Supplementary Online Resource

Article Title: “Parental smoking during pregnancy and offspring bone mass at age 10 years: findings from a prospective birth cohort”

Journal: Osteoporosis International

Authors: Corrie Macdonald-Wallis1, Jon H Tobias2, George Davey Smith1, Debbie A Lawlor1

1 MRC Centre for Causal Analyses in Translational Epidemiology, Department of Social Medicine, University of Bristol, UK

2 Academic Rheumatology, Clinical Science at North Bristol, University of Bristol, UK

Correspondence:

Description of the multivariate multiple imputation analysis:

We imputed missing data for all children who attended the 9 year clinic for use in analysis with TBLH bone outcomes (N = 7121), while for spinal bone analysis missing data was only imputed for children whose spinal image showed only minor curvature (N = 5487). This was because the multiple imputation procedure assumes that data are either missing completely at random (MCAR) or missing at random (MAR) and there is a possibility that including children with malaligned spines in the analysis with spinal bone outcomes would violate this assumption. To impute missing data we used 10 cycles of switching regression in Stata, which has been described by Royston[1], to produce 10 full datasetseach for the TBLH and spinal bone analyses. Web-Table 1 provides details of the variables used in prediction models to impute missing data and how the models were formed. All exposures, outcomes and other variables to be used in the regression analysis were included in prediction models except TBLH and spine ABMC since these had been derived byregressing TBLH and spine BMC on BA respectively. These variables were later re-derived for each of the multiply imputed datasets. TBLH and spine BMD were passively imputed from BMC and BA at the corresponding regions since BMD is equal to BMC/BA and were not used in prediction models for these variables. To obtain our results for the main analyses, model coefficients were averaged over the 10 imputed datasets, using Rubin’s rules to produce standard errors which accounted for the uncertainty in the imputation of missing data[1]. Due to evidence of interactions of sex with both maternal and paternal smoking in regression models, we ran the multiple imputation procedure separately for male and female offspring

.

Web-Table 1 Description of variables used for multivariate multiple imputation of missing data

Variable / Type of variable / Model used to predict missing data in this variable / How variable was entered in models to predict missing data in other variables / Used in imputation of data for TBLH bone analysis, spinal bone analysis or both?
Age at DXA scan / Continuous / Linear regression / Continuous / TBLH and spine
Sex / Binary / No missing data / Binary / TBLH and spine
Height at DXA scan / Continuous / Linear regression / Continuous / TBLH and spine
Weight at DXA scan / Continuous / Linear regression / Continuous / TBLH and spine
TBLH BMC / Continuous / Linear regression / Continuous / TBLH only
TBLH BA / Continuous / Linear regression / Continuous / TBLH only
TBLH BMD / Continuous / Linear regression / Continuous / TBLH only
Spine BMC / Continuous / No missing data / Continuous / Spine only
Spine BA / Continuous / No missing data / Continuous / Spine only
Spine BMD / Continuous / No missing data / Continuous / Spine only
Gestational age / Continuous / No missing data / Continuous / TBLH and spine
Birth weight / Continuous / Linear regression / Continuous / TBLH and spine
Household social class / Ordered categorical (5 categories) / Ordinal logistic regression / 4 indicator variables / TBLH and spine
Maternal age / Continuous / No missing data / Continuous / TBLH and spine
Maternal height / Continous / Linear regression / Continuous / TBLH and spine
Maternal BMI / Continuous / Linear regression / Continuous / TBLH and spine
Maternal parity / Ordered categorical
(5 categories) / Ordinal logistic regression / 4 indicator variables / TBLH and spine
Maternal smoking during pregnancy / Ordered categorical (3 categories) / Ordinal logistic regression / 2 indicator variables / TBLH and spine
Maternal education / Ordered categorical (5 categories) / Ordinal logistic regression / 4 indicator variables / TBLH and spine
Paternal age / Continuous / Linear regression / Continuous / TBLH and spine
Paternal height / Continuous / Linear regression / Continuous / TBLH and spine
Paternal weight / Continuous / Linear regression / Continuous / TBLH and spine
Paternal smoking / Binary / Ordinal logistic regression / Binary / TBLH and spine
Paternal education / Ordered categorical (5 categories) / Ordinal logistic regression / 4 indicator variables / TBLH and spine

Abbreviations: ABMC, area-adjusted bone mineral content; BA, bone area; BMC, bone mineral content; BMD, bone mineral density; TBLH, total body less head

Web-Table 2Mean differences or odds ratios for maternal and child characteristics between mothers who smoked in any trimester and mothers who never smoked during pregnancy

Characteristic / Mean difference or odds ratio / 95% confidence interval / Pvalue
Mean differences (smoked in any trimester – never smoked)
Maternal age (yrs)
Maternal height (cm)
Maternal BMI (kg/m2)
Child’s age at DXA (yrs)
Child’s height at DXA (cm)
Child’s weight at DXA (kg)
Child’s gestational age (weeks)
Child’s birth weight (kg)
Log of child’s fat mass at DXA (g)
Odds ratios (smoked in any trimester / never smoked)
Parity: primiparous
Household social class:manual
Maternal education:A level or above / -2.07
-0.67
-0.02
0.84
-0.25
1.11
-0.06
-0.15
0.08
0.91
2.85
0.38 / -2.34, -1.80
-1.08, -0.27
-0.25, 0.22
0.61, 1.07
-0.62, 0.13
0.67, 1.55
-0.17, 0.04
-0.18, -0.12
0.05, 0.12
0.80, 1.02
2.44, 3.33
0.33, 0.43 / <0.001
0.001
0.884
<0.001
0.202
<0.001
0.249
<0.001
<0.001
0.108
<0.001
<0.001

Web-Table 3 Correlation matrix for total body less head and spinal bone measurements of the children who underwent DXA scans at age 9.9 years (Pearson correlation coefficients)

Total body BMC / Total body BA / Total body BMD / Total body ABMC / Spine BMC / Spine
BA / Spine
BMD / Spine ABMC
Total body BMC
Total body BA
Total body BMD
Total body ABMC
Spine BMC
Spine BA
Spine BMD
Spine ABMC / 1
0.976**
0.895**
0.209**
0.911**
0.797**
0.812**
0.443** / 1
0.786**
-0.008
0.897**
0.833**
0.749**
0.340** / 1
0.584**
0.800**
0.619**
0.819**
0.551** / 1
0.160**
-0.078**
0.372**
0.512** / 1
0.894**
0.869**
0.449** / 1
0.564**
0.000 / 1
0.814** / 1

* Pvalue < 0.05

**Pvalue < 0.0001

Web-Table 4 Correlations of child and parental characteristics with total body less head and spinal bone outcomes for children who underwent DXA scans at age 9.9 years (Pearson correlation coefficients shown for all except marked variables)

Total body BMC / Total body BA / Total body BMD / Total body ABMC / Spine BMC / Spine
BA / Spine
BMD / Spine ABMC
Age at DXA scan
Height at DXA scan
Weight at DXA scana
Birth weight
Gestational age
Maternal age
Maternal height
Maternal BMIa
Paternal age
Paternal height
Paternal BMIa / 0.234**
0.797**
0.823**
0.197**
0.033*
-0.002
0.229**
0.169**
0.018
0.196**
0.193** / 0.235**
0.843**
0.842**
0.216**
0.029*
-0.002
0.262**
0.165**
0.017
0.229**
0.194** / 0.185**
0.599**
0.662**
0.139**
0.038*
-0.001
0.136**
0.151**
0.015
0.105**
0.165** / 0.012
-0.127**
-0.037*
-0.065**
0.020
-0.002
-0.127**
0.024
0.004
-0.136**
0.000 / 0.186**
0.728**
0.772**
0.158**
0.012
0.013
0.216**
0.165**
0.025
0.197**
0.185** / 0.190**
0.787**
0.745**
0.185**
-0.002
0.013
0.262**
0.139**
0.025
0.247**
0.164** / 0.132**
0.493**
0.604**
0.095**
0.026
0.011
0.118**
0.157**
0.022
0.094**
0.169** / 0.038*
0.055**
0.182**
-0.017
0.030*
0.002
-0.043*
0.096**
0.007
-0.061*
0.085**

* Pvalue < 0.05

**Pvalue < 0.0001

a Spearman correlation coefficients used due to skewed variables

Web-Table 5 Sex-specific associations of maternal and paternal smoking with total body less head bone outcomes at age 9.9 years in complete case analysis (boys N = 1668; girls N = 1699)

Boys / TBLH BMC
(SD score: 1 SD = 175.6g) / TBLH BA
(SD score: 1 SD = 155.7cm2) / TBLH BMD
(SD score: 1 SD = 0.053g/cm2)
Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value
Maternal smoking in any trimester
Model 1
Model 2
Model 3 / -0.02
0.04
0.00 / -0.14, 0.10
-0.08, 0.16
-0.06, 0.07 / 0.748
0.497
0.969 / -0.01
0.06
0.02 / -0.13, 0.11
-0.06, 0.18
-0.03, 0.08 / 0.886
0.299
0.358 / -0.03
0.01
-0.03 / -0.15, 0.10
-0.12, 0.13
-0.13, 0.08 / 0.667
0.906
0.608
Maternal smoking in all trimesters
Model 1
Model 2
Model 3 / 0.05
0.12
-0.04 / -0.11, 0.21
-0.04, 0.28
-0.12, 0.05 / 0.545
0.133
0.394 / 0.07
0.16
0.00 / -0.08, 0.23
0.00, 0.32
-0.07, 0.07 / 0.357
0.047
0.953 / 0.01
0.05
-0.07 / -0.16, 0.17
-0.12, 0.22
-0.21, 0.06 / 0.926
0.561
0.280
Paternal smoking
Model 1
Model 2
Model 3 / 0.02
0.03
0.01 / -0.08, 0.11
-0.07, 0.12
-0.04, 0.06 / 0.749
0.596
0.594 / 0.02
0.04
0.03 / -0.07, 0.12
-0.06, 0.13
-0.02, 0.07 / 0.616
0.453
0.236 / 0.00
0.01
0.00 / -0.10, 0.10
-0.09, 0.11
-0.08, 0.08 / 0.989
0.896
0.921
Combined models / -0.01
0.02
0.04
0.01
-0.00
0.02 / -0.14, 0.11
-0.08, 0.12
-0.08, 0.17
-0.08, 0.11
-0.07, 0.07
-0.04, 0.07 / 0.819
0.641
0.503
0.769
0.922
0.536 / 0.00
0.03
0.06
0.02
0.02
0.02 / -0.13, 0.12
-0.07, 0.13
-0.06, 0.18
-0.08, 0.11
-0.04, 0.07
-0.02, 0.07 / 0.952
0.553
0.312
0.696
0.520
0.317 / -0.02
0.01
0.01
0.00
-0.03
0.01 / -0.15, 0.11
-0.09, 0.11
-0.12, 0.15
-0.10, 0.11
-0.13, 0.08
-0.08, 0.09 / 0.762
0.853
0.857
0.927
0.645
0.893
Model 1
Model 2
Model 3 / Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Girls / TBLH BMC
(SD score: 1 SD = 191.0g) / TBLH BA
(SD score: 1 SD = 171.7cm2) / TBLH BMD
(SD score: 1 SD = 0.055g/cm2)
Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value
Maternal smoking in any trimester
Model 1
Model 2
Model 3 / 0.12
0.14
0.00 / -0.00, 0.24
0.02, 0.26
-0.05, 0.06 / 0.053
0.022
0.893 / 0.11
0.13
0.00 / -0.01, 0.22
0.01, 0.25
-0.05, 0.05 / 0.082
0.030
0.933 / 0.13
0.14
0.02 / 0.00, 0.26
0.01, 0.27
-0.07, 0.12 / 0.046
0.031
0.652
Maternal smoking in all trimesters
Model 1
Model 2
Model 3 / 0.15
0.20
0.03 / 0.01, 0.30
0.05, 0.34
-0.04, 0.10 / 0.037
0.008
0.334 / 0.13
0.18
0.02 / -0.01, 0.27
0.04, 0.32
-0.04, 0.08 / 0.077
0.014
0.470 / 0.17
0.19
0.05 / 0.02, 0.33
0.04, 0.35
-0.06, 0.17 / 0.028
0.015
0.376
Paternal smoking
Model 1
Model 2
Model 3 / 0.10
0.10
0.03 / 0.01, 0.20
0.01, 0.19
-0.01, 0.08 / 0.033
0.037
0.163 / 0.10
0.09
0.03 / 0.00, 0.19
-0.00, 0.19
-0.01, 0.06 / 0.045
0.051
0.166 / 0.10
0.10
0.04 / 0.00, 0.20
0.00, 0.20
-0.03, 0.11 / 0.040
0.043
0.264
Combined models / 0.10
0.07
0.12
0.07
-0.01
0.03 / -0.02, 0.23
-0.03, 0.17
-0.00, 0.24
-0.03, 0.16
-0.07, 0.05
-0.02, 0.08 / 0.095
0.150
0.051
0.182
0.832
0.193 / 0.09
0.07
0.11
0.06
-0.01
0.03 / -0.03, 0.21
-0.03, 0.16
-0.01, 0.23
-0.03, 0.15
-0.06, 0.04
-0.01, 0.07 / 0.130
0.161
0.061
0.204
0.652
0.168 / 0.11
0.07
0.12
0.07
0.01
0.04 / -0.02, 0.24
-0.04, 0.17
-0.01, 0.25
-0.04, 0.17
-0.09, 0.11
-0.04, 0.11 / 0.093
0.202
0.073
0.215
0.848
0.365
Model 1
Model 2
Model 3 / Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking

Abbreviations: BA, bone area; BMC, bone mineral content; BMD, bone mineral density; TBLH, total body less head

Model 1 is adjusted for the child’s age, mother’s parity, household social class and maternal/paternal factors (age, height, pre-pregnancy BMI, education).

Model 2 is adjusted additionally for the child’s gestational age and birth weight.

Model 3 is adjusted for all these plus the child’s height and weight at 9.9 years.

a Maternal smoking in any trimester.

Reference category for maternal smoking variables is “Never smoked during pregnancy” and for paternal smoking variable is “Non-smoking”

Web-Table 6Sex-specific associations of maternal and paternal smoking with spinal bone outcomes at age 9.9 years for complete case analysis (boys N = 1372; girls N = 1320)

Boys / Spine BMC
(SD score: 1 SD = 14.8g) / Spine BA
(SD score: 1 SD = 11.7cm2) / Spine BMD
(SD score: 1 SD = 0.076g/cm2)
Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value
Maternal smoking in any trimester
Model 1
Model 2
Model 3 / 0.05
0.11
0.06 / -0.08, 0.19
-0.03, 0.24
-0.03, 0.15 / 0.451
0.121
0.174 / 0.05
0.12
0.09 / -0.08, 0.19
-0.02, 0.25
0.00, 0.17 / 0.440
0.088
0.048 / 0.03
0.07
0.02 / -0.11, 0.17
-0.08, 0.21
-0.10, 0.14 / 0.636
0.362
0.739
Maternal smoking in all trimesters
Model 1
Model 2
Model 3 / 0.09
0.16
-0.02 / -0.09, 0.27
-0.02, 0.33
-0.14, 0.10 / 0.328
0.090
0.736 / 0.13
0.20
0.04 / -0.06, 0.31
0.02, 0.38
-0.08, 0.15 / 0.174
0.027
0.526 / 0.02
0.06
-0.08 / -0.16, 0.21
-0.13, 0.25
-0.24, 0.08 / 0.814
0.526
0.351
Paternal smoking
Model 1
Model 2
Model 3 / 0.01
0.02
0.03 / -0.10, 0.12
-0.08, 0.13
-0.04, 0.10 / 0.802
0.662
0.444 / 0.02
0.03
0.04 / -0.09, 0.13
-0.08, 0.14
-0.03, 0.10 / 0.751
0.595
0.284 / 0.00
0.01
0.01 / -0.11, 0.12
-0.10, 0.12
-0.09, 0.10 / 0.973
0.888
0.893
Combined models / 0.08
-0.02
0.13
-0.02
0.06
0.01 / -0.06, 0.22
-0.13, 0.10
-0.01, 0.27
-0.13, 0.09
-0.03, 0.16
-0.07, 0.08 / 0.251
0.792
0.067
0.696
0.200
0.818 / 0.08
-0.02
0.14
-0.03
0.09
0.01 / -0.06, 0.23
-0.13, 0.09
0.00, 0.28
-0.14, 0.08
-0.00, 0.18
-0.07, 0.08 / 0.238
0.758
0.046
0.646
0.057
0.854 / 0.06
-0.01
0.09
-0.02
0.02
0.00 / -0.09, 0.21
-0.13, 0.11
-0.06, 0.24
-0.13, 0.10
-0.11, 0.15
-0.10, 0.11 / 0.446
0.843
0.257
0.790
0.736
0.924
Model 1
Model 2
Model 3 / Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Girls / Spine BMC
(SD score: 1 SD = 16.7g) / Spine BA
(SD score: 1 SD = 12.3cm2) / Spine BMD
(SD score: 1 SD = 0.086g/cm2)
Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value / Mean difference / 95% CI / P
value
Maternal smoking in any trimester
Model 1
Model 2
Model 3 / 0.13
0.15
0.00 / -0.01, 0.27
0.01, 0.28
-0.08, 0.08 / 0.066
0.037
0.986 / 0.13
0.15
0.03 / -0.01, 0.27
0.02, 0.29
-0.05, 0.12 / 0.068
0.029
0.415 / 0.11
0.12
-0.02 / -0.03, 0.25
-0.03, 0.26
-0.13, 0.09 / 0.126
0.109
0.710
Maternal smoking in all trimesters
Model 1
Model 2
Model 3 / 0.12
0.16
0.02 / -0.04, 0.29
-0.01, 0.33
-0.08, 0.12 / 0.151
0.061
0.706 / 0.08
0.13
0.03 / -0.09, 0.25
-0.04, 0.30
-0.07, 0.13 / 0.351
0.120
0.554 / 0.15
0.16
0.02 / -0.03, 0.33
-0.01, 0.34
-0.12, 0.16 / 0.093
0.069
0.815
Paternal smoking
Model 1
Model 2
Model 3 / 0.05
0.04
-0.03 / -0.06, 0.16
-0.07, 0.15
-0.09, 0.04 / 0.412
0.464
0.374 / 0.01
0.01
-0.05 / -0.10, 0.13
-0.10, 0.12
-0.11, 0.02 / 0.792
0.899
0.140 / 0.08
0.08
0.01 / -0.04, 0.19
-0.04, 0.19
-0.08, 0.10 / 0.181
0.188
0.859
Combined models / 0.14
-0.01
0.15
-0.01
0.01
-0.03 / 0.00, 0.28
-0.12, 0.10
0.01, 0.29
-0.13, 0.10
-0.07, 0.10
-0.10, 0.04 / 0.050
0.878
0.030
0.802
0.799
0.357 / 0.16
-0.05
0.18
-0.06
0.06
-0.07 / 0.02, 0.30
-0.16, 0.07
0.04, 0.32
-0.17, 0.06
-0.03, 0.14
-0.14, 0.00 / 0.028
0.415
0.012
0.324
0.181
0.051 / 0.10
0.04
0.11
0.04
-0.03
0.02 / -0.05, 0.25
-0.08, 0.16
-0.04, 0.25
-0.08, 0.16
-0.15, 0.09
-0.08, 0.11 / 0.181
0.528
0.166
0.531
0.625
0.700
Model 1
Model 2
Model 3 / Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking
Maternal smokinga
Paternal smoking

Abbreviations: BA, bone area; BMC, bone mineral content; BMD, bone mineral density

Model 1 is adjusted for the child’s age, mother’s parity, household social class and maternal/paternal factors (age, height, pre-pregnancy BMI, education).

Model 2 is adjusted additionally for the child’s gestational age and birth weight.

Model 3 is adjusted for all these plus the child’s height and weight at 9.9 years.

a Maternal smoking in any trimester.

Reference category for maternal smoking variables is “Never smoked during pregnancy” and for paternal smoking variable is “Non-smoking”

Web-Table 7 Distributions of child and parental variables in multiply imputed and complete case datasets for total body less head bone outcome analysis

Characteristic / Imputed datasets
Mean (SE) or % / Complete case dataset
Mean (SE) or %
Child
Age at DXA scan (months) / 118.4 (0.05) / 118.1 (0.06)
Sex / Male
Female / 49.6
50.4 / 49.5
50.5
Height (cm) / 139.5 (0.07) / 139.6 (0.11)
Weight (kg) / 34.7 (0.09) / 34.5 (0.12)
TBLH BMC (g) / 893.5 (2.2) / 889.5 (3.1)
TBLH BA (cm2) / 1139.1 (2.0) / 1135.8 (2.8)
TBLH BMD (g/cm2) / 0.78 (0.00) / 0.78 (0.00)
TBLH ABMC / 893.5 (0.52) / 894.5 (0.67)
Gestational age (wks) / 39.5 (0.02) / 39.6 (0.03)
Birth weight (kg) / 3.4 (0.00) / 3.5 (0.00)
Household social class / I
II
III NM
III M
IV/V / 15.0
44.4
25.2
10.8
4.6 / 18.5
48.2
23.0
7.3
3.1
Mother
Age at delivery (yrs) / 29.0 (0.05) / 29.4 (0.07)
Height (cm) / 164.1 (0.08) / 164.3 (0.11)
Pre-pregnancy BMI (kg/m2) / 22.9 (0.05) / 22.9 (0.06)
Parity / 0
1
2
3
4 or more / 46.0
35.4
13.7
3.8
1.2 / 49.0
35.1
12.2
3.1
0.6
Smoking during pregnancy / Never
1 or 2 trimesters
All trimesters / 78.6
9.6
11.8 / 84.2
6.6
9.2
Education / None/CSE
Vocational
O Levels
A Levels
Degree / 14.1
8.6
35.2
26.4
15.7 / 8.9
7.3
35.7
28.2
19.9
Father
Age at child’s birth (yrs) / 31.3 (0.07) / 31.5 (0.09)
Height (cm) / 176.1 (0.11) / 176.5 (0.12)
BMI (kg/m2) / 25.2 (0.04) / 25.2 (0.06)
Regular smoker / No
Yes / 64.6
35.4 / 69.2
30.8
Education / None/CSE
Vocational
O Levels
A Levels
Degree / 20.4
8.4
21.8
28.1
21.4 / 14.0
7.5
21.7
29.8
27.1

Web-Table 8 Distributions of child and parental variables in multiply imputed and complete case datasets for spinal bone outcome analysis

Characteristic / Imputed datasets
Mean (SE) or % / Complete Case
Mean (SE) or %
Child
Age at DXA scan (months) / 118.5 (0.05) / 118.1 (0.07)
Sex / Male
Female / 50.5
49.5 / 51.0
49.0
Height (cm) / 139.4 (0.09) / 139.5 (0.12)
Weight (kg) / 34.8 (0.10) / 34.5 (0.14)
Spine BMC (g) / 78.4 (0.21) / 78.3 (0.30)
Spine BA (cm2) / 100.7 (0.16) / 100.8 (0.23)
Spine BMD (g/cm2) / 0.77 (0.00) / 0.77 (0.00)
Spine ABMC / 78.4 (0.10) / 78.2 (0.14)
Gestational age (wks) / 39.5 (0.02) / 39.6 (0.03)
Birth weight (kg) / 3.4 (0.00) / 3.5 (0.00)
Household social class / I
II
III NM
III M
IV/V / 14.8
44.6
24.9
11.1
4.6 / 18.7
47.8
23.0
7.5
3.0
Mother
Age at delivery (yrs) / 29.0 (0.06) / 29.3 (0.08)
Height (cm) / 164.0 (0.09) / 164.2 (0.13)
Pre-pregnancy BMI (kg/m2) / 23.0 (0.05) / 23.0 (0.07)
Parity / 0
1
2
3
4 or more / 46.0
35.3
13.6
3.9
1.2 / 48.9
35.1
12.1
3.4
0.6
Smoking during pregnancy / Never
1 or 2 trimesters
All trimesters / 78.3
9.9
11.8 / 83.8
7.0
9.2
Education / None/CSE
Vocational
O Levels
A Levels
Degree / 13.8
8.5
35.3
26.9
15.5 / 9.0
7.6
35.3
28.4
19.8
Father
Age at child’s birth (yrs) / 31.2 (0.08) / 31.4 (0.10)
Height (cm) / 176.0 (0.10) / 176.3 (0.13)
BMI (kg/m2) / 25.2 (0.05) / 25.2 (0.06)
Regular smoker / No
Yes / 64.3
35.7 / 69.2
30.8
Education / None/CSE
Vocational
O Levels
A Levels
Degree / 20.2
8.4
22.2
27.9
21.3 / 13.8
7.4
22.3
29.6
26.9

Reference List

1Royston P. Multiple imputation of missing values. Stata Journal 2004; 4: 227-41