Table 2.

Results of the methodological quality assessment (+=positive; -=negative)

Study	Methodological quality									Total score	Total %	Quality
	1	2	3	4	5	6	7	8	9
Christensen 2012 [24]	+	+	+	-	+	+	+	+	+	8/9	89	High
Coile 2000 [35]	+	+	+	-	-	-	+	+	+	6/9	67	High
de Preter 2013 [20]	+	+	+	+	-	+	+	+	+	8/9	89	High
Gesthuizen 2011 [22]	+	+	+	+	-	+	+	+	+	8/9	89	High
Gortz 2012 [25]	+	+	+	+	+	+	+	+	+	9/9	100	High
Herquelot 2011 [26]	+	+	+	-	-	-	+	+	+	6/9	67	High
Heyma 2004 [27]	+	+	+	-	-	+	-	+	+	6/9	67	High
Kerkhofs 1999 [28]	+	+	+	-	-	+	+	+	+	7/9	78	High
Marton 2010 [36]	+	+	+	-	-	+	+	+	+	7/9	78	High
Montizaan 2013 [33]	+	+	+	-	-	+	+	+	+	7/9	78	High
Olesen 2012 [29]	+	+	+	-	-	+	-	+	+	6/9	67	High
Ӧrestig 2013 [37]	+	+	+	-	+	+	+	+	+	8/9	89	High
Roberts 2009 [30]	+	+	+	+	-	+	+	+	+	8/9	89	High
Robroek 2013 [31]	+	+	+	-	-	+	+	+	+	7/9	78	High
Rubb 2009 [23]	+	+	+	-	-	+	+	+	+	8/9	89	High
Schils 2008 [21]	+	+	+	+	-	+	+	+	+	7/9	78	High
Schuring 2013 [32]	+	+	+	-	+	+	+	+	+	8/9	89	High
Song 2008 [12]	+	+	+	-	+	-	-	+	+	6/9	67	High
van Solinge 2010 [7]	+	+	+	+	-	+	+	+	+	8/9	89	High
van Solinge 2011 [34]	+	+	+	-	-	+	-	+	+	6/9	67	High