Table 2. Evaluation of methodological quality using Bogardus method.

Study	1	2	3	4	5	6	7
Aydemir et al.21	no	yes	yes	yes	yes	no	yes
Härtel et al.9	no	yes	yes	yes	yes	no	yes
Abu-Maziad et al.22	no	yes	yes	yes	yes	no	no
Auriti et al.23	no	yes	yes	yes	yes	no	yes
Koroglu et al.24	no	yes	yes	yes	yes	no	yes
Spiegler et al.25	no	yes	yes	yes	yes	no	yes
Abdel-Hady et al.26	no	yes	yes	yes	yes	no	yes
Bertalan et al.27	no	yes	yes	yes	yes	no	no
Reiman et al.28	no	yes	yes	yes	yes	no	yes
Dzwonek et al.29	no	yes	yes	yes	yes	no	yes
van Der Zwet et al.30	no	yes	yes	no	no	no	yes
Schueller et al.31	no	yes	yes	yes	no	yes	yes
Derzbach et al.32	no	yes	yes	yes	yes	no	no
Härtel et al.33	no	yes	yes	yes	yes	no	yes
Baier et al.34	no	yes	yes	yes	yes	yes	yes
Göpel et al.35	no	yes	yes	yes	yes	no	yes
John Baier et al.36	no	yes	yes	yes	yes	no	no
Hedberg et al.37	no	yes	yes	yes	yes	no	no
Ahrens et al.38	no	yes	yes	yes	yes	no	yes
Bessler et al.39	no	yes	yes	yes	yes	no	yes
Harding et al.40	yes	yes	yes	yes	yes	yes	yes
Treszl et al.41	no	yes	yes	yes	yes	no	yes

1 = reproducibility; 2 = definition of cases; 3 = adequacy of cases; 4 = definition of control; 5 = adequacy of control; 6 = objectivity; 7 = quantification of results.