Epidemiology can identify potential policy interventions, synthesize existing knowledge regarding their effectiveness, contribute relevant new research, and assess the potential of each approach. Clinical epidemiologists have become very good at synthesizing existing knowledge in their development of systematic reviews and meta-analysis, but the process is not so easy for the population-level interventions that are most often used in policy, since randomized studies are rarely possible; the current debate on application of meta-analysis to observational studies is very relevant to policy-oriented epidemiology.