CHAPTER 7 Having Designs on Study Design 97

Advancing to the clinical trial stage

Higher up the pyramid of evidence shown in Figure 7-2 are experiments. Not all

experiments are at such a high level of evidence — only high-quality clinical tri-

als. These are experiments, not observational studies. This is where the researcher

assigns the participants to engage in a particular behavior or intervention during

the study. There are different types of clinical trials as described in Chapter 5;

however, the highest-quality trials use both double-blinding and randomization.

Double-blinding is where both the researcher and the participant do not know

whether the participant was assigned to an active intervention (one being stud-

ied), or a control intervention. Randomization is where participants are randomly

assigned to groups (so there is no bias in selecting participants for each group).

It is possible to use a 2x2 table to analyze the results of a high-quality clinical trial

as long as the rows are replaced with the intervention groups. You can report the

same measure of relative risk as for a cohort study; however, the difference is that

the high-quality clinical trial would be seen as having much less bias than the

cohort study — and stronger causal evidence.

Reaching the top: Systematic reviews

and meta-analyses

Imagine a scenario where a new drug for HTN was developed, and several clinical

trials were conducted to see whether this drug was better than the most popular

current drug used for HTN. How would we be able to know whether, on balance,

the new drug was actually better when we have so many different clinical trials on

the same drug with different results?

We could ask a similar question about observational studies as well. Imagine that

multiple case-control studies were conducted to determine whether having liver

cancer was associated with the 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 develop-

ing 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 sys-

tematic review, researchers set up inclusion and exclusion criteria for reports of

studies. Included in those criteria are requirements for a certain study design. For