Table 1. Overview on measured variables and items.

Dimension	Variable	Reference	Reliability
Age, biological maturation	chronological age (years) relative age (month) age at peak height velocity (years)	Mirwald et al., 2002	rtt = .96
Anthropometry	height (cm) weight (kg)		rtt = .99 rtt = .99
Coach assessment	in-game performance (points)	Zuber and Conzelmann, 2014	W = .89
General motor performance	YoYo (m) counter-movement-jump (cm) 40 m-sprint (sec) agility test (sec)	Bangsbo et al., 2008 Casartelli et al., 2010 Zuber et al., 2016 Höner et al., 2015	rtt = .93 ICC = .96 rtt = .96 rtt = .83
Technical skills	dribbling (sec) passing (sec) juggling (points)	Höner et al., 2015 Zuber et al., 2016 Höner et al., 2015; Zuber et al., 2016	rtt = .56 rtt = .68 rtt = .79
Psychological characteristics	achievement motive (net-hope) achievement goal orientations (score) self-determination (index)	Wenhold et al., 2009 Elbe, 2004 Pelletier et al., 1995; Demetriou, 2012	α = .76/.73 α = .80/.72/.81 α = .86
Familial support	importance of football within family (score) parents’ priority of sport vs. school (score) financial investment (Swiss Francs / year) time investment (h / week)		rtt = .63 rtt = .52 rtt = .78 rtt = .59
Training history	practice and play up to 12 years of age (h)	Hopwood, 2015	.59 ≤ rtt ≤ .97