Table 1. Univariable and multivariable logistic regression analysis of predictors for non-response in the iMPaCT study by comparing participants (n = 1,063) and non-respondents (n = 12,595) aged 18–24 years visiting an STI clinic in November 2016 to June 2017.

	Participants		Non-respondents
	N	%	N	%	OR (95% CI)	aOR (95%CI)
Age
18–20 years	165	16	3057	24	1	1
21–22 years	342	32	4567	36	0.72 (0.59–0.87)	0.79 (0.65–0.96)
23–24 years	556	52	4971	40	0.48 (0.40–0.58)	0.54 (0.45–0.65)
Gender
Female	860	81	9018	72	1	1
Male	203	19	3577	28	1.68 (1.44–1.97)	1.73 (1.47–2.05)
Education level
Low/medium	120	11	3563	28	1	1
High	941	89	8692	69	0.31 (0.26–0.38)	0.40 (0.32–0.48)
Migration background
Ethnic Dutch	857	81	8955	71	1	1
Non-Dutch	206	19	3638	29	1.69 (1.45–1.98)	1.27 (1.08–1.49)
Symptoms
No	897	84	9649	77	1	1
Yes	166	16	2946	23	1.65 (1.39–1.96)	1.35 (1.14–1. 62)
GO/CT/SYPH past year
No	320	30	3092	24	1	-
Yes	129	12	1603	13	1.29 (1.04–1.60)	-
Not tested	614	58	7900	63	1.33 (1.15–1.53)	-
Partner notification
No	942	89	10684	85	1	1
Yes	121	11	1910	15	1.39 (1.15–1.70)	1.23 (1.01–1.51)
Number of partners in past six months
0–2 partners	374	35	6005	48	1	1
3–4 partners	396	37	3956	31	0.62 (0.54–0.72)	0.66 (0.57–0.77)
≥ 5 partners	293	28	2634	21	0.56 (0.48–0.66)	0.55 (0.47–0.65)
Condom use at last sexual contact
No	828	78	10072	80	1	1
Yes	228	22	2386	19	0.86 (0.74–1.00)	0.83 (0.71–0.98)

Footnote: Categories do not all add up to 100%, as missing values are not shown. Statistical associations are shown in in italic when the p-value is equal to or smaller than 0.1, and in bold when the p-value is equal to or smaller than 0.05.

Abbreviations: CT = Chlamydia; OR = crude odds ratio, aOR = adjusted odds ratio; CI = Confidence Interval; IC = Informed Consent; STI = Sexually Transmitted Infection; SYPH = Syphilis.