Table 1.

Sample characteristics among all participants and among all observations.

	Individual participants (n=3087)		Total observations (n=6775)
Sample characteristics	na	%b	n	%
Time-point
Wave 3 (June 2004–December 2004)	1135	36.77	1135	16.75
Wave 4 (October 2005–January 2006)	1164	37.71	1164	17.18
Wave 5 (October 2006–February 2007)	1138	36.86	1138	16.80
Wave 6 (September 2007–February 2008)	1130	36.61	1130	16.68
Wave 7 (October 2008–February 2009)	1242	40.23	1242	18.33
Wave 8 (July 2010–January 2011)	966	31.29	966	14.26
Total number of waves participated
2	959	31.07	959	14.15
3	844	27.34	1379	20.35
4	491	15.91	1257	18.55
5	311	10.07	1015	14.98
6	212	6.87	869	12.83
7	122	3.95	553	8.16
8	148	4.79	743	10.97
Sex
Female	1764	57.14	3973	58.64
Male	1323	42.86	2802	41.36
Baseline age group (years)
18–24	200	6.48	349	5.15
25–39	621	20.12	1229	18.14
40–54	1242	40.23	2854	42.13
55+	1024	33.17	2343	34.58
Race/ethnicity
Non-Hispanic white	2579	83.54	5760	85.02
Other	500	16.20	987	14.57
Unknown	8	0.26	28	0.41
Education
Low	1259	40.78	2680	39.56
Moderate	1244	40.30	2750	40.59
High	607	19.66	1331	19.65
Unknown	6	0.19	14	0.21
Income
Low	1182	38.29	2382	35.16
Moderate	1150	37.25	2312	34.13
High	832	26.95	1708	25.21
Unknown	217	7.03	373	5.51
HSI
0–1	861	27.89	1426	21.05
2–3	1752	56.75	3131	46.21
4–6	1172	37.97	2056	30.35
Unknown	27	0.87	162	2.39

^aNumber of individuals in each category of each variable. Sum of ns exceeds total number of participants inasmuch as individual participants are present in more than one category of a variable at different time-points.

^bPercentage is given out of total number of participants, some of whom contributed more than one observation. HSI = heaviness of smoking index.