Table 2. The methodological quality of included studies based on the Cochrane handbook.
| Study | A | B | C | D | E | F | Total |
|---|---|---|---|---|---|---|---|
| Toyokur 198517 | + | − | + | − | ? | + | 3 |
| Olanow 199418 | ? | − | + | − | + | − | 2 |
| Steiger 199619 | ? | + | + | − | ? | − | 3 |
| Hutton 199620 | ? | − | + | − | + | + | 3 |
| Rascol 199621 | − | − | + | − | ? | ? | 1 |
| Lieberman 199722 | ? | − | + | − | + | + | 3 |
| Guttman 199723 | ? | − | + | + | ? | + | 3 |
| Wermuth 199824 | + | − | + | − | + | ? | 3 |
| Lieberman 199825 | + | − | + | − | + | + | 4 |
| Pinter 199926 | + | − | + | + | ? | + | 4 |
| Stocchi 200227 | ? | − | − | + | + | + | 3 |
| Nyholm 200528 | + | + | + | − | + | + | 5 |
| Moller 200529 | + | − | + | − | ? | + | 3 |
| Peter 200730 | + | + | + | − | + | + | 5 |
| Poewe 200731 | ? | + | + | − | + | + | 4 |
| R. Pahwa, 200732 | + | ? | + | − | + | + | 4 |
| Hauser 200933 | + | − | + | − | + | + | 4 |
| Pablo 201134 | + | − | − | ? | + | − | 2 |
| Schapira 201135 | − | ? | + | ? | + | + | 3 |
| Olanow 201436 | + | + | + | + | + | + | 6 |
A: Sequence generation; B: Allocation concealment; C: Blinding of participants, personnel and outcome assessors; D: Incomplete outcome data; E: Selective outcome reporting; F: Other sources of bias; +: Yes; −: No; ?: Unclear.