Included Study Study Design Allocation Concealment Blinding of Intervention Blinding of Outcome Complete Follow up Gross 1983 RCT Yes No Unclear Yes Tyson 1983 RCT Yes No Unclear Yes Cooper 1984 quasi-RCT Unclear No Unclear Yes Lucas 1990 A RCT Yes No Unclear Yes Lucas 1990 B RCT Yes No Unclear Yes Schanler 2005 RCT Yes No Unclear Yes Note: Lucas 1990A and Lucas 1990B were parallel studies in one trial. RCT: randomized controlled trial.

Table 2: Methodological quality of the included studies.