systematicr e v i e w s

Adam DubrowskiNUR 1022, Lecture 5

Systematic Review

We will address the following 2 issues:

• How is a systematic review different than a narrative review of the literature?

• Advantages of the systematic review?

Systematic Review

• A systematic review is a literature review focused on a single question which tries to

– identify

– appraise

– select

– synthesize

all high quality research evidence relevant to that question.

Systematic Review

• Systematic reviews are regarded as the highest level of medical evidence by evidence-based medicine professionals.

• An understanding of systematic reviews and how to implement them in practice is becoming mandatory for all professionals involved in the delivery of health care.

Systematic Review

• There are mechanisms to overcome bias in the review which involves following a rigorous methodology.

1. Formulate a Research Question

1.1 Specify the Population, Intervention or Exposure, Methodology, Outcome (close to PICO)

1.2 Specify inclusion and exclusion criteria (of literature)

1.3 Determine restrictions: Time frame, Unpublished data, Language

The Process of Conducting a Systematic Review

1. Conduct Literature Search

2.1 Decide on information sources:

• bibliographical databases

• key journals

• articles, funding agencies, pharmaceutical company registries etc. (document!)

2.2 Identify Titles and Abstracts

The Process of Conducting a Systematic Review

1. Apply Inclusion and Exclusion Criteria

• Determine the minimum methodological standards that studies must meet

3.1 Apply inclusion and exclusion criteria to titles and abstracts

3.2 Obtain full study reports for eligible titles and abstracts

3.3 Apply inclusion and exclusion criteria to full study reports

3.4 Select final eligible studies

Document!

The Process of Conducting a Systematic Review

1. Abstract Data4.1 Assess methodological quality of studies (validity

assessment)

4.2 Abstract data from each study about participants, exposure or intervention, experimental design

4.3 Abstract results

The Process of Conducting a Systematic Review

1. Conduct analysis

5.1 Explore heterogeneity

5.2 Determine methods for summarizing results

5.3 Combine results if appropriate

(i.e. meta-analysis)

The Process of Conducting a Systematic Review

combining results

Meta-Analysis: statistical technique for quantitatively combining the results of multiple studies that measure the same outcomes into a single pooled summary estimate.

Combining Results

Combining Results

Study results are weighted by their sample size, which yields a weighted average.

There is usually a statistical test of heterogeneity among study weighted means = is the between study variance greater than expected by chance?

Confidence Intervals: range between two valueswithin which it is probably that the true value liesfor the whole population of patients from which thestudy patients were selected.

Differences Among Studies

How Precise Were the Results?

• Wide confidence intervals can results from a lack of precision resulting from inclusion of a small number of studies.

How Precise Were the Results?

• Wide confidence intervals can results from a lack of precision resulting from inclusion of a small number of studies.

• The selective publication of manuscripts based on the magnitude, direction or statistical significance of the study results.

Publication Bias

Authors decide that reporting a negative study is worthless and uninteresting.

Report completion

Interim analysis shows that a study is likely to be negative, and the study is dropped.

Study completion

No registries were kept of approved trials –this has recently changed.

Institution/ Ethics Review Board approval

Proposal selectively cites positive studies.Trial design, organization, and funding

Small studies, which are more likely to be negative less likely to be published.

Preliminary and pilot studies

Actions Contributing to BiasPhases of research publication

Success of Publication Bias

Applying the Results to Patient Care

Consider whether:

• The population sample covered by the review could be different from your population in ways that would produce different results?

• Your local setting differs from that of the review?

• You can provide the same intervention in your setting?

1. How Can I apply the Results to Patient Care

Consider outcomes from the point of view of the:

• Individual

• Policy makers and professionals

• Family/careers

• Wider community

Systematic reviews frequently do not report the adverse effects of treatment.

2. Were all Patient-Important Outcomes Considered?

Consider:• Whether any benefit reported outweighs any harm and/or

cost. If this information is not reported can it be filled in from elsewhere?

3. Are the Benefits worth the Cost and Potential Risks?