Table 3.

Quality score criteria

Ref. no.	Year	External validity							Internal validity						Informativity
		a	b	c	d	e	f	Sum	g	h	i	j	k	Sum	l	m	n	o	p	q	r	Sum	Disagreement
[19]	2011	+	+	−	−	−	+	3	−	+	+	+	+	4	+	+	+	+	+	+	−	6	c, i, r
[10]	2011	+	+	−	−	−	+	3	−	+	+	+	+	4	+	+	+	+	+	+	+	7	i, o, r
[20]	2013	+	+	+	+	+	+	6	−	+	+	+	+	4	+	+	+	+	+	+	+	7	d, h
[22]	2014	+	+	−	−	+	+	4	−	+	+	+	+	4	+	+	+	+	+	+	+	7	h
[23]	2012	+	+	+	+	+	+	6	−	+	+	+	+	4	+	+	+	+	−	+	+	6	c, e
[21]	2014	+	+	+	+	+	+	6	−	+	+	+	+	4	+	+	+	+	+	+	+	6	r
[24]	2010	+	−	−	−	−	+	2	−	+	−	−	+	2	+	+	+	−	−	+	−	4	j, o
Total		6	5	2	2	3	6		0	6	5	5	6		6	6	6	5	4	6	4
Mean								4.3						3.7								6.1

Items a–r refer to the quality score criteria listed in “Appendix 2”