A COA is any assessment that may be influenced by human choices, judgment, or motivation and may support either direct or indirect evidence of treatment benefit. Unlike biomarkers that rely completely on an automated process or algorithm, COAs depend on the implementation, interpretation, and reporting from a patient, a clinician, or an observer. The four types of COAs are patient-reported outcome (PRO) measures, clinician-reported outcome (ClinRO) measures, observer-reported outcome (ObsRO) measures, and performance outcome (PerfO) measures. Some clinical outcomes used in clinical research belong to more than one category.

FYI: Classification by the FDA



Patient-reported outcomes (PRO)

A PRO is any report of the status of a patient’s health condition that comes directly from the patient, without interpretation of the patient’s response by a clinician or anyone else. ". Common PROs include the MD Anderson Symptom Inventory (MDASI), which is used frequently in oncology, and the EORTC QLQ-C30, which is used for QOL evaluation.

Definition by the FDA
A PRO is a measurement based on a report that comes from the patient (i.e., study subject) about the status of a patient’s health condition without amendment or interpretation of the patient’s report by a clinician or anyone else. A PRO can be measured by self-report or by interview, provided that the interviewer records only the patient’s response. Symptoms or other unobservable concepts known only to the patient (e.g., pain severity or nausea) can only be measured by PRO measures. PROs can also assess the patient perspective on functioning or activities that may also be observable by others.

For details about PRO (external link)

Clinician-reported outcomes (ClinRO)

While PROs are direct responses from patients, a ClinRO reflects the evaluation of a patient's health condition by a healthcare professional. The ECOG Performance Status and Common Terminology Criteria for Adverse Events (CTCAE) are commonly used in oncology.

Definition by the FDA
A ClinRO is based on a report that comes from a trained health-care professional after observation of a patient’s health condition. A ClinRO measure involves a clinical judgment or interpretation of the observable signs, behaviors, or other physical manifestations thought to be related to a disease or condition. ClinRO measures cannot directly assess symptoms that are known only to the patient (e.g., pain intensity).

For details about ClinRO (external link)

Observer-reported outcomes (ObsRO)

An ObsRO is a measurement based on an observation by someone other than the patient or a health professional.  For example, the Pediatric Quality of Life Inventory™ is a representative ObsRO for pediatric patients. In addition, the Edmonton Symptom Assessment System Revised (ESAS-r) is commonly used in oncology as either an ObsRO or PRO.

Definition by FDA
An ObsRO is a measurement based on an observation by someone other than the patient or a health professional. This may be a parent, spouse, or other non-clinical caregiver who is in a position to regularly observe and report on a specific aspect of the patient’s health. An ObsRO measure does not include medical judgment or interpretation. Generally, ObsROs are reported by a parent, caregiver, or someone who observes the patient in daily life. For patients who cannot respond for themselves (e.g., infants or cognitively impaired), we encourage observer reports that include only those events or behaviors that can be observed. As an example, observers cannot validly report an infant’s pain intensity (a symptom) but can report infant behavior thought to be caused by pain (e.g., crying). For example, in the assessment of a child’s functioning in the classroom, the teacher is the most appropriate observer. Examples of ObsROs include a parent report of a child’s vomiting episodes or a report of wincing thought to be the result of pain in patients who are unable to report for themselves.

For details about ObsRO (external link)

Performance outcomes (PerfO)

PerfOs are used to evaluate the performance of a patient conducting tasks as instructed by a healthcare professional. For example, in a 6-minute walk test, a patient walks for 6 minutes under the instruction of a healthcare professional, and the distance the patient walked is measured as a performance outcome.

Definition by FDA
A PerfO is a measurement based on a task(s) performed by a patient according to instructions that is administered by a health care professional. Performance outcomes require patient cooperation and motivation. These include measures of gait speed (e.g., timed 25 foot walk test), memory recall, or other cognitive testing (e.g., digit symbol substitution test).

For details about PerfO (external link)