As the complexity of studies and the size of the knowledge base for healthcare continues to expand, the need to define the worthiness of evidence became apparent. The consensus among scientists led to the creation of seven levels of evidence that assist with selecting the best possible studies for advancing healthcare. Evidence of the highest quality comes from studies that examine and compile information from a multitude of randomized clinical trials (RCTs) (Fain, 2017). Clinical trials are highly valued as evidence, falling just one or two positions behind systematic reviews, depending on randomization efforts of their authors, due to their limited scope (Fain, 2017). The design of these studies plays a crucial role in their qualities, as common pitfalls for gathering research data that are present in other types of studies can cause limitations, such as poorly generalizable results.
The following levels may be too narrow, yet they are still vital for specific cases and arguments. Case-control and cohort studies take the fourth level since their outcomes provide valuable evidence from investigations that may shed light on particular deficiencies or missed opportunities for improving specific guidelines (Fain, 2017). Systematic reviews of studies that are strictly observational are placed on the fifth level due to their value as a compilation of information, yet sources are prone to being heavily limited (Fain, 2017). Data from a single study is often counted as insufficient by itself and takes the sixth level of evidence (Fain, 2017). The last level of evidence is data based on opinions of experts and authorities with little to no support from data included in the study (Fain, 2017). In conclusion, the seven levels of evidence allow scientists to categorize the studies to understand their value as a foundation for future research and assess real-world applicability.
Reference
Fain, J. A. (2017). Reading, understanding, and applying nursing research (5th ed.). F. A. Davis Company.