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

Table 2

Sexual risk and protection intervention effect of youth participating in WW+GFI and FOYC+CImPACT overall and by gender controlling for age and baseline differences.

	Total				Boys				Girls
	WW	FOYC	OR^¥/ES	(95% CL)	WW	FOYC	OR/ ES	(95% CL)	WW	FOYC	OR/ES	(95% CL)
Sexual initiation %
Baseline	4.13	5.33	1.26	(0.67, 2.38)	5.90	8.78	1.54	(0.73, 3.29)	2.68	1.42	0.49	(0.12, 1.97)
6 months	9.30	10.08	1.18	(0.64, 2.19)	16.34	15.99	0.96	(0.48, 1.89)	2.85	4.07	2.51	(0.45, 13.90)
12 months	14.71	17.75	1.36	(0.88, 2.10)	24.51	26.73	1.16	(0.70, 1.94)	5.75	7.74	1.59	(0.61, 4.14)
18 months	17.64	23.28*	1.54	(1.04, 2.93)	30.39	36.33	1.37	(0.86, 2.19)	6.17	8.61	1.63	(0.66, 4.06)
24 months	25.69	31.50	1.39	(0.99, 1.94)	41.06	45.14	1.20	(0.78, 1.84)	12.30	16.91	1.55	(0.83, 2.89)
36 months	33.14	43.73**	1.62	(1.19, 2.21)	51.36	60.69	1.48	(0.96, 2.28)	18.43	26.00	1.63	(0.97, 2.73)
Sex intention %
Baseline	2.84	6.23*	2.28	(1.15, 4.52)	5.24	10.02	2.04	(0.96, 4.33)	0.80	1.97	2.45	(0.44, 13.79)
6 months	5.55	6.33	1.16	(0.64, 2.10)	10.52	9.92	0.93	(0.48, 1.82)	1.21	2.65	2.20	(0.52, 9.37)
12 months	5.13	10.30**	2.23	(1.25, 3.96)	9.26	16.75*	2.07	(1.09, 3.94)	1.31	2.89	2.16	(0.51, 9.23)
18 months	6.18	8.75	1.47	(0.82, 2.63)	10.61	14.10	1.42	(0.73, 2.77)	2.30	2.47	1.07	(0.28, 4.08)
24 months	6.08	9.08	1.59	(0.89, 2.81)	10.93	16.06	1.62	(0.85, 3.07)	1.84	1.67	0.90	(0.20, 4.13)
36 months	10.22	16.04*	1.73	(1.09, 2.73)	18.91	26.33	1.56	(0.92, 2.65)	2.94	5.40	1.85	(0.63, 5.46)
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)
Condom Intention %
Baseline	26.54	37.15**	1.64	(1.22, 2.20)	31.58	44.54*	1.74	(1.16, 2.63)	22.51	29.28	1.43	(0.92, 2.20)
6 months	40.89	44.81	1.18	(0.88, 1.59)	46.29	48.86	1.11	(0.73, 1.69)	36.07	40.97	1.24	(0.82, 1.90)
12 months	47.66	57.13*	1.49	(1.10, 2.01)	47.46	58.09*	1.58	(1.03, 2.42)	47.49	56.49	1.47	(0.96, 2.26)
18 months	39.70	60.28**	2.37	(1.74, 3.25)	43.74	57.85*	1.79	(1.15, 2.77)	36.03	63.48**	3.36	(2.12, 5.33)
24 months	53.56	69.41**	2.01	(1.47, 2.77)	52.33	64.14*	1.66	(1.06, 2.60)	54.23	75.23**	2.64	(1.66, 4.22)
36 months	68.51	77.94**	1.64	(1.15, 2.33)	65.35	76.44*	1.74	(1.05, 2.88)	70.73	79.66	1.64	(0.99, 2.73)
HIV knowledge
Baseline	0.70	0.71	0.06	(0.05, 0.08)	0.68	0.70	0.17	(0.16, 0.19)	0.72	0.73	0.09	(0.07, 0.10)
6 months	0.74	0.80**	0.41	(0.40, 0.42)	0.71	0.79**	0.78	(0.77, 0.79)	0.77	0.82**	0.48	(0.47, 0.50)
12 months	0.57	0.59	0.11	(0.09, 0.13)	0.59	0.58	0.08	(0.06, 0.10)	0.56	0.60*	0.32	(0.30, 0.33)
18 months	0.56	0.63**	0.38	(0.36, 0.40)	0.59	0.64*	0.38	(0.37, 0.40)	0.54	0.62**	0.62	(0.60, 0.64)
24 months	0.55	0.62**	0.40	0.38, 0.42)	0.57	0.63**	0.49	(0.47, 0.51)	0.52	0.62**	0.80	(0.79, 0.82)
36 months	0.57	0.66**	0.46	(0.44, 0.48)	0.58	0.69**	0.82	(0.80, 0.84)	0.56	0.63**	0.50	(0.48, 0.52)
Condom skills
Baseline	0.54	0.55	0.06	(0.04, 0.07)	0.57	0.56	0.08	(0.07, 0.10)	0.55	0.55	0.00	(−0.02, 0.02)
6 months	0.55	0.61**	0.34	(0.32, 0.35)	0.56	0.62**	0.48	(0.46, 0.50)	0.54	0.60**	0.47	(0.46, 0.49)
12 months	0.57	0.59	0.11	(0.09, 0.13)	0.59	0.58	0.08	(0.06, 0.10)	0.56	0.60*	0.32	(0.30, 0.33)
18 months	0.56	0.63**	0.38	(0.36, 0.40)	0.59	0.64*	0.38	(0.37, 0.40)	0.54	0.62**	0.62	(0.60, 0.64)
24 months	0.55	0.62**	0.40	0.38, 0.42)	0.57	0.63**	0.49	(0.47, 0.51)	0.52	0.62**	0.80	(0.79, 0.82)
36 months	0.57	0.66**	0.46	(0.44, 0.48)	0.58	0.69**	0.82	(0.80, 0.84)	0.56	0.63**	0.50	(0.48, 0.52)
Self-efficacy
Baseline	2.37	2.26	0.09	(−0.20, 0.01)	2.55	2.40	0.18	(0.08, 0.29)	2.22	2.10	0.14	(0.03, 0.25)
6 months	2.81	3.20**	0.39	(0.29, 0.48)	2.93	3.34**	0.58	(0.48, 0.67)	2.71	3.05**	0.47	(0.38, 0.56)
12 months	2.81	3.16**	0.31	(0.21, 0.48)	2.99	3.37**	0.48	(0.37, 0.59)	2.65	2.92*	0.35	(0.24, 0.45)
18 months	3.00	3.51**	0.47	(0.36, 0.58)	3.17	3.74**	0.74	(0.63, 0.85)	2.84	3.25**	0.54	(0.43, 0.64)
24 months	3.12	3.60**	0.46	(0.36, 0.56)	3.35	3.83**	0.66	(0.55, 0.76)	2.92	3.34**	0.57	(0.46, 0.67)
36 months	3.49	3.91**	0.42	(0.32, 0.52)	3.82	4.21**	0.57	(0.47, 0.67)	3.23	3.58**	0.49	(0.39, 0.59)
Resp. efficacy
Baseline	3.87	3.93	0.06	(−0.03, 0.15)	3.99	3.99	0.00	(−0.09, 0.09)	3.77	3.87	0.14	(0.05, 0.23)
6 months	3.98	4.24**	0.31	(0.23, 0.38)	4.05	4.30**	0.42	(0.34, 0.50)	3.91	4.18**	0.45	(0.37, 0.53)
12 months	4.00	4.26**	0.29	(0.20, 0.37)	4.06	4.32**	0.40	(0.32, 0.49)	3.94	4.20*	0.41	(0.32, 0.49)
18 months	4.08	4.39**	0.37	(0.28, 0.45)	4.27	4.37	0.17	(0.08, 0.25)	3.92	4.40**	0.81	(0.73, 0.89)
24 months	3.97	4.31**	0.41	(0.33, 0.49)	4.05	4.35**	0.51	(0.43, 0.59)	3.91	4.27**	0.61	(0.53, 0.69)
36 months	4.13	4.40**	0.33	(0.25, 0.41)	4.21	4.44**	0.41	(0.32, 0.49)	4.07	4.35**	0.48	(0.39, 0.56)

* 𝑃<0.05, **𝑃<0.01; NE: nonestimable; ^¥ for categorical outcomes odds ratios were reported and effect sizes for continuous outcomes.