Once evidence is acquired, it is important to evaluate its level of evidence and quality. There are numerous scales for levels of evidence with some using three levels and some as many as seven. Which is the best level of evidence scale to use? There is a lack of standardization of the definitions of levels of evidence. Each scale needs to be carefully evaluated. Until standardization occurs, develop a rationale for selecting the scale you use. There are also different criteria used to determine the quality of the evidence. Review these examples of different scales and grading criteria. Several of the sources have additional information about evidence-based practice.