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

Table 3

Intervention effect of youth participating in WW+GFI and FOYC+CImPACT overall and by gender on nonsexual risk behaviors controlling for age and baseline differences.

	Total				Boys				Girls
	WW	FOYC	OR^¥	(95% CL)	WW	FOYC	OR	(95% CL)	WW	FOYC	OR	(95% CL)
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)
Carried a knife as a weapon
Baseline	2.50	3.13	1.25	(0.57, 2.75)	4.90	5.63	1.16	(0.50, 2.66)	0.43	0.41	0.87	(0.04, 19.30)
6 months	2.59	4.39	1.85	(0.83, 4.12)	5.33	8.70	1.77	(0.78, 4.01)	0.00	0.00	NE
12 months	2.26	5.40*	2.69	(1.20, 6.03)	4.12	8.77	2.31	(0.98, 5.49)	0.50	1.59	6.63	(0.36, 121.59)
18 months	4.59	7.95*	1.86	(1.01, 3.44)	9.22	14.20	1.63	(0.87, 3.18)	0.47	0.57	0.57	(0.02, 15.91)
24 months	4.59	8.08*	1.91	(1.04, 3.51)	8.83	13.50	1.66	(0.85, 3.22)	0.94	2.14	2.14	(0.37, 12.42)
36 months	10.75	13.78	1.34	(0.85, 2.10)	15.81	23.56	1.68	(0.97, 2.90)	6.65	3.56	0.52	(0.20, 1.37)
Carried a gun as a weapon
Baseline	0.81	0.69	0.85	(0.19, 3.86)	0.87	1.31	1.52	(0.25, 9.30)	0.74	0.00	NE
6 months	0.45	0.47	1.01	(0.14, 7.42)	0.48	0.92	1.92	(0.17, 21.70)	0.42	−0.02	NE
12 months	0.47	0.75	1.58	(0.26, 9.64)	1.01	1.39	1.39	(0.23, 8.54)	0.00	0.00	NE
18 months	0.00	1.93	NE		0.00	2.51	NE		0.00	1.22	NE
24 months	0.73	0.77	1.06	(0.21, 5.32)	1.61	1.48	0.92	(0.19, 4.66)	0.00	0.00	NE
36 months	1.08	4.81**	4.79	(1.58, 14.47)	1.87	7.64*	4.51	(1.26, 16.16)	0.42	1.82	4.17	(0.43, 40.81)
Involved in a physical fight
Baseline	36.41	32.75	0.85	(0.65, 1.12)	44.49	36.88	0.73	(0.50, 1.06)	29.51	28.25	0.94	(0.63, 1.41)
6 months	28.87	24.83	0.81	(0.59, 1.10)	39.31	34.09	0.79	(0.53, 1.19)	20.14	15.78	0.74	(0.45, 1.21)
12 months	23.41	24.75	1.08	(0.78, 1.49)	30.70	34.55	1.20	(0.79, 1.82)	16.95	13.44	0.76	(0.44, 1.32)
18 months	31.89	32.87	1.05	(0.77, 1.42)	42.10	42.51	1.02	(0.67, 1.54)	22.97	21.56	0.91	(0.56, 1.50)
24 months	21.21	29.92**	1.60	(1.16, 2.22)	28.55	38.72*	1.60	(1.04, 2.46)	15.03	20.27	1.44	(0.86, 2.43)
36 months	26.23	25.75	0.98	(0.70, 1.34)	33.23	34.55	1.06	(0.68, 1.65)	20.79	16.27	0.74	(0.43, 1.25)
Smoked cigarettes
Baseline	1.68	1.55	0.89	(0.31, 2.53)	2.82	1.58	0.51	(0.13, 1.95)	0.74	1.48	2.00	(0.33, 12.17)
6 months	2.36	2.95	1.25	(0.54, 2.89)	4.14	4.79	1.17	(0.46, 2.98)	0.77	1.06	1.18	(0.16, 8.76)
12 months	2.35	1.79	0.76	(0.28, 2.03)	3.98	2.38	0.59	(0.19, 1.85)	0.94	1.04	1.09	(0.14, 8.41)
18 months	1.96	3.54	1.83	(0.74, 4.51)	3.79	3.92	1.03	(0.36, 2.96)	0.44	3.00	6.82	(0.78, 59.34)
24 months	2.48	3.61	1.48	(0.64, 3.45)	3.28	4.90	1.52	(0.53, 4.41)	1.79	2.20	1.24	(0.30, 5.16)
36 months	1.62	3.06	1.94	(0.68, 5.58)	1.27	3.26	2.43	(0.45, 13.17)	2.00	2.70	1.39	(0.34, 5.69)
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	16.4*	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)
Used marijuana
Baseline	0.22	1.15	5.50	(0.63, 47.77)	0.45	1.76	3.99	(0.44, 36.47)	0.01	0.48	NE
6 months	0.66	0.97	1.47	(0.32, 6.68)	0.92	1.88	2.05	(0.37, 11.41)	0.41	−0.01	NE
12 months	1.42	1.78	1.25	(0.41, 3.78)	2.53	3.25	1.29	(0.40, 4.18)	0.43	0.00	NE
18 months	1.73	2.73	1.58	(0.59, 4.23)	3.67	4.02	1.10	(0.39, 3.12)	0.01	1.21	NE
24 months	2.00	4.62*	2.37	(1.01, 5.56)	3.29	7.31	2.32	(0.87, 6.17)	0.90	1.64	1.82	(0.30, 11.23)
36 months	2.78	5.23	1.93	(0.90, 4.17)	5.77	7.23	1.27	(0.54, 3.00)	0.45	3.06	7.01	(0.80, 61.24)
Used cocaine
Baseline	−0.02	0.72	NE		0.00	0.88	NE		−0.02	0.52	NE
6 months	0.25	0.94	3.92	(0.42, 36.23)	0.53	1.81	3.63	(0.39, 33.54)	0.00	0.00	NE
12 months	0.26	0.99	3.90	(0.43, 35.81)	0.53	0.44	0.80	(0.05, 13.94)	0.02	1.66	NE
18 months	0.96	0.28	0.29	(0.03, 2.59)	1.57	0.50	0.32	(0.03, 3.15)	0.45	0.01	NE
24 months	0.49	0.25	0.50	(0.04, 5.73)	0.56	0.74	0.81	(0.05, 13.85)	0.44	0.01	NE
36 months	0.28	1.41	5.34	(0.61, 46.72)	0.64	2.17	3.52	(0.38, 32.83)	−0.02	0.62	NE
Sold drugs
Baseline	0.66	1.34	2.04	(0.50, 8.37)	0.95	2.14	2.31	(0.44, 12.32)	0.40	0.46	1.06	(0.06, 17.92)
6 months	1.15	1.16	0.93	(0.26, 3.36)	2.47	2.24	0.88	(0.24, 3.18)	0.00	0.00	0.00
12 months	0.48	1.28	2.66	(0.51, 13.96)	1.02	2.37	2.31	(0.45, 12.49)	0.00	0.00	0.00
18 months	1.44	1.97	1.37	(0.46, 4.13)	3.07	3.15	1.03	(0.32, 3.26)	0.00	0.61	NE
24 months	1.11	3.52*	3.39	(1.09, 10.54)	1.79	5.82	3.57	(0.98, 13.04)	0.51	1.02	1.99	(0.17, 23.17)
36 months	2.86	3.12	1.08	(0.46, 2.57)	5.37	4.88	0.88	(0.33, 2.33)	0.86	1.28	1.38	(0.19, 10.05)

^∗𝑃<0.05,^∗∗𝑃<0.01 NE: nonestimable; ^¥odds ratios.