When Things Are Not as They Appear: Assessing the Adequacy of Cluster Randomization When Outcome Events Are Rare at Baseline

Table 5

Rate of sexual and other risk behaviors by intervention condition after adjusting for GLAT score¹.

	Total			Boys					Girls
	WW	FOYC	OR	(95% CL)	WW	FOYC	OR	(95% CI)	WW	FOYC	OR	(95% CI)
Suspended from school
Baseline	1.44	2.13	1.49	(0.50, 4.00)	1.24	2.84	2.28	(0.55, 9.36)	1.56	1.43	0.84	(0.18, 3.94)
6 months	0.92	1.48	1.63	(0.45, 5.88)	1.01	1.88	1.93	(0.34, 10.93)	0.84	1.04	1.15	(0.15, 8.67)
12 months	4.39	4.07	0.93	(0.44, 1.94)	5.73	5.90	1.03	(0.42, 2.52)	3.11	1.94	0.55	(0.13, 2.33)
18 months	8.95	6.49	0.69	(0.39, 1.24)	10.29	6.91	0.64	(0.29, 1.41)	7.88	5.99	0.73	(0.31, 1.72)
24 months	10.50	6.96	0.64	(0.36, 1.13)	11.15	6.84	0.59	(0.26, 1.33)	9.94	7.10	0.69	(0.31, 1.56)
36 months	16.88	12.81	0.72	(0.44, 1.17)	19.63	16.10	0.79	(0.41, 1.51)	14.80	9.42	0.59	(0.28, 1.25)
Drank alcohol
Baseline	23.79	19.82	1.25	(0.57, 1.08)	29.17	20.99*	0.64	(0.42, 0.99)	19.17	18.54	0.96	(0.60, 1.53)
6 months	18.11	19.12	1.85	(0.75, 1.56)	21.53	24.28	1.20	(0.73, 1.96)	14.87	13.77	0.91	(0.52, 1.59)
12 months	14.27	19.80*	2.69	(1.04, 2.22)	20.43	22.74	1.16	(0.71, 1.90)	8.69	16.40*	2.10	(1.13, 3.89)
18 months	22.36	22.61	1.86	(0.71, 1.44)	26.25	24.55	0.90	(0.55, 1.46)	18.92	20.37	1.11	(0.65, 1.87)
24 months	18.19	24.07*	1.91	(1.02, 2.10)	20.61	27.61	1.52	(0.93, 2.50)	15.99	20.35	1.36	(0.80, 2.31)
36 months	26.46	34.05*	1.34	(1.06, 2.02)	25.97	31.65	1.35	(0.83, 2.18)	26.70	36.86*	1.63	(1.05, 2.54)
Carried a knife as a weapon
Baseline	2.71	2.96	1.04	(0.39, 2.73)	4.97	5.55	1.14	(0.37, 3.51)	0.41	0.44	0.68	(0.01, 66.69)
6 months	2.60	4.26	2.00	(0.54, 7.14)	5.17	8.67	2.07	(0.46, 9.28)	0.00	0.00	NE
12 months	2.91	4.67	1.61	(0.64, 4.02)	5.41	7.55	1.36	(0.50, 3.67)	0.45	1.65	8.46	(0.32, 221.62)
18 months	5.40	7.01	1.32	(0.65, 2.65)	10.09	13.37	1.40	(0.69, 2.86)	0.62	0.39	NE
24 months	4.87	7.95	1.77	(0.92, 3.44)	8.92	13.42	1.63	(0.80, 3.30)	0.76	2.35	2.83	(0.38, 21.15)
36 months	12.08	13.06	1.06	(0.63, 1.76)	15.94	23.61	1.65	(0.76, 3.57)	7.46	2.74	0.41	(0.13, 1.26)
Carried a gun as a weapon
Baseline	0.77	0.75	0.76	NE	0.81	1.41	0.03	NE	0.68	0.08	NE
6 months	0.55	0.37	0.56	(0.05, 5.56)	0.56	0.84	1.46	(0.10, 20.83)	0.49	−0.10	NE
12 months	0.64	0.56	0.91	(0.08, 6.25)	1.31	1.11	0.69	(0.08, 6.10)	0.00	0.00	NE
18 months	−0.02	2.06	NE		0.28	2.25	NE		0.03	1.51	NE
24 months	0.92	0.61	0.58	(0.09, 3.85)	1.89	1.23	0.59	(0.09, 3.85)	0.00	0.00	NE
36 months	1.47	4.54*	3.80	(1.17, 12.31)	1.90	7.60*	4.41	(1.17, 16.68)	0.78	1.36	1.04	(0.04, 24.59)
Involved in a physical fight
Baseline	36.92	32.34	0.99	(0.58, 1.12)	44.46	36.91	0.73	(0.49, 1.10)	29.64	27.74	0.90	(0.58, 1.39)
6 months	27.74	26.45	0.91	(0.23, 3.54)	35.27	36.82	1.06	(0.34, 3.32)	20.12	15.89	0.81	(0.44, 1.26)
12 months	24.15	23.66	1.00	(0.63, 1.49)	30.01	34.75	1.27	(0.73, 2.21)	17.97	12.14	0.62	(0.34, 1.13)
18 months	33.43	31.14	0.91	(0.65, 1.28)	43.19	41.29	0.92	(0.58, 1.44)	23.85	20.83	0.87	(0.51, 1.48)
24 months	22.10	29.33*	1.49	(1.05, 2.13)	29.75	37.62	1.44	(0.90, 2.30)	14.44	20.99	1.58	(0.91, 2.73)
36 months	27.85	24.65	0.84	(0.58, 1.21)	33.13	34.65	1.07	(0.66, 1.73)	21.98	14.66	0.59	(0.33, 1.07)
Smoked cigarettes
Baseline	1.76	1.51	0.85	(0.28, 2.61)	2.83	1.57	0.52	(0.13, 2.14)	0.76	1.50	1.04	(0.07, 16.66)
6 months	2.72	2.62	0.92	(0.34, 2.34)	3.91	4.97	1.07	(0.39, 2.96)	1.12	0.58	NE
12 months	2.52	1.57	0.61	(0.21, 1.83)	3.94	2.40	0.57	(0.16, 1.97)	1.13	0.80	0.78	(0.09, 6.80)
18 months	1.64	3.65	1.91	(0.33, 11.21)	3.73	3.78	1.04	(0.30, 3.58)	0.84	2.51	3.26	(0.30, 35.80)
24 months	2.60	3.52	1.38	(0.56, 3.42)	3.35	4.85	1.30	(0.38, 4.47)	1.67	2.35	1.37	(0.32, 5.91)
36 months	1.65	3.00	1.86	(0.60, 5.75)	1.13	3.40	2.76	(0.47, 16.28)	2.12	2.43	1.22	(0.17, 8.87)
Used marijuana
Baseline	0.28	1.10	NE		0.44	1.77	NE		0.06	0.42	NE
6 months	0.47	1.13	3.04	(0.20, 45.63)	0.71	2.08	2.81	(0.26, 30.89)	3.13	0.10	NE
12 months	1.63	1.52	0.76	(0.17, 3.43)	3.12	2.70	0.77	(0.20, 3.00)	0.35	0.45	NE
18 months	1.95	2.47	1.24	(0.42, 3.68)	3.71	3.97	1.07	(0.34, 3.35)	0.20	1.24	NE
24 months	2.10	2.54	2.69	(0.52, 13.93)	3.62	6.89	1.89	(0.57, 6.28)	0.71	1.89	2.85	(0.21, 39.15)
36 months	2.78	5.43	1.83	(0.80, 4.18)	5.34	7.65	1.44	(0.58, 3.60)	0.58	2.88	5.76	(0.60, 55.65)
Used cocaine
Baseline	0.27	0.94	NE		−0.07	0.95	NE		−0.07	0.60	NE
6 months	0.32	0.97	3.60	(0.36, 35.82)	0.50	1.83	3.60	(0.36, 35.94)	0.00	0.00	NE
12 months	0.33	0.96	3.08	(0.14, 65.86)	0.73	0.25	NE		0.04	1.72	NE
18 months	1.00	0.23	0.23	(0.02, 2.55)	1.55	0.49	0.28	(0.02, 4.66)	4.39	0.00	NE
24 months	0.45	0.30	0.64	(0.05, 7.85)	0.30	0.70	1.44	(0.08, 26.20)	0.54	−0.12	NE
36 months	0.43	1.30	3.74	(0.37, 37.86)	0.74	2.07	3.08	(0.29, 32.56)	0.09	0.48	NE
Sold drugs
Baseline	0.60	1.45	2.36	(0.55, 10.18)	0.73	2.44	3.09	(0.56, 17.09)	0.43	42.00	0.74	(0.02, 23.60)
6 months	1.30	1.04	0.70	(0.10, 5.01)	2.71	2.00	0.70	(0.17, 2.89)	0.00	0.00	NE
12 months	0.50	1.22	2.57	(0.14, 47.32)	0.98	2.36	2.55	(0.14, 46.72)	0.00	0.00	NE
18 months	1.80	1.55	0.77	(0.21, 2.85)	3.57	2.65	0.67	(0.17, 2.61)	0.09	0.48	NE
24 months	1.38	3.28	2.52	(0.75, 8.48)	2.22	5.30	2.82	(0.72, 11.14)	0.58	1.02	1.50	(0.03, 70.25)
36 months	2.69	3.49	1.12	(0.45, 2.82)	4.05	6.07	1.04	(0.34, 3.18)	0.89	1.23	1.30	(0.16, 10.33)
Sexual initiation
Baseline	4.67	4.82	2.17	NE	6.38	8.39	2.85	NE	2.99	1.01	NE
6 months	9.46	9.90	1.07	(0.36, 3.15)	16.38	15.75	0.95	(0.11, 8.11)	2.85	4.07	2.64	(0.44, 15.84)
12 months	14.43	17.81	1.51	(0.45, 5.10)	23.33	27.85	1.44	(0.49, 4.23)	5.49	8.09	1.97	(0.74, 5.24)
18 months	18.03	22.45	1.45	(0.81, 2.59)	29.93	36.48	1.20	(0.62, 2.32)	6.11	8.70	1.81	NE
24 months	27.66	29.88	1.16	(0.79, 1.69)	43.01	43.34	1.05	(0.67, 1.63)	12.32	17.09	1.81	(0.96, 3.42)
36 months	35.10	43.08	1.39	(0.97, 1.86)	52.72	59.44	1.19	(0.79, 1.81)	18.02	26.55	1.64	(0.93, 2.89)
Condom use
Baseline	25.00	32.14	1.41	(0.08, 25.5)	37.10	30.64	0.76	(0.03, 19.37)	NE
6 months	15.21	24.81	1.85	(0.60, 5.70)	19.55	28.78	1.67	(0.52, 5.33)	NE
12 months	17.82	31.50	2.18	(0.92, 5.13)	20.68	35.23	2.13	(0.85, 5.35)	8.05	14.41	1.90	(0.12, 30.09)
18 months	18.80	24.34	1.39	(0.64, 3.06)	18.24	27.35	1.70	(0.71, 4.04)	20.08	7.60	0.27	(0.02, 3.94)
24 months	18.94	28.17	1.69	(0.89, 3.21)	19.67	26.50	1.48	(0.70, 3.15)	16.11	34.42	2.69	(0.73, 9.99)
36 months	32.00	44.50*	1.71	(1.05, 2.80)	33.26	52.86**	2.26	(1.26, 4.05)	29.78	22.07	0.65	(0.23, 1.83)

* 𝑃<0.05, **𝑃<0.01; NE: nonestimable.
¹Passing rates of the 2005 English Grade Level Achievement Test (GLAT) (scores of C or better) by school.