Study Design 101

Systematic Review


A document often written by a panel that provides a comprehensive review of all relevant studies on a particular clinical or health-related topic/question. The systematic review is created after reviewing and combining all the information from both published and unpublished studies (focusing on clinical trials of similar treatments) and then summarizing the findings.



Design pitfalls to look out for

Studies included in systematic reviews may be of varying study designs, but should collectively be studying the same outcome.

Is each study included in the review studying the same variables?

Some reviews may group and analyze studies by variables such as age and gender; factors that were not allocated to participants.

Do the analyses in the systematic review fit the variables being studied in the original studies?

Fictitious Example

Does the regular wearing of ultraviolet-blocking sunscreen prevent melanoma? An exhaustive literature search was conducted, resulting in 54 studies on sunscreen and melanoma. Each study was then evaluated to determine whether the study focused specifically on ultraviolet-blocking sunscreen and melanoma prevention; 30 of the 54 studies were retained. The thirty studies were reviewed and showed a strong positive relationship between daily wearing of sunscreen and a reduced diagnosis of melanoma.

Real-life Example

Pittler MH, Guo R, Ernst E. Hawthorn extract for treating chronic heart failure. Cochrane Database of Systematic Reviews 2008, Issue 1. Art. No.: CD005312.

This systematic review analyzed fourteen studies (randomized, double-blinded, and placebo controlled) that used hawthorn leaf and flower extract monopreparations to determine whether there is any benefit or harm in using hawthorn extract to treat chronic heart failure when compared to placebo. The authors determined that hawthorn extract provides “significant benefit in symptom control and physiologic outcomes” when used as an adjuvant treatment for chronic heart failure.

Related Terms

Now test yourself!

1. Systematic Reviews are similar to Meta-Analyses, except they do not include a statistical analysis quantitatively combining all the studies.

a) True
b) False

2. The panels writing Systematic Reviews may include which of the following publication types in their review?

a) Published studies
b) Unpublished studies
c) Cohort studies
d) Randomized Controlled Trials
e) All of the above

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