The levels of evidence are assigned to studies based on the quality of design validity and applicability To care the patient live decisions give the strength of recommendation.
Level 1:, evidence from Systematic review ,meta analysis of relevant trials evidence-based clinical practice guidelines of good quality have similar results
level 2 evidence obtained from well designed randomised controlled trials
level 3 evidence obtained from unrandomised well designed controlled trials
level 4 evidence obtained from cohort studies
level 5 evidences obtained from systematic reviews of descriptive and qualitative studies l
level 6 evidence and from single qualitative study
level 7 evidences obtained from opinion other expert committee.
While searching for evidence based information the highest level of evidence possible Systematic reviews should be selected information that has not been critically appraised should be considered unfiltered.
As remove up the pyramid your studies are available and we need to move down if our quest for resources at the top of the pyramid is un successful.
Levels of evidence provide the strength of recommendation for a particular treatment the most visible in practice guidelines toHealth Care professionals too quickly decide the importance of a recommendation in any given guideline.
For example the systematic review of meta-analysis of randomised controlled trials are at the top of the pyramid under typically the highest level of evidence because the study design reduces probability of buyers where as the weakest level of evidence is the opinion collected from other expert committees.
Sometimes strong recommendation can also be made from lower levels of evidence based on the situation.