Introduction to systematic literature review
Nicholas Ngwili, ILRI
Online Training on Systematic Literature Review, ILRI Nairobi, 5-6 May 2020

Learning outcomes at the end of the
training
 Describe what is SLR and their rationale
 Differentiate SLR and traditional reviews
 Formulate the research question and write a SLR
protocol- we will discuss a few examples
 Carry out all the stages of a SLR – 6 stages

What is SLR
A review prepared using a systematic approach to
minimizing biases and random errors which is
documented in a material and methods section in
an a priori protocol. This is what makes a review
systematic

SLRs
 Require comprehensive search of all evidence
 Systematic reviews are observational studies – therefore also
prone to bias
 Should apply the same level of rigour to reviewing research
evidence as is used producing that research evidence in the
first place.

Def’ continued…
 A systematic review may, or may not, include a meta-analysis:
a statistical analysis of the results, which generally aim to
produce a single estimate of an intervention effect
 Represented in a forest plot
 The examination of variability or heterogeneity in study
results is also a critical outcome

History
 In 1975 under the term 'meta analysis'. The phrase was
coined by Gene Glass who conducted syntheses in the areas
of psychotherapy (Smith, Glass and Miller 1980) and class size
(Glass and Smith 1979).
 Archie Cochrane in 1972 urged health practitioners to practice
evidence-based medicine

History
 In 1987, the year before Cochrane died, he referred
systematic review of randomised controlled trials (RCT's) a
real milestone in the history of randomised trials and in the
evaluation of care, and suggested that other specialties
should copy the methods used
 The Cochrane Collaboration in 1993- international network of
researchers, academics, practitioners and users
 The Campbell collaboration adapted Cochrane methodology
to bring the same quality of systematic evidence to issues of
broader public policy.

Why SLR?
 Researchers cannot read all relevant literature!
 Lack of time, resources and skills-find, appraise and interpret
 Often lots of studies sometimes with conflicting findings
 Systematic reviews summarise the evidence
 For relevant questions about important uncertainties in a
particular topic
- Systematic reviews are very powerful tools but are poorly
understood

Traditional reviews vs SLR

Traditional Literatures vs SLR
Traditional reviews Systematic literature review
 Are descriptive,
 Involve a non- systematic search
of literature
 Are selective – one chooses to
read what is available, is of
interest
 Can sometimes be confusing
where similar studies provide
different results and conclusions.
 It is prone to bias.
 Involve using a clear, well defined
methodology to summarize past
research, with a focus to reduce
bias.
 May include a meta- analysis
where data from different
studies is pooled together an a
summary provided
 Rich in data to inform further
research or methodology.

Characteristics of systematic reviews
o A clearly stated set of objectives with pre-defined eligibility
criteria for studies;
o An explicit, reproducible methodology;
o A systematic search that attempts to identify all studies that
meet the eligibility criteria;
o An assessment of the validity of the findings of the included
studies, for example through the assessment of risk of bias; and
o A systematic presentation, and synthesis, of the characteristics
and findings of the included studies

Stages in SLR
Define your research question and inclusion criteria
Carry out comprehensive, systematic searches
Select eligible studies
Extract data
Assess risk of bias in included studies
Synthesise the evidence

The protocol- defines the process in detail
 Have protocol written down and possibly reviewed
 Define question and search strategies
 Define Inclusion/exclusion criteria
 Quality control
 Extract data: primary outcomes, populations and interventions
 Protocols can be registered;
https://www.crd.york.ac.uk/prospero/

Types of SLR
o Comparative Effectiveness Research -what works best
o Diagnostic test accuracy
o Prognosis
o EPOC and Health systems - Effective Practice and Organisation of Care
o Qualitative research
o Cost effectiveness and health economics
o Genomics
o Social science and the Campbell Collaboration

Comparative Effectiveness Research
• Randomised controlled trials
• Non-randomised and pseudo-randomised
• Observational studies - no allocation but with a comparator or
control group
• Large outcome studies or real world data - big data
• Case series - sequential or selected

Summary; source(https://croatia.cochrane.org/news/how-
make-systematic-literature-review-basics-methodology-and-practical-steps )

Reading materials
○ http://handbook.cochrane.org/
– Cochrane handbook of systematic reviews of interventions Eds
Higgins, Green

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