maths Drawing Copying Parental Social
Class
I (Omitted) (Omitted) (Omitted) (Omitted) II -0.110*** (0.031) -0.140*** (0.043) -0.077* (0.046) -0.089** (0.041) III -0.316*** (0.029) -0.340*** (0.039) -0.201*** (0.043) -0.212*** (0.038) IV -0.474*** (0.035) -0.456*** (0.043) -0.305*** (0.047) -0.282*** (0.042) V -0.678*** (0.047) -0.553*** (0.053) -0.410*** (0.055) -0.413*** (0.052) Observations 12545 12545 12545 12545 R-squared 0.151 0.066 0.054 0.055
Notes: Summary of empirical estimates. Robust standard errors in parentheses. *** Significant at 1%, ** at 5%, * at 10%.
The results displayed in Appendix 4E show that the inclusion of IPWs used to control for missing data in general marginally decreased the extent of socioeconomic inequality, therefore implying the associations presented in this section may be considered an upper bound of the true estimate.
Next, I estimated the relationship between SES and child cognitive ability in the BCS, using OLS regression models and parental occupational classification as the measure of SES. Tables 4.14 and 4.15 show the relationship between SES and child cognitive ability using OLS
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models at the ages of 5 and 10 respectively. In the interests of space, full regression output is presented in Appendix 4F.
Significant socioeconomic inequalities in child cognitive ability were shown for most of the cognitive tests across both age groups, with those children whose fathers are in the lowest occupational classification having a disadvantage of between 0.2 to 0.7 SD, compared to those whose fathers are in the highest occupational classification. The one exception to this pattern was the BAS Digits cognitive test, which showed smaller differences between
socioeconomic groups, with these differences also not found to be statistically significant. In general there was less evidence of a widening of socioeconomic inequalities over time compared to the results from the NCDS. However, it was difficult to fully investigate any changes over time because of the lack of comparability between the measures of cognitive ability at the ages of 5 and 10 in this cohort study.
As shown in Appendix 4F, the other explanatory variables included in the model specifications had the sign and magnitude expected given the previous theoretical and empirical literature, with positive associations between cognitive ability and maternal
factors such as education, age, employment and breastfeeding, and negative associations for factors such as family size and smoking during pregnancy. There were also significant gender disparities depending on the cognitive test, with males having advantages in cognitive tests such as vocabulary and the matrices subset of the BAS, and females having advantages in cognitive scores such as drawing ability and the digits subset of the BAS. The results from Appendix 4G show that these results were also robust to the inclusion of IPWs to control for missing data.
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Table 4.14- Relationship between SES measured by parental occupation and cognitive ability (BCS Age 5)
(1) (2) (3) (4)
Drawing Copying Profile Vocabulary Parental Social Class
I (Omitted) (Omitted) (Omitted) (Omitted) II -0.055 (0.040) -0.125*** (0.046) -0.049 (0.050) -0.160*** (0.051) III -0.147*** (0.035) -0.286*** (0.041) -0.132*** (0.045) -0.215*** (0.045) IV -0.190*** (0.041) -0.400*** (0.047) -0.154*** (0.051) -0.349*** (0.051) V -0.301*** (0.049) -0.541*** (0.056) -0.317*** (0.059) -0.582*** (0.062) Observations 11167 11167 11167 8616 R-squared 0.042 0.101 0.018 0.134
Notes: Summary of empirical estimates Full output available in Appendix 4F. Robust standard errors in parentheses. *** Significant at 1%, ** at 5%, * at 10%.
Table 4.15- Relationship between SES measured by parental occupation and cognitive ability (BCS Age 10)
(1) (2) (3) (4) (5) (6) (7) (8) Maths Reading Definitions Digits Similarities Matrices Spelling Vocabulary Social Class
I (Omitted) (Omitted) (Omitted) (Omitted) (Omitted) (Omitted) (Omitted) (Omitted) II -0.300*** (0.047) -0.233*** (0.043) -0.138** (0.061) 0.009 (0.057) 0.023 (0.058) -0.011 (0.060) -0.010 (0.060) 0.008 (0.060) III -0.558*** (0.042) -0.455*** (0.038) -0.332*** (0.056) -0.022 (0.052) -0.051 (0.053) -0.112** (0.055) -0.073 (0.054) -0.078 (0.055) IV -0.676*** (0.048) -0.601*** (0.045) -0.432*** (0.059) -0.028 (0.056) -0.087 (0.057) -0.155** (0.060) -0.123** (0.060) -0.144** (0.059) V -0.854*** (0.058) -0.747*** (0.057) -0.549*** (0.065) -0.090 (0.065) -0.194*** (0.065) -0.298*** (0.070) -0.167** (0.071) -0.234** (0.067) Observations 9181 9187 10790 10790 10790 8573 8255 10790 R-squared 0.151 0.172 0.091 0.017 0.025 0.037 0.048 0.031
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Next, I estimated the relationship between SES and child cognitive ability in the MCS, using the same techniques as for the NCDS and BCS. Tables 4.16 - 4.18 show the relationship between SES measured by parental occupation and child cognitive ability, estimated by OLS models at age 5, 7 and 11 respectively. Full regression output is presented in Appendix 4H.
Table 4.16- Relationship between SES measured by parental occupation and cognitive ability (MCS Age 5)
(1) (2) (3)
Verbal Similarities Vocabulary Pattern Parental Social Class
I (Omitted) (Omitted) (Omitted) II -0.094*** (0.031) -0.166*** (0.029) -0.154*** (0.028) III -0.182*** (0.044) -0.258*** (0.036) -0.102*** (0.036) IV -0.099*** (0.037) -0.278*** (0.034) -0.189*** (0.039) V -0.154*** (0.032) -0.335*** (0.026) -0.250*** (0.031) Observations 13592 13592 13592 R-Squared 0.056 0.185 0.076
Notes: Summary of empirical estimates. Full regression output displayed in Appendix 4H. Robust standard errors in parentheses. ***
Significant at 1%, ** at 5%, * at 10%.
Table 4.17- Relationship between SES measured by parental occupation and cognitive ability (MCS Age 7)
(1) (2) (3)
Reading Maths Pattern Parental Social
Class
I (Omitted) (Omitted) (Omitted) II -0.141*** (0.032) -0.191*** (0.032) -0.149*** (0.033) III -0.271*** (0.042) -0.232*** (0.041) -0.109*** (0.038) IV -0.323*** (0.037) -0.278*** (0.043) -0.198*** (0.040) V -0.356*** (0.031) -0.347*** (0.031) -0.293*** (0.033) Observations 12071 12071 12071 R-squared 0.134 0.094 0.085
Notes: Summary of empirical estimates. Full regression output displayed in Appendix 4H. Robust standard errors in parentheses. ***
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Table 4.18- Relationship between SES measured by parental occupation and cognitive ability (MCS Age 11)
Parental Social Class Verbal Ability
I (Omitted) II -0.131*** (0.035) III -0.233*** (0.045) IV -0.214*** (0.040) V -0.325*** (0.033) Observations 11971 R-squared 0.116
Notes: Summary of empirical estimates. Full regression output displayed in Appendix 4H. Robust standard errors in parentheses.
*** Significant at 1%, ** at 5%, * at 10%.
There was once more evidence of significant socioeconomic inequalities across all cognitive outcomes, with those children with parents in the lowest occupational classifications having a disadvantage of between 0.15 to 0.35 SD, compared to those children with parents in the highest occupational classification. Similar to the results from the BCS, there was little evidence of widening socioeconomic inequalities over time.
Examining the results presented in Appendix 4H, the other explanatory variables included in the empirical models had the sign and magnitude expected given the previous theoretical and empirical literature. For instance, there were positive associations between child cognitive ability and factors such as maternal education, age and breastfeeding, and negative associations for factors such as an increased family size, low birth weights and smoking during pregnancy. Although consistently correlated with cognitive ability in the NCDS and BCS, the correlation between maternal employment and cognitive ability was smaller in the MCS compared to the other cohort studies, with these differences also not always statistically significant. There were significant gender disparities depending on the cognitive test, with females having advantages in cognitive tests such as reading ability and pattern construction. There was no evidence of differences by gender for the measure of mathematical ability. The results from Appendix 4I show that these results were also robust to the inclusion of IPWs to control for missing data.
In general, the results from the various OLS models using parental occupation as a measure of SES imply a narrowing of the level of socioeconomic inequality across time, with the average disadvantage across all the cognitive tests between the highest and lowest parental
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occupational groups (as measured by the NSSEC-5) decreasing from just over 0.6 SD in the NCDS to around 0.4 SD in the BCS and 0.3 SD in the MCS respectively.