The methodological quality of the identified studies was assessed using a scoring system developed by Jadad et al. (See Other Publications of Related Interest). A point was given for each of the following criteria if they were met:
1. The study was described as randomised and included the use of words such as 'random', 'randomly' and 'randomisation'.
2. The study was described as double-blind.
3. Withdrawals and drop-outs were described.
4. The method of randomisation was described and appropriate (e.g. random number tables or computer-generated).
5. The method of double-blinding was described as appropriate (e.g. identical placebo, active placebo, dummy).
In addition one point was deducted if:
6. The method of randomisation was described and inappropriate (e.g. alternate allocation or allocation by date of birth, hospital number).
7. If the method of double-blinding was described and inappropriate (comparison of tablet versus injection with no double dummy).
A maximum of 5 points could be achieved. In terms of methodological quality, papers were given a score of a maximum of 5 points. The assessment was carried out by two independent reviewers and any disagreements were resolved by discussion.