This is a picture of a triangle with the following phrases starting at the base and working up by level. First Level: Case Reports, second level: Cross-Sectional Studies, Third Level: Case-Control Studies, Forth Level: Cohort Studies, Fifth Level: Randomized Controlled Trial (RTC) Without Definitive results, Sixth Level: Randomized Controlled Trial (RTC) With Definitive Results, Seventh: Systematic Reviews and Meta-Analyses