| Study | Reason for exclusion |
|---|---|
| Carayon 1985a | Unclear randomisation procedure |
| Carayon 1985b | Unclear randomisation procedure |
| Carayon 1993 | Unclear randomisation procedure |
| Dandapat 1991 | Unclear randomisation procedure |
| Droogenbroeck 1977 | No randomisation procedure |
| Oommen 1979 | No randomisation procedure |
| Rao 1989 | No randomisation procedure |
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