Not all scientific studies are created equal! Study design can impact the strength and quality of evidence that a study holds. This 'Evidence Pyramid' depicts the levels of evidence provided by different types of studies and information. The wide base of the pyramid indicates that there are many editorials and expert opinions, but that they provide the weakest evidence to inform policy and decision-making. There are many fewer systematic reviews on a topic, but these represent the pinnacle of research evidence.
The PICO Framework can be used to structure and refine your research question. This can then be used to structure your search strategy and your process for identifying articles of interest.