Benefits of extensive recruitment effort persist during follow-ups and are consistent across age group and survey method. The TRAILS study

Table 6 Substance use of participants who responded to the custom research company hired at the fourth TRAILS measurement wave (T4-easy-to-recruit), participants who responded after extra recruitment effort of the TRAILS research team (T4-hard-to-recruit), participants who did not respond at the fourth wave but did participate in the third wave (non-responder T4) and of participants who had dropped out from TRAILS prior to the fourth wave (drop-out since T2 or T3)

	T4-easy-to-recruit (ref.)	T4-hard-to-recruit			Non-responder T4			Drop-out since T2 or T3
	n(%)	n(%)	OR	95% CI	n(%)	OR	95% CI	n(%)	OR	95% CI
Lifetime substance use
T2 Tobacco lifetime prevalence	533 (33.7)	107 (44.0)	1.55*	1.18-2.03	62 (50.8)	2.03*	1.40-2.94	56 (39.7)	1.30	0.91-1.84
T2 Alcohol lifetime prevalence	1,162 (73.9)	194 (79.8)	1.40*	1.00-1.95	92 (76.7)	1.16	0.75-1.80	103 (72.5)	0.93	0.64-1.37
T2 Cannabis lifetime prevalence	100 (6.3)	28 (11.6)	1.94*	1.25-3.02	11 (9.3)	1.52	0.79-2.92	14 (10.1)	1.65	0.92-2.98
T3 Tobacco lifetime prevalence	819 (57.1)	89 (70.6)	1.81*	1.21-2.69	69 (70.4)	1.79*	1.14-2.79	-
T3 Alcohol lifetime prevalence	1,345 (93.9)	125 (98.4)	4.04	0.98-16.62	92 (93.9)	0.99	0.42-2.33	-
T3 Cannabis lifetime prevalence	439 (30.7)	45 (35.4)	1.24	0.85-1.81	35 (36.5)	1.29	0.84-1.99	-
T4 Tobacco lifetime prevalence	1,153 (72.7)	100 (81.3)	1.64*	1.03-2.61	-			-
T4 Alcohol lifetime prevalence	1,146 (98.2)	121 (99.2)	2.27	0.31-16.81	-			-
T4 Cannabis lifetime prevalence	841 (53.1)	66 (55.0)	1.08	0.75-1.57	-			-

*p < .05; Odds ratios (OR) and 95% confidence intervals (CI) from logistic regression analyses; n varies between 2,074 and 2,087 (T2), 1,651 and 1,658 (T3), and 1,697 and 1,710 (T4).

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