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Systematic Reviews in the Health Sciences: Getting Started

Gain an understanding of systematic reviews, scoping reviews and other evidence synthesis methodologies from start to finish.
Last Updated: May 7, 2024 1:03 PM


Don't underestimate the amount of time required for a systematic review. Most teams are balancing multiple projects and responsibilities in addition to the systematic review. The following table can help you better understand a typical length of commitment necessary for a systematic review.

Timeline of a Systematic Review
Steps General Amount of Time Needed Per Step
Protocol Development 1-2 months
Searching the Literature 1-5 months
Assessment of the Literature (Two Stages) 1-5 months
Data Collection 1-7 months
Analysis 1-3 months
Preparation of Manuscript 1-10 months



Development of Inclusion and Exclusion Criteria

In a systematic review, the criteria for including and exclusing studies (eligibility criteria) must be explicitly stated and defined early in the process.

These clear, consistent rules can make the screening process more efficient and helps reduce bias. Each study must be compared against the same criteria, meet all inclusion criteria and not meet any exclusion criteria.

Be sure to have a conflict resolution process in place for when screeners disagree on inclusion or exclusion of a study. This might be through discussion or identifying a tie breaker vote from an additional screener.

Common inclusion and exclusion criteria include:

  • Date
  • Exposure of interest
  • Geographic location of the study
  • Language
  • Participants
  • Peer review
  • Reported outcomes
  • Setting
  • Study design
  • Types of publication

Research Question Development

PICO (Patient-Intervention-Comparison-Outcome) is a well-known and used framework for structuring clinical research questions. Note that especially in systematic searching, the O or Outcome is often not included in the search. Instead it may be part of the review of results.

PECO (Population-Exposure-Comparison-Outcome) is another variant sometimes used for public health and social science reviews.

PICO: Patient/Problem, Intervention; Comparison; Outcome

PEO (Population-Exposure-Outcome) is a variant framework commonly used in Public Health and related disciplines and is useful when investigating a prognosis or likelihood of developing a condition as a result of an exposure.

Population or patient: Who you are interested in studying? How would you describe the population of interest?

Exposure: What pre-existing condition does the population of interest/patient have or what has the population of interest/patient been exposed to?

Outcome: What is the outcome of interest? While in PICO the O is often not included in the search, in PEO, it almost always is.

PICO is sometime further adapted to exclude or include content. PIO, for example, focuses on the Patient/Problem/Patient, Intervention/Issue, and Outcome. PICOT(T) adds in two additional fields: 

Time: A limit may be placed to review content from a particular time frame either built into the search or applied during review of results

Type of Study: If you are only interested in certain study designs, you might limit to a certain type during the search or, more likely, apply this inclusion/exclusion criteria during the review of results

Spider SilhouetteSPIDER is a framework adapted from PICO. It is sometimes used for qualitative research.

S: Sample Size

PI: Phenomenon of Interest

D: Study Design

E: Evaluation

R: Research Type