Alcohol use in early and late adolescence among the Birth to Twenty cohort in Soweto, South Africa

Figures & data

Table 1. Operational definitions of variables used at Wave 1 (year 13) and Wave 2 (year 18) of the analytical sample

Variable name	Variable source	Variable operationalisation	Variable coding
Child gender	Baseline Bt20 Demographic Questionnaire	Gender of child	Male=0 Female=1
School years repeated by grade 7	Wave 1 and 2 (year 13 and 18) Adolescent Questionnaire	Total number of ‘repeat’ school years up to grade 7	No school years repeated=0 1 school year repeated=1 2 school years repeated=2
Lifetime alcohol use	Wave 1 and 2 (year 13 and 18) Adolescent Questionnaire	Ever drunk alcohol in lifetime	No=0 Yes=1
Household SES	Baseline Bt20 Demographic questionnaire	Asset index based on a list of eight assets in the baseline household. Scores for all variables were added to obtain a value from 0 to 7, and then recoded into five SES categories	Lowest=0 (0, 1, 2 assets) Low=1 (3 assets) Medium=2 (4 assets) Higher=3 (5 assets) Highest=4 (6, 7, 8 assets)
Maternal age	Baseline Bt20 Demographic Questionnaire	Continuous data recoded into age categories that are reflective of maternal age range within the sample	13–19 years=1 20–24 years=2 25–29 years=3 30–34 years=4 35–39 years=5 40–49 years=6
Maternal education	Baseline Bt20 Demographic Questionnaire	Original six categories of maternal education included	No schooling/less than grade 5 education=1 Primary=2 Secondary=3 Post-school (i.e. diploma less than 1 year; diploma 2–3 years; 3–4 year degree; masters degree; PhD; university not specified)=4
Maternal marital status	Baseline Bt20 Demographic Questionnaire	The original variable was recoded into a binary variable based on the frequency of distribution of maternal marital status in the sample	married (any definition) or living together;=1 single or not living together=0

Table 2. Socio-demographic characteristics of the analytical sample at year 13 and year 18

	Analytical sample
	Early adolescence (n=1689)		Late adolescence (n=1735)
	n	%	n	%
Child gender
Male	762	48	758	46
Female	839	52	893	54
School years repeated by grade 7^a
0	1116	74	1162	75
1	331	22	337	22
2	55	4	59	4
Lifetime alcohol use	373	22	1140	66
Household SES (wealth category)
Lowest	230	16	229	15
Low	246	17	257	17
Medium	493	34	496	33
High	304	21	310	21
Highest	194	13	203	14

^aTotals do not add up to 100% due to rounding.

Table 3. Maternal socio-demographic characteristics at the time of the birth of the Bt20 participant

	n	%
Age
13–19 years	278	18
20–24 years	468	29
25–29 years	386	24
30–34 years	285	18
35–39 years	143	9
40–49 years	34	2
Education
No schooling/less than grade 5	81	6
Primary	93	6
Secondary	1169	79
Post-school	133	9
Marital status
Not married	987	62
Married	596	38

Table 4. Bivariate logistic regression analyses of lifetime alcohol use, SES, and child and maternal socio-demographic characteristics

	Early adolescence			Late adolescence
Lifetime use of alcohol	OR	95% CI	p	OR	95% CI	p
Child gender	1			1
Male	1.507	1.187–1.914	0.001	1.397	1.139–1.714	0.001
No. of school years repeated by grade 7
0	1			1
1	2.249	0.952–5.314	0.065	1.451	0.856–2.459	0.167
2	2.518	1.039–6.100	0.041	1.443	0.824–2.528	0.199
Maternal age at birth of the child
13–19	1			1
20–24	3.544	1.051–11.94	0.041	1.222	0.588–2.539	0.591
25–29	3.063	0.918–10.21	0.069	0.958	0.471–1.948	0.906
30–34	3.007	0.898–10.07	0.074	1.115	0.546–2.276	0.765
35–39	2.361	0.695–8.012	0.168	1.103	0.532–2.288	0.793
40–49	2.316	0.658–8.158	0.191	1.158	0.539–2.490	0.707
Maternal education at birth of the child
No schooling/less than grade 5	1			1
Primary	0.237	0.105–0.537	0.001	0.308	0.103–0.921	0.035
Secondary	0.594	0.321–1.098	0.097	0.369	0.220–0.617	0.000
Post-school	0.608	0.411–0.898	0.012	0.473	0.307–0.730	0.001
Maternal marital status at birth of the child
Not married	1			1
Married	1.047	0.818–1.340	0.716	0.726	0.587–0.897	0.003
Household SES
Lowest	1			1
Low	0.601	0.384–0.940	0.026	0.793	0.432–0.975	0.037
Medium	0.553	0.354–0.863	0.009	0.853	0.455–1.008	0.055
High	0.682	0.469–0.993	0.046	0.652	0.382–0.777	0.001
Highest	0.693	0.460–1.044	0.079	1.131	0.665–1.459	0.940

Table 5. Multivariate regression analyses of lifetime alcohol use and child and maternal socio-demographic characteristics

	Early adolescence			Late adolescence
Lifetime use of alcohol	OR	95% CI	p	OR	95% CI	p
Child gender	1			1
Male	1.372	1.054–1.786	0.019	1.387	1.103–1.745	0.005
No. of school years repeated by grade 7
0	1			1
1	2.261	0.872–5.861	0.093	1.335	0.737–2.418	0.341
2	2.489	0.872–5.861	0.067	0.489	0.737–2.418	0.341
Maternal age at birth of the child
13–19	1			1
20–24	3.966	0.872–18.026	0.075	1.040	0.428–2.526	0.931
25–29	3.623	0.811–16.178	0.092	0.682	0.289–1.608	0.382
30–34	3.225	0.726–14.323	0.124	0.778	0.332–1.821	0.563
35–39	2.436	0.543–10.927	0.245	0.741	0.313–1.759	0.497
40–49	2.211	0.475–10.306	0.312	0.745	0.304–1.825	0.519
Maternal education at birth of the child
No schooling/less than grade 5	1			1
Primary	0.312	0.127–0.768	0.011	0.381	0.106–1.368	0.139
Secondary	0.771	0.394–1.510	0.449	0.360	0.204–0.633	0.001
Post-school	0.596	0.387–0.920	0.019	0.488	0.306–0.778	0.003
Maternal marital status at birth of the child
Not married	1			1
Married	0.984	0.798–1.349	0.922	0.684	0.498–0.844	0.001
Household SES
Lowest	1			1
Low	0.681	0.417–1.112	0.125	0.837	0.535–1.309	0.435
Medium	0.596	0.366–.970	0.037	0.897	0.579–1.389	0.627
Higher	0.672	0.445–1.016	0.059	0.653	0.443–0.963	0.032
Highest	0.728	0.467–1.135	0.161	1.23	0.803–1.893	0.339