exposure of having high prediagnosis alcohol intake. What is the overall answer? Does high alcohol

intake cause liver cancer or not? You could also imagine that multiple cohort studies could be

conducted examining association between the exposure of high alcohol intake and developing the

outcome of HTN. How would the results of these cohort studies be taken together to answer the

question of whether high alcohol intake actually causes HTN?

The answer to this question are systematic reviews and meta-analyses. In a systematic review,

researchers set up inclusion and exclusion criteria for reports of studies. Included in those criteria are

requirements for a certain study design. For 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

combined. 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 treatment, exposure, or outcome is new, and that there are

not a lot of high quality observational or experimental studies published on the topic yet.