A well-formulated research question is the foundation of successful evidence synthesis.  Use of structured frameworks can be useful for refining and the question.  PICO is a widely known format used for question formulation in evidence-based practice, but there are others!  

• PICO (Population, Intervention, Comparison, Outcome) – for clinical/health sciences
• PEO (Population, Exposure, Outcome) – for public health or observational studies
• SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type) – for qualitative research focused on outcomes of a service or policy
• SPICE (Setting, Perspective, Intervention/Exposure, Comparison, Evaluation) - for qualitative research that evaluates outcomes of an intervention, service, or project
• ECLIPSE (Expectation, Client group, Location, Impact, Professionals, Service) - for health policy and management 

An example using the PICO format:

• P -- Adult Patients with heart failure
• I -- Remote monitoring of vital signs
• C -- Standard outpatient followup
• O -- Impact on hospital admission rates

Your question: In patients with heart failure, does remote monitoring of vital signs reduce hospital readmissions compared to standard outpatient follow-up?

Eligibility criteria are an extension of your research question and are essential for helping the research team select studies during the screening process.  This is essential for maintain consistency and transparency during the selection process.  Overly broad or vague criteria will make it difficult for the team to screen out studies that will be less relevant to the research question.   

The criteria you select will depend on your research topic and objectives.   Factors to consider:

• Population: Age, gender, health condition
• Intervention/Exposure: Type, duration, intensity
• Setting: location of patient or healthcare setting
• Study Design: RCTs, cohort studies, qualitative studies
• Outcomes: Specific outcomes relevant to your question
• Language: limiting language can introduce geographic bias, but is feasible in situations were time is limited or 
• Publication Date: feasible if it can be justified on when the treatment or condition emerged, or if a prior review is being updated