Table 1.

Studies quality assessment based on Downs and Black checklist

Row	Articles	Reporting	External validity	Internal validity-bias	Internal validity-confounding (selection bias)	Total
1	Sah et al. [ 26 ]	8	2	6	4	20
2	Ren Hao [ 27 ]	9	2	6	4	21
3	Schrapf et al. [ 28 ]	9	2	6	4	21
4	Lee et al. [ 29 ]	9	2	6	4	21
5	Liu et al. [ 30 ]	8	2	7	4	21
6	Tou et al. [ 31 ]	9	1	7	4	21
7	Buric et al. [ 32 ]	7	1	7	4	19
8	Prakash et al. [ 17 ]	7	1	7	4	19
9	Acuna and David [ 33 ]	9	2	6	4	21
10	Tumer et al. [ 34 ]	8	2	6	4	20
11	Lu et al. [ 35 ]	8	2	5	4	19
12	Phinyomark et al. [ 36 ]	9	2	6	4	21
13	Pobar et al. [ 37 ]	7	1	6	4	19
14	Novatchkov et al. [ 8 ]	9	2	6	4	21
15	Zhao et al. [ 38 ]	8	2	6	4	20
16	Fischer et al. [ 13 ]	9	2	6	4	21
17	Eskofier et al. [ 7 ]	9	2	6	4	21
18	Eskofier et al. [ 12 ]	8	2	6	4	20
19	Acikkar et al. [ 11 ]	9	2	6	4	21
20	Rozumalsk et al. [ 39 ]	7	1	7	4	19
21	Kim and Lee [ 40 ]	7	2	6	4	19
22	Silva et al. [ 41 ]	9	2	6	4	21
23	Xu et al. [ 42 ]	8	2	6	4	20
24	Pretorius et al. [ 43 ]	9	1	7	4	21
25	Juang ang Jih-Gau [ 44 ]	8	2	6	4	20
26	Lapham et al. [ 1 ]	8	2	6	4	20