98 PART 2 Examining Tools and Processes

interventions, randomized clinical trials containing a control group (called

randomized controlled trials, or RCTs) are usually required, but for other exposures,

either case-control or cohort study designs are required. With respect to

­medications, RCTs are required as part of regulatory approval for distribution (see

Chapter  5), so expect to see meta-analyses arising from results from clinical

trials. In a systematic review, the studies included are compared and summarized

in a table, but their numerical estimates coming from their results are not com-

bined. The meta-analysis is the same as a systematic review except the numerical

estimates coming from the results reported are combined statistically to produce

an overall estimate based on the studies included. Systematic reviews and meta-

analyses are described in more detail in Chapter 20.

If you are looking for the highest quality of evidence right now about a current

treatment or exposure and outcome, read the most recent systematic reviews

and meta-analyses on the topic. If there aren’t any, it may mean that the treat-

ment, exposure, or outcome is new, and that there are not a lot of high quality

observational or experimental studies published on the topic yet.