Formulating a clear and focused research question is the first and most critical step in planning a systematic review. A systematic review is not an exploratory venture—it is a structured and methodical process designed to answer a specific, pre-defined research question using rigorous, reproducible methods. Without a well-formulated question to guide the review, the entire process risks becoming unfocused, biased, and ultimately uninformative.
If you are considering conducting a literature review but do not have a specific research question in mind, a narrative review, scoping review, or critical review may be more appropriate. These other types of reviews allow for a broader exploration of a topic without the constraints of a predefined research question.
However, if your goal is to conduct a systematic review, your first task is to frame a research question that clearly identifies the population, context, phenomenon of interest, or intervention being examined. To aid in this process, several established frameworks can be used to develop systematic review questions tailored to different types of evidence and objectives.
Common Frameworks for Formulating Systematic Review Questions
The format of your research question depends on the type of systematic review you plan to conduct—be it qualitative, quantitative, or mixed-methods. Below are the most widely used frameworks and the types of reviews they are best suited for:
1. PICO – For Reviews of Interventions
Best for: Quantitative reviews evaluating the effects of interventions.
P – Population or Patient
I – Intervention
C – Comparison
O – Outcome
Example: In adults with hypertension (P), does daily meditation (I) compared to no intervention (C) reduce blood pressure (O)?
Why PICO?
PICO is ideal for clinical and health-related research where the goal is to assess the effectiveness of specific interventions or treatments. It structures the question in a way that facilitates comparison and meta-analysis.
2. PEO – For Qualitative Evidence Syntheses
Best for: Qualitative reviews exploring experiences, perceptions, or lived realities.
P – Population
E – Exposure (or phenomenon of interest)
O – Outcome (or themes/perspectives)
Example: What are the experiences (O) of transgender women (P) in accessing PrEP (E) in the United States?
Why PEO?
PEO is tailored for questions that do not seek to compare interventions but rather understand subjective perspectives or social phenomena in specific contexts.
3. SPIDER – For Qualitative and Mixed-Methods Reviews
Best for: Qualitative and mixed-methods research where sampling and evaluation methods are critical.
S – Sample
PI – Phenomenon of Interest
D – Design
E – Evaluation
R – Research type
Example: Among frontline nurses (S), how is stress (PI) explored (D), measured (E), and studied (R)?
Why SPIDER?
SPIDER provides a more detailed breakdown of qualitative components than PEO, making it suitable for identifying studies that use diverse methodologies and focus on evaluation strategies.
4. PICOS – An Extension of PICO
Best for: Quantitative reviews where study design is a limiting factor.
P – Population
I – Intervention
C – Comparison
O – Outcome
S – Study design
Example: In children with asthma (P), does using an inhaler with a spacer (I) compared to a nebulizer (C) improve lung function (O) in randomized controlled trials (S)?
Why PICOS?
PICOS adds clarity when inclusion criteria are based on methodological quality, which is crucial for systematic reviews and meta-analyses.
5. PICo – For Qualitative Reviews
Best for: Reviews where the context rather than comparison is more relevant.
P – Population
I – Interest (phenomenon of interest)
Co – Context
Example: How do caregivers (P) perceive end-of-life care (I) in home-based settings (Co)?
Why PICo?
PICo is useful when exploring how context influences individual experiences or perceptions, especially in social or healthcare settings.
6. CIMO – For Organizational and Management Reviews
Best for: Reviews in business, management, education, and organizational contexts.
C – Context
I – Intervention
M – Mechanism
O – Outcome
Example: In public schools (C), how does performance-based pay (I) affect teacher motivation (M) and student performance (O)?
Why CIMO?
CIMO is ideal for realist reviews and policy-related questions that focus on how and why an intervention works (or doesn’t) in specific contexts.
Final Thoughts
Choosing the right framework is not about following a rigid template but about selecting a structure that best aligns with your review’s objective and evidence type. A well-structured research question not only guides your inclusion criteria and search strategy—it also shapes your data extraction, synthesis, and interpretation.
So, before you dive into databases or start screening articles, take time to carefully craft your research question using one of these established frameworks. It’s the foundation that your entire systematic review will rest upon.
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