Table 2.
Quality assessment of the included studies.
| Study | Random sequence generation |
Allocation concealment |
Blinding of participants personnel and outcome assessors | Incomplete outcome data |
Selective outcome reporting |
Other sources of bias |
|---|---|---|---|---|---|---|
| Keech et al. 1994 | L | L | H | L | L | L |
| Salonen et al. 1995 | L | L | L | L | L | L |
| Herd et al. 1997 | U | U | L | L | L | U |
| Patrick et al. 2002 | U | U | L | L | L | U |
| Downs et al. 1998 | U | U | L | L | L | L |
| Shepherd et al. 1995 | U | U | L | L | L | L |
| Pedersen et al. 1994 | L | L | L | L | L | L |
| Tonkin 1998 | U | U | L | L | L | L |
| Sacks et al. 1996 | L | U | L | L | L | L |
| Shepherd et al. 2002 | L | L | L | L | L | L |
| Armitage et al. 2009 | L | L | L | L | L | L |
| Bays et al. 2004 | U | U | H | L | L | U |
| Baigent et al. 2005 | U | U | L | L | L | U |
| Furberg et al. 1994 | U | U | L | L | L | L |
| Newman et al. 2008 | U | U | L | L | L | H |
| Bradford et al. 1991 | U | U | L | L | L | U |
L: low risk of bias; H: high risk of bias; U: unclear risk of bias.