Figure 8.6.a: Example of a ‘Risk of bias’ table for a single study (fictional)

Entry

Judgement

Support for judgement

Random sequence generation (selection bias)

Low risk.

Quote: “patients were randomly allocated.”

Comment: Probably done, since earlier reports from the same investigators clearly describe use of random sequences (Cartwright 1980).

Allocation concealment (selection bias)

High risk.

Quote: “...using a table of random numbers.”

Comment: Probably not done.

Blinding of participants and personnel (performance bias)

Low risk.

Quote: “double blind, double dummy”; “High and low dose tablets or capsules were indistinguishable in all aspects of their outward appearance. For each drug an identically matched placebo was available (the success of blinding was evaluated by examining the drugs before distribution).”

Comment: Probably done.

Blinding of outcome assessment (detection bias) (patient-reported outcomes)

Low risk.

Quote: “double blind”.

Comment: Probably done.

Blinding of outcome assessment (detection bias) (Mortality)

Low risk.

Obtained from medical records; review authors do not believe this will introduce bias.

Incomplete outcome data addressed (attrition bias) (Short-term outcomes  (2-6 weeks))

High risk.

4 weeks: 17/110 missing from intervention group (9 due to 'lack of efficacy'); 7/113 missing from control group (2 due to 'lack of efficacy').

Incomplete outcome data addressed (attrition bias) (Longer-term outcomes  (>6 weeks))

High risk.

12 weeks: 31/110 missing from intervention group; 18/113 missing from control group. Reasons differ across groups.

Selective reporting (reporting bias)

High risk.

Three rating scales for cognition listed in Methods, but only one (with statistically significant results) is reported.