When you’ve found supporting research for a topic, it’s good to know how much weight to give it in determining its validity. This pyramid shows a good criterion for doing that. Keep in mind that depending on the topic being studied, certain types of studies that are lower on the pyramid may provide better evidence than upper-tier ones. It’s not absolute, nor does it definitively rule lower-tier evidence as superfluous. It’s just a really good place to start for a standard of quality.
Notice how “anecdotes” are not on the pyramid, not even at the bottom? You may have 1,000’s of testimonials to a certain treatment, but you know what they say: the plural of anecdote is not evidence.