Table 2. Methodological quality of trials based on the Jadad scale (n = 14).
| No. | Source (project name) | Randomization | Description of randomization methods | Double-blind | Using identical placebo | Follow-up reporting | Total score |
|---|---|---|---|---|---|---|---|
| 1 | 1977 Byar and Blackard | 1 | 0 | 0 | 0 | 1 | 2 |
| 2 | 1994 Lamm et al. | 1 | 1 | 1 | 1 | 1 | 5 |
| 3 | 1994 ATBC | 1 | 1 | 1 | 1 | 1 | 5 |
| 4 | 1996 CARET | 1 | 0 | 1 | 1 | 1 | 4 |
| 5 | 1999 WHS | 1 | 1 | 1 | 1 | 1 | 5 |
| 6 | 2000 Decensi et al. | 1 | 1 | 1 | 0 | 1 | 4 |
| 7 | 2000 PHS | 1 | 0 | 1 | 1 | 1 | 4 |
| 8 | 2002 NPC | 1 | 1 | 1 | 1 | 1 | 5 |
| 9 | 2003 IHNCSG | 1 | 1 | 0 | 0 | 1 | 3 |
| 10 | 2005 Bairati et al. | 1 | 1 | 1 | 1 | 1 | 5 |
| 11 | 2008 Sabichi et al. | 1 | 1 | 1 | 1 | 1 | 5 |
| 12 | 2010 Nepple et al. | 1 | 1 | 1 | 1 | 1 | 5 |
| 13 | 2012 SELECT | 1 | 1 | 1 | 1 | 1 | 5 |
| 14 | 2012 Mazdak and Zia | 1 | 0 | 0 | 0 | 1 | 2 |
ATBC = the Alpha-tocopherol Beta-carotene Cancer Prevention Study, CARET = the Beta-Carotene and Retinol Efficacy Trial, WHS = the Women's Health Study, PHS = the Physicians' Health Study, NPC = Nutritional Prevention of Cancer, IHNCSG = the Italian Head and Neck Chemoprevention Study Group, SELECT = Selenium and Vitamin E Cancer Prevention Trials.