Refers to the use of evidence, for example from natural scientific or medical studies, as a base for public recommendations, e.g. of the RKI. There are different levels of evidence:
Level I a: Evidence from at least one systematic review of well-designed randomised clinical trials (RCTs).
Level I b: Evidence from at least one well-designed RCT.
Level II a: Evidence from a well-designed trial without randomisation.
Level II b: Evidence from at least one well-designed trial of another type of quasi-experimental studies.
Level III: Evidence from more than one well-designed non-experimental trials.
Level IV: Evidence from opinions and convictions of authorities (from clinical experience); expert commissions; descriptive studies.