eTable 2. Studies used for forward searching.

Study	Date	Number of studies citing the study
Studies included for analysis
Fernandes et al. (2018) (29)	18 June 2019	n = 5
Iosifidis et al. (2015) (30)	18 June 2019	n = 9
Kujala et al. (1994) (25)	18 June 2019	n = 162
Kujala et al. (1995) (31)	18 June 2019	n = 266
Roos et al. (1994) (1)	18 June 2019	n = 112
Sandmark & Vingard (1999) (27)	18 June 2019	n = 46
Thelin et al. (2006) (28)	18 June 2019	n = 56
Tveit et al. (2012) (32)	18 June 2019	n = 59
Vrezas et al. (2010) (26)	18 June 2019	n = 43
Primary studies relevant to topic*
Arliani et al. (2014) (16)	11 September 2019	n = 16
Arliani et al. (2016) (e14)	11 September 2019	n = 0
Behzadi et al. (2017) (e15)	11 September 2019	n = 2
Brouwer et al. (1981) (17)	11 September 2019	n = 4
Elleuch et al. (2008) (18)	11 September 2019	n = 32
Klünder et al. (1980) (19)	11 September 2019	n = 92
Lau et al. (2000) (20)	11 September 2019	n = 144
Lv et al. (2018) (21)	11 September 2019	n = 0
Matiotti et al. (2017) (e22)	11 September 2019	n = 1
Östenberg (2001) (22)	11 September 2019	n = 0
Paxinos et al. (2016) (23)	11 September 2019	n = 6
Söder et al. (2011) (e27)	11 September 2019	n = 15
Volpi et al. (2019) (24)	11 September 2019	n = 0

* Excluded on grounds of recruitment method and/or response rate