Systematic Reviews seek to answer a specific research question. There are question formation frameworks to help you formulate a focused research question.
PICO is the most common question formation framework for systematic reviews.
PICO works well for clinical and quantitative research topics (therapy, diagnosis, prognosis, etiology/harm, and prevention questions)
PICO questions identify 3-4 concepts: patient/population/problem, intervention, comparison (optional), and outcome