Table 2.
Quality assessment of randomised controlled trials of the effect of omega 3 fats on mortality, cardiovascular disease, and cancer
|
Study
|
Concealment of allocation
|
Masking
|
Dropouts for analysis of events (intervention, control)
|
|||
|---|---|---|---|---|---|---|
| Participants | Providers of care | Assessors of outcome | Summary risk of bias | |||
| Almallah 1998w1 | Done | Yes | Yes | Yes | ?/18, ?/18 | Low |
| Bairati 1992w2 | Done | Yes | Yes | Yes | 48/107, 38/98 | Low |
| Bellamy 1992*w3 | Unclear | Unclear | Unclear | Unclear | 3/60, 7/60 | Medium or high |
| Belluzzi 1996w4 | Done | Yes | Yes | Yes | 5/39, 2/39 | Low |
| Bemelmans 2002w5 | Done | Yes | Yes | Yes | ?/51, ?/52 | Low |
| Bonnema 1995w6 | Done | Yes | Yes | Yes | 0/14, 1/14 | Low |
| Borchgrevink 1966w7 | Done | Yes | Yes | Yes | ?/100, ?/100 | Low |
| Brox 2001w8 | Unclear | No | Yes | Yes | Seal oil 8/40, cod liver oil 2/40, 1/40 | Medium or high |
| Burr (DART) 1989w9 | Unclear | No | No | Yes | 0/1015, 0/1018 for mortality | Medium or high |
| Burr 2003w10 | Unclear | No | No | Yes | 0/1571, 0/1543 for mortality | Medium or high |
| Connor 1993w11 | Done | Yes | Yes | Yes | ?/8, ?/8 | Low |
| Dehmer 1998w12 | Not done | No | No | No | 3/46, 5/44 | Medium or high |
| Dry 1991w13 | Done | Yes | Yes | Yes | 0/6, 0/6 | Low |
| Eritsland 1996w14 | Done | No | No | Yes | 15/317, 14/293 | Medium or high |
| Franzen 1993w15 | Unclear | Yes | Unclear | Yes | 0/15, 0/15 | Medium or high |
| Geusens 1994*w16 | Unclear | Yes | Yes | Yes | Low dose 9/30, high dose 11/30, 10/30 | Medium or high |
| GISSI-P 1999*w17 | Done | No | Unclear | Yes | ?/5665, ?/5658 | Medium or high |
| Greenfield 1993w18 | Done | Yes | Yes | Yes | 3/16, 1/8 | Low |
| Hawthorne 1992w19 | Done | Unclear | Yes | Yes | 5/49, 6/47 | Medium or high |
| Johansen 1999*w20 | Unclear | Yes | Yes | Yes | 54/250, 58/250 | Medium or high |
| Katan 1997w21 | Done | No | Unclear | Yes | Low dose ?/15, med dose ?/15, high dose ?/14, ?/14 | Medium or high |
| Kaul 1992w22 | Unclear | No | No | Yes | ?/58, ?/49 | Medium or high |
| Lau 1993w23 | Done | Yes | Yes | Yes | 9/32, 16/32 | Low |
| Lau 1995w24 | Done | Yes | Yes | Yes | 0/25, 0/20 | Low |
| Leaf 1994w25 | Done | Yes | Yes | Yes | 69/275, 69/276 | Low |
| Loeschke 1996w26 | Done | Yes | Yes | Yes | 0/31, 0/33 | Low |
| Lorenz-Meyer 1996w27 | Done | Yes | Yes | Yes | ?/70, ?/65 | Low |
| Malaguarnera 1999*w28 | Unclear | No | Unclear | Unclear | ?/26, ?/26 | Medium or high |
| Maresta 2002w29 | Done | Yes | Yes | Yes | 44/169, 38/170 | Low |
| Mate-Jimenez 1991w30 | Done | No | Yes | Yes | 4/19, 6/19 | Medium or high |
| Milner 1989w31 | Done | No | Unclear | Yes | 0/100, 0/100 | Medium or high |
| Natvig 1968*w32 | Done | Yes | Yes | Yes | 2/6716, 2/6690 | Low |
| Nilsen 2001w33 | Done | Yes | Yes | Yes | ?/150, ?/150 | Low |
| Nye 1990*w34 | Unclear | Yes | Yes | Yes | 0/36, 0/37 | Medium or high |
| Reis 1991w35 | Done | Yes | Yes | Yes | 22/146, 10/72 | Low |
| Rossing 1996w36 | Done | Yes | Yes | Yes | 0/18, 0/18 | Low |
| Sacks (HARP) 1995*w37 | Unclear | Yes | Yes | Yes | 10/41, 11/39 | Medium or high |
| Sacks (TOHP 1) 1994*w38 | Done | Yes | Yes | Yes | 1/175, 1/175 | Low |
| Sarkkinen 1998w39 | Unclear | No | No | Yes | 0/41, 0/37 | Medium or high |
| Selvais 1995w40 | Done | Yes | Yes | Yes | 4/12, 2/12 | Low |
| Shimizu 1995w41 | Not done | No | No | Yes | ?/29, ?/16 | Medium or high |
| Singh 1997†w42 | Done | No | Yes | Yes | Fish oil 4/122, mustard oil 8/120, 6/118 | Medium or high |
| Sirtori 1998w43 | Done | Yes | Yes | Yes | 28/470, 39/465 | Low |
| Skoldstam 1992w44 | Done | No | No | No | 1/23, 2/23 | Medium or high |
| Terano 1999w45 | Done | No | No | Yes | 0/10, 0/10 | Medium or high |
| Thien 1993w46 | Done | Yes | Yes | Yes | 6/21, 6/16 | Low |
| Veale 1994w47 | Done | Yes | Yes | Yes | 4/19, 0/19 | Low |
| von Schacky 1999w48 | Done | Yes | Yes | Yes | ?/112, ?/111 | Low |
Allocation concealment was coded as done, unclear, or not done; blinding of participants, providers, and outcome assessors was coded as yes (where there was a clear and realistic attempt to blind—success of blinding was rarely checked in the studies), unclear, or no (in consultation with authors of trials where possible).
A trial was considered to be at low risk of bias if allocation concealment was “done” and blinding of participants, providers, and outcome assessors was coded “yes.” All other trials were considered at moderate or high risk of bias.
Did not respond to our request for further information on the quality of their studies or provide additional data on trial outcomes.
The BMJ has concerns about the validity of another paper written by this author.18