PICO as used in EBP

1-What does PICO mean, and how is this used in EBP?
2-What are the characteristics of level 3 evidence?
3-What key words might you use when searching a database such as pubmed for information on orthokeratology for correction of myopia in children?
4-What factors in study design can cause bias?-
5-What are the differences between internal and external validity?
6-What is meant by “clinical expertise” as one of the components of EBP?
7-What is the difference between high and low level evidence?
8-In evidence-based practice, what factors form the basis of a clinical decision