Table.

Distribution of baseline characteristics among entire eligible baseline sample and the subset with both baseline and follow-up data, overall and for knee symptoms and four OA outcomes^*,^†

	Overall		Outcome subpopulation
			Symptoms		Radiographic		Symptomatic		Severe radiographic		Severe symptomatic‡
	Baseline Only (n=1,400)	Analytic (n=1,518)	Baseline Only (n =765)	Analytic (n = 887)	Baseline Only (n = 974)	Analytic (n = 1,246)	Baseline Only (n = 1,190)	Analytic (n = 1,342)	Baseline Only (n = 1,306)	Analytic (n = 1,419)	Baseline Only (n = 1,374)	Analytic (n = 1,473)
	%	%	%	%	%	%	%	%	%	%	%	%
Socio-demographic characteristics
Age (years)
45–54	31	37	36	41	37	41	35	40	32	39	31	37
55–64	23	31	22	32	25	31	23	31	24	30	23	31
65–74	28	25	28	21	25	23	28	23	28	24	29	24
≥75	17	8	14	7	13	5	15	6	16	7	17	8
Sex
Men	47	41	51	44	49	42	48	42	47	41	47	41
Women	53	49	49	56	51	58	52	58	53	59	53	59
Race
Black	22	14	23	12	21	13	22	14	21	14	22	14
White	78	86	77	88	79	87	78	86	79	86	78	86
Marital status
Never married	3	3	3	3	4	3	4	3	4	3	4	3
Married	62	70	69	73	65	72	64	72	63	71	62	71
Separated/Divorced	12	8	10	7	12	9	12	8	12	8	12	8
Widowed	23	18	19	16	19	16	20	17	21	18	22	18
Annual household income
$0 – <$15,000	42	27	33	22	38	24	39	25	40	27	41	27
15,000 – <$35,000	24	30	26	31	25	31	25	31	25	31	24	30
$35,000+	13	22	19	27	15	24	14	23	13	23	13	23
Don't know	9	8	9	7	9	8	9	8	10	8	9	8
Refused	12	12	13	13	14	13	13	13	12	12	12	12
Highest education
Less than high school	27	14	22	9	24	13	25	13	26	14	27	14
Some/completed high school	48	54	47	53	49	54	49	54	50	54	48	54
Greater than high school	24	32	31	38	26	34	26	33	24	32	25	32
Knee OA risk factors
Self-reported BMI (kg/m2) at age 18
Underweight/Normal(<25)	88	91	88	93	88	92	88	92	89	91	88	92
Overweight/Obese (≥25)	12	9	12	7	12	8	12	8	11	9	12	8
Clinically measured baseline BMI (kg/m2)
Underweight/Normal(<25)	37	33	41	39	40	35	39	35	38	33	37	33
Overweight (25-<30)	39	43	39	43	40	43	39	43	40	43	39	44
Obese (≥ 30)	24	24	20	18	20	22	22	22	22	23	24	23
Obese Class I (30-<35)	17	18	16	14	15	17	16	17	16	17	16	17
Obese Class ≥ II (≥35)	7	7	4	4	6	5	6	5	6	6	7	6
History of knee injury
No	84	84	93	92	86	87	86	87	85	85	85	85
Yes	16	16	7	8	14	13	14	13	15	15	15	15
Knee symptoms (pain, aching and/or stiffness)
None	56	60	10	10	62	66	66	68	58	63	58	61
Yes	44	40	0	0	38	34	34	32	42	37	42	39
Severity of pain
None	57	61	10	10	62	66	67	68	59	63	58	61
Mild	11	16	0	0	9	15	8	14	11	15	12	16
Moderate	21	19	0	0	18	14	16	14	19	17	22	19
Severe	11	5	0	0	11	4	9	4	12	5	8	4
KL grade
0	46	51	52	59	64	61	54	57	49	54	47	53
1	26	32	26	32	36	39	30	37	27	34	27	33
2	22	12	18	7			13	5	24	12	20	10
3	4	3	3	1			2	1			5	3
4	2	1	1	0			0	0			2	1

^*Distributions (percentages) differ from those presented in Table 2 because they were derived using baseline sampling weights which were based on 1990 Population in six townships in Johnston County. First follow-up weights (based on 2000 Population in six townships in Johnston County) were applied when estimating distributions and IRs for the analytic sample (i.e., those with both baseline and first follow-up data) to make estimates representative of the population in six townships in Johnston County.

^†Eligible respondents in overall population are those who did not have pre-existing knee symptoms and KL grade ≥ 2 at baseline; eligible respondents in each subpopulation are those who did not have the pre-existing outcome at interest at baseline. Baseline only are those respondents who were eligible at baseline but did not have follow-up data; analytic population are those with both baseline and first follow-up data.

^‡Presence of symptoms (pain, aching, or stiffness) and severe pain

BMI, body mass index; K-L, Kellgren-Lawrence; OA, osteoarthritis