Table 2.

Costs and number of participants recruited by online recruitment methods.

Online advertising campaigns		Characteristics		Participants N			Average costs per participant €
				Tracked	Tracked per 30 days	Self-reported	Tracked	Tracked and self-reported
Netdoktor.dk
	Snart-Gravid.dk	One campaigna, 31 months		2273	73	0	3.93a	N/Ab
	SnartForældre.dk	One campaigna, 24 months		639	27	59	2.99a	2.74
Minmave.dk		Five campaigns, 1 month each		689	138	7	14.93	14.78
			October 1, 2012	212		N/A	9.70	N/A
			January 20, 2013	158		N/A	13.02	N/A
			March 1, 2013	142		N/A	14.49	N/A
			May 14, 2013	88		N/A	23.37	N/A
			August 31, 2013	89		N/A	23.11	N/A
Sundhedsguiden.dk		One campaign, 8 months		11	1	1	115.12	105.53
Baby.dk		One campaign, 3 months		19	6	2	45.40	41.08
AU.dk		Postings on AUc intranet and AU Facebook page		4	N/A	0	0.00	N/A
Facebook		Seven nationwide advertisements, 8-10 days each		230	121	50	3.44	2.83
All online methods				3866	53	119	6.22	6.04

^aNegotiated, fixed price per recruited participant.

^bN/A: not available.

^cAU: Aarhus University.