Table 2 Methodological quality of studies.

Muldoon 2000 [28]

Lovastatin (20 mg)/placebo

Trained data collectors were blinded to subjects' treatment assignment. Method of randomization unclear.

All analyses were conducted on an intention-to-treat basis. 7% attrition rate. Difference in education levels of completers versus drop outs, but no other key characteristics. In several instances, test scores were transformed to ensure normality.

Wardle 1996 [23]

Simvastatin 20 mg or 40 mg daily/placebo

Follow-up data collection was blinded. Method of randomization unclear.

Intention to treat used. Medians and IQRs used. Study had good statistical power to detect a shift in the distribution of the total score of the profile of mood questionnaire.

Hyyppa 2003 [23]

Simvastatin 20 mg/day plus dietary intervention/placebo

All measurements and analyses were performed blinded to the treatment allocation of the participant. Method of randomization unclear.

Intention to treat not mentioned, however attrition rate was 0%. Where necessary, log or square root transformations were applied.

Harrison 1994 [24]

Sequential placebo, pravastatin 40 mg day/simvastatin 40 mg day, in separate 4-week treatment phases

Volunteers were blind to which medication they were receiving. Investigators were blind to drugs administered during the treatment phases but not the placebo washout phases. Method of randomization unclear.

Intention to treat not mentioned, however attrition rate was 0%

Gengo 1995 [25]

Placebo, lovastatin (40 mg), and pravastatin (40 mg) for 4 weeks

Method of randomization or concealment unclear

Intention to treat not mentioned, however attrition rate was 0%

Stewart 2000 [26]

Pravastatin sodium (40 mg/day) for 4 years

Process of randomization or concealment was unclear

Intention to treat used, with the exception of the relation between a change in cholesterol level and psychological outcome. Baseline response rate was 93%. Response rate at follow-up assessments: the response rate was 90% at 6 months, 90% at 1 year, 88% at 2 years, and 77% at 4 years.

Morales 2006 [27]

Simvastatin up to 20 mg/day or placebo for 15 weeks

Blinding: To maintain the double-blind, all medication was prepared in opaque, identical-appearing red-and-blue gelatin capsules, which were sealed in blister cards with each individual dose identified on the packaging by the day and the time it was to be taken. Process of randomization unclear.

Intention to treat analysis used. Mixed effects models used. Where data were not normally distributed, data were transformed/used as binary outcomes. Results were reported in terms of the change in positive affect per day. Given a high degree of colinearity between group assignment and final cholesterol status, these models did not control for treatment group in the analysis of the effect of cholesterol status on outcome. In all, 79% of subjects assigned to placebo and 80% receiving simvastatin completed the study.