An outcome measure, endpoint, effect measure or measure of effect is a measure within medical practice or research, (primarily clinical trials) which is used to assess the effect, both positive and negative, of an intervention or treatment.[1][2] Measures can often be quantified using effect sizes.[3] Outcomes measures can be patient-reported, or gathered through laboratory tests such as blood work, urine samples etc. or through medical examination.[1] Outcomes measures should be relevant to the target of the intervention (be it a single person or a target population).[2]
Depending on the design of a trial, outcome measures can be either primary outcomes, in which case the trial is designed around finding an adequate study size (through proper randomization and power calculation).[1] Secondary or tertiary outcomes are outcome measures which are added after the design of the study is finalized, for example when data has already been collected. A study can have multiple primary outcome measures.[1]
Outcome measures can be divided into clinical endpoints and surrogate endpoints where the former is directly related to what the goal of the intervention, and the latter are indirectly related.[1]