Supplementary Material
Estimated prevalence of tobacco dependence among female smokers age 12-44 years, by pregnancy status
and pregnancy months, based on three TD case identification approaches: (1) Composite NDSS/TTFC
index; (2) NDSS index (with no consideration of Fagerstrom TTFC item); (3) Fagerstrom TTFC index
(with no consideration of NDSS).
NSDUH assess TD based on a field survey version of the Nicotine Dependence Syndrome Scale (NDSS)
and a single 'Time To First Cigarette' (TTFC) item from the Fagerstrom Test for Nicotine Dependence
(FTND) for respondents who reported smoking cigarettes in the past month. The NDSS is calculated as
the average score over 17 questions pertaining to five aspects of dependence (Shiffman et al., 2004).
Based on the NDSS score, a respondent was defined as having nicotine dependence if their average score
was greater than or equal to 2.75. Based on the FTND scale, a respondent was defined as having nicotine
dependence if the first cigarette was smoked within 30 minutes of waking up on the days they smoked.
For this research, we turned first to a composite measure of TD: either an NDSS-positive or a TTFCpositive response was sufficient for our case definition for TD in this pregnancy research. This
supplement provides estimates based on NDSS by itself (without regard to TTFC assessment) and based
on the TTFC assessment (without regard for NDSS assessment).
1
Appendix table 1: Estimated tobacco dependence prevalence for female smokers age 12-44 years, by
pregnancy status and pregnancy months, with prevalence ratios, based on composite NDSS/TTFC index.*
Data for the United States based on the R-DAS online analysis system of the National Surveys on Drug
Use and Health, 2002-2009.
Panel A
Prevalence %(95%C.I)
Prevalence ratio (95%C.I)
Non-pregnant
1-2 months
52.7 (52.0, 53.4)
60.4 (53.4, 67.1)
Referent
1.1 (1.02, 1.3)
3-7 months
68.7 (64.2, 72.9)
1.3 (1.2, 1.4)
8-9 months
65.0 (56.4, 72.7)
1.2 (1.1, 1.4)
3-9 months
67.9 (63.9, 71.7)
1.3 (1.2, 1.4)
1-2 months
60.4 (53.4, 67.1)
Referent
3-7 months
8-9 months
68.7 (64.2, 72.9)
65.0 (56.4, 72.7)
1.1 (1.0, 1.3)
1.1 (0.9, 1.3)
3-9 months
67.9 (63.9, 71.7)
1.1 (0.99, 1.3)
Panel B
* Based on composite TD index from the Nicotine Dependence Syndrome Scale and the Fagerstrom Time
To First Cigarette item, as described below in this online appendix.
2
Appendix Table 2: Estimated tobacco dependence prevalence for female smokers age 12-44 years, by
pregnancy status and pregnancy months, with prevalence ratios, based on NDSS index.** Data for the
United States based on the R-DAS online analysis system of the National Surveys on Drug Use and
Health, 2002-2009.
Panel A
Women12-44 years old
Prevalence %(95%C.I)
Prevalence ratio (95%C.I)
Non-pregnant
1-2 months
3-7 months
8-9 months
39.4 (38.7, 40.0)
42.6 (35.8, 49.6)
51.0 (46.3, 55.7)
49.2 (40.6, 57.8)
Referent
1.1 (0.9, 1.3)
1.3 (1.2, 1.4)
1.2 (1.0, 1.5)
3-9 months
50.6 (46.6, 54.7)
1.3 (1.2, 1.4)
Panel B
Women12-44 years old
1-2 months
3-7 months
8-9 months
3-9 months
Prevalence %(95%C.I)
42.6 (35.8, 49.6)
51.0 (46.3, 55.7)
49.2 (40.6, 57.8)
50.6 (46.6, 54.7)
Prevalence ratio (95%C.I)
Referent
1.2 (0.99, 1.4)
1.2 (0.9, 1.5)
1.2 (0.99, 1.4)
** Based on TD index from the Nicotine Dependence Syndrome Scale without consideration of the
Fagerstrom Time To First Cigarette item, as described below in this online appendix.
3
Appendix table 3: Estimated tobacco dependence prevalence for female smokers age 12-44 years, by
pregnancy status and pregnancy months, with prevalence ratios, based on TTFC index.*** Data for the
United States based on the R-DAS online analysis system of the National Surveys on Drug Use and
Health, 2002-2009.
Panel A
Women12-44 years old
Prevalence % (95%C.I)
Prevalence ratio (95%C.I)
Non-pregnant
42.8 (42.1, 43.5)
Referent
1-2 months
47.4 (40.7, 54.2)
1.1 (0.9, 1.3)
3-7 months
57.4 (52.6, 62.0)
1.3 (1.2, 1.5)
8-9 months
45.5 (37.2, 54.2)
1.1 (0.9, 1.3)
3-9 months
54.8 (50.5, 59.0)
1.3 (1.2, 1.4)
Panel B
Women12-44 years old
Prevalence % (95%C.I)
Prevalence ratio (95%C.I)
1-2 months
47.4 (40.7, 54.2)
Referent
3-7 months
57.4 (52.6, 62.0)
1.2 (1.03, 1.4)
8-9 months
45.5 (37.2, 54.2)
0.9 (0.8, 1.2)
3-9 months
54.8 (50.5, 59.0)
1.2(1.0, 1.4)
***Based on Fagerstrom Time To First Cigarette item (without consideration of the Nicotine Dependence
Severity Scale), as described below in this online appendix.
4
Indirect Age standardization
The newly implemented R-DAS only generates descriptive statistics in the context of contingency
tables. It does not permit use of inferential statistics such as the generalized linear model or other
regression approaches. However, it provides correct weights for aggregate analyses of the pooled 20022009 NSDUH data, as well as Taylor series linearization variance estimates from which effective
unweighted sample distributions can be derived for each contrast. This online supplement attempts to help
researchers to further utilize R-DAS in inferential statistics approach such as indirect standardization.
Crude smoking estimates can be misleading since they are not very informative about the
smoking status comparing the two groups. Standardization for the variable which may be responsible for
the observed differences is necessary. Although standardization can be applied using any suspected
confounder, age is the most common variable used for standardization. In the current study we used an
indirect age standardization approach (Breslow and Day, 1975) where we identified a referent population
(non pregnant females 12-44 years of age). We generated, using R-DAS, the observed prevalence (%) of
smoking by month of pregnancy among pregnant females 12-44 years old. We also generated, using RDAS, the age-specific smoking prevalence (%) from the reference population. We multiplied the
percentage of pregnant females in each age group (generated by R-DAS) by the age-specific smoking
prevalence (%) in the comparable age group of the reference population. We summed the total percentage
of expected smoking for each pregnancy month. We divided the overall percentage of observed smoking
by the summed ‘expected’ percentage for each pregnancy month. The ratio of the observed number of
smokers to the expected number of smokers is called: “Age standardized smoking ratio”.
5
Appendix Table 4A Illustrating Indirect Age Standardization Using Non-Pregnant Women as the Reference
Population (point estimates)
Month of
Participants (%) in
Observed
Age specific
Expected
Age
pregnancy
each age group
prevalence (%)
prevalence (%)
prevalence (%)
standardized
(A)
(O)
among non-pregnant
(E=A*B)
ratio (O/E)
(B)
1 month
12-20 years
8.3
17.9
3.3
18.6
21-30 years
47.2
11.2
34.3
16.2
31-44 years
34.2
7.1
27.5
9.4
Total
100
26.6
28.9
0.9
2 months
12-20 years
16.4
5.6
17.9
2.9
21-30 years
51.3
13.2
34.3
17.6
31-44 years
32.3
5.7
27.5
8.9
Total
100
24.5
29.4
0.8
3 months
12-20 years
17.3
5.1
17.9
3.1
21-30 years
53.8
10.6
34.3
18.5
31-44 years
28.9
1.9
27.5
7.9
Total
100
17.6
29.5
0.6
4 months
12-20 years
16.1
3.7
17.9
2.9
21-30 years
45.7
7.1
34.3
15.7
31-44 years
38.2
2.3
27.5
10.5
Total
100
13.1
29.1
0.4
5 months
12-20 years
16.7
4.7
17.9
3.0
21-30 years
54.7
8.1
34.3
18.7
31-44 years
28.6
1.9
27.5
7.9
Total
100
14.6
29.6
0.5
6 months
12-20 years
15.0
3.6
17.9
2.7
21-30 years
53.8
8.4
34.3
18.4
31-44 years
31.2
2.5
27.5
8.6
Total
100
14.5
29.7
0.5
7 months
12-20 years
16.2
4.2
17.9
2.9
21-30 years
51.3
8.1
34.3
17.6
31-44 years
32.5
2.2
27.5
8.9
Total
100
14.5
29.4
0.5
8 months
12-20 years
14.4
2.5
17.9
2.6
21-30 years
51.5
7.6
34.3
17.7
31-44 years
34.1
3.6
27.5
9.4
Total
100
13.7
29.6
0.5
9 months
12-20 years
14.9
2.9
17.9
2.7
21-30 years
56.0
6.1
34.3
19.2
31-44 years
29.1
2.3
27.5
8.0
Total
100
11.3
29.9
0.4
6
Appendix Table 4B Illustrating Indirect Age Standardization Using Non-Pregnant Women as the
Reference Population (95%C.I)
Participants (%)
Observed
Age specific prevalence
Expected
in each age
prevalence (%) (%) among non-pregnant
prevalence (%)
group
females
1 month
12-20 years
(6.3, 11.0)
(17.6, 18.2)
(1.8, 6.2)
(15.2, 22.5)
21-30 years
(40.9, 53.6)
(8.4, 14.5)
(33.7, 34.8)
(12.3, 21.1)
31-44 years
(27.7, 41.4)
(3.9, 12.8)
(26.9, 28.1)
(6.5, 13.5)
Total
(21.6, 32.2)
(23.8, 34.6)
2 months
12-20 years
(14.0, 19.1)
(4.3, 7.1)
(17.6, 18.2)
(1.7, 5.00)
21-30 years
(46.4, 56.2)
(10.7, 16.2)
(33.7, 34.8)
(14.3, 21.4)
31-44 years
(27.3, 37.9)
(3.4, 9.3)
(26.9, 28.1)
(6.6, 11.9)
Total
(20.7, 28.7)
(25.4, 33.8)
3 months
12-20 years
(14.7, 20.2)
(4.0, 6.7)
(17.6, 18.2)
(1.9, 5.3)
21-30 years
(48.7, 58.9)
(7.9, 13.9)
(33.7, 34.8)
(15.2, 22.3)
31-44 years
(23.9, 34.5)
(1.0, 3.9)
(26.9, 28.1)
(5.8, 10.8)
Total
(14.4, 21.4)
(25.5, 33.8)
4 months
12-20 years
(13.7, 18.9)
(2.7, 4.9)
(17.6, 18.2)
(1.8, 4.7)
21-30 years
(40.7, 50.7)
(5.6, 9.1)
(33.7, 34.8)
(12.8, 19.1)
31-44 years
(32.9, 43.9)
(0.9, 5.9)
(26.9, 28.1)
(8.2, 13.4)
Total
(10.5, 16.3)
(25.3, 33.1)
5 months
12-20 years
(14.2 , 19.4)
(3.6, 6.1)
(17.6, 18.2)
(1.9, 4.7)
21-30 years
(49.9 , 59.5)
(6.1, 10.8)
(33.7, 34.8)
(15.8, 22.2)
31-44 years
(23.8, 34.0)
(0.9, 3.7)
(26.9, 28.1)
(5.9, 10.4)
Total
(12.0, 17.8)
(26.0, 33.5)
6 months
12-20 years
(12.6, 17.7)
(2.7, 4.8)
(17.6, 18.2)
(1.5, 4.7)
21-30 years
(48.6, 58.8)
(6.1, 11.5)
(33.7, 34.8)
(15.1, 22.4)
31-44 years
(26.4, 36.6)
(1.2, 5.3)
(26.9, 28.1)
(6.3, 11.6)
Total
(11.5, 18.2)
(25.6, 34.2)
7 month
12-20 years
(13.8, 19.0)
(3.1, 5.5)
(17.6, 18.2)
(1.8, 4.6)
21-30 years
(46.1, 56.4)
(6.3, 10.5)
(33.7, 34.8)
(14.8, 20.8)
31-44 years
(27.4, 38.1)
(1.1, 4.5)
(26.9, 28.1)
(6.9, 11.5)
Total
(11.9, 17.5)
(25.9, 33.2)
8 month
12-20 years
(12.2, 16.9)
(1.8, 3.5)
(17.6, 18.2)
(1.5, 4.3)
21-30 years
(46.4, 56.5)
(5.9, 9.7)
(33.7, 34.8)
(14.6, 21.1)
31-44 years
(29.0, 39.6)
(2.0, 6.5)
(26.9, 28.1)
(7.2, 12.2)
Total
(11.0, 16.9)
(25.9, 33.7)
9 month
12-20 years
(12.0, 18.3)
(1.8, 4.5)
(17.6, 18.2)
(1.5, 4.8)
21-30 years
(49.3, 62.4)
(4.2, 8.7)
(33.7, 34.8)
(15.6, 23.5)
31-44 years
(22.9, 36.2)
(1.0, 5.2)
(26.9, 28.1)
(5.7, 11.2)
Total
(8.5, 14.9)
(25.5, 34.7)
7
Age
standardized
ratio
(0.7, 1.1)
(0.7, 1.0)
(0.5, 0.7)
(0.3, 0.6)
(0.4, 0.6)
(0.4, 0.6)
(0.4, 0.6)
(0.4, 0.6)
(0.3, 0.5)
References
Breslow, N.E., Day, N.E., 1975. Indirect standardization and multiplicative models for rates, with
reference to the age adjustment of cancer incidence and relative frequency data. J Chronic Dis 28, 289303.
Shiffman, S., Waters, A.J., Hickcox, M., 2004. The Nicotine Dependence Syndrome Scale: A
multidimensional measure of nicotine dependence. Nicotine & Tobacco Research 6, 327-348.
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