The definition of EBM states the importance of obtaining the "best available evidence." The evidence hierarchy is an attempt to rank the health information resource/study design with the highest quality sitting atop and the lower levels descending below. This hierarchy is helpful to guide evidence acquisition (literature searching) as well as providing clearer communication when discussing the landscape of health literature. When it comes to prioritizing the evidence in any specific situation, clinicians will need understand the nuances of the evidence (reviews, studies) obtained. It is not uncommon for lower levels of evidence on the hierarchy to provide better evidence that those sitting above: a hot-off the-press large RCT over an older meta analysis containing small studies.