Table 4. Quality appraisal.

	The study sample represents the population of interest on key characteristics	Was there an adequate response rate?	Was the case definition specified and is it reproducible?
Boling (2010) [13]	✓	✓	✓
Clarsen (2010) [12]	✓	✓	✓
Coppack (2011) [79]	✓	✓	✓
Devan (2004) [26]	X	✓	✓
Dey (2016) [83]	✓	✓	✓
Fairbank (1984) [27]	✓	X	X
Finnoff (2011) [28]	✓	X	✓
Hall (2015) [29]	X	✓	✓
Herbst (2015) [30]	X	✓	X
Kaufman (1999) [80]	X	✓	✓
Milgrom (1991) [17]	X	✓	X
Molgaard (2011) [9]	✓	✓	✓
Myer (2010) [16]	X	✓	✓
Nejati (2010) [11]	X	Unknown	✓
Rathleff (2014) [84]	✓	✓	✓
Roush (2012) [5]	✓	✓	✓
Steinberg (2012) [31]	X	✓	X
Thijs (2011) [82]	X	✓	✓
Thijs (2007) [32]	✓	✓	✓
Weiss (1985) [24]	✓	✓	✓
Wills (2004) [81]	✓	✓	✓
Winslow (1995) [85]	X	Unknown	✓
Witvrouw (2000) [18]	Unknown	X	✓

✓, yes; X, no