Table 7.

 Source of evidence from three large meta-analyses

Drug effects	Meta-analysis of cohort studies of blood pressure and risk of CHD and stroke (2002)25	Meta-analysis of trials of drugs by class and dose and blood pressure reduction (2003)32	Meta-analysis of “event” trials of drugs by class and reduction in CHD and stroke (present analysis)	Comment on evidence from event trials (present analysis)
Effect of drug on blood pressure according to:
Class of drug	Uninformative	Informative	Uninformative	Estimates diluted because 24% of participants stopped taking tablets
Dose of drug	Uninformative	Informative	Uninformative	Different participants took different doses; low dose not tested
No of drugs	Uninformative	Informative	Uninformative	Statistical power too low
Effect of blood pressure reduction on disease according to:
Pretreatment blood pressure	Informative	Uninformative	Informative	Significant reduction in disease events even at lowest blood pressure
Class of drug	Uninformative	Uninformative	Informative	Extensive
Age	Informative	Uninformative	Uninformative	One narrow age range (60-69 years)

CHD=coronary heart disease.