An Introduction to Clinical Outcome Assessments (COAs)

In clinical research, a fundamental question is “How do we show whether a medical product works and is safe?” Clinical outcome assessments, commonly referred to as COAs, help answer this question. 

A clinical outcome assessment is any measure that reflects or describes how a patient feels, functions or survives. Depending on the study, COAs may also be called: 

  • Questionnaires 
  • Surveys 
  • Instruments 
  • Scales 
  • Diaries 

No matter the name, COAs are foundational tools in clinical trials. 

Why Clinical Outcome Assessments Matter in Clinical Trials 

COAs influence nearly every stage of a study — from determining who can participate to judging the safety and effectiveness of a treatment. 

Eligibility Criteria 

COAs may be part of inclusion or exclusion criteria, ensuring that participants are suitable for the study. 

Efficacy Endpoints 

COAs often serve as primary, secondary or exploratory endpoints that determine whether an intervention has had the intended effect. 

Safety Endpoints and Monitoring 

COAs often serve as safety endpoints in trials, and can also be used throughout the study to evaluate safety signals and monitor whether it is safe for a participant to continue in the trial. 

Reimbursement Decisions 

After a product reaches market, COA data can be used to support health-technology assessments and reimbursement decisions. 

Clinical Outcome Assessment Examples 

COAs are grouped into four major categories, each designed to capture a different perspective of a patient’s experience.  

An infographic centered on "COAs" (Clinical Outcome Assessments) with four branching categories: ClinRO: Defined as Clinician-reported outcome. PRO: Defined as Patient-reported outcome. PerfRO: Defined as Performance outcome. ObsRO: Defined as Observer-reported outcome.

Clinician-Reported Outcomes (ClinRO) 

A ClinRO is a measurement completed by a trained healthcare professional following direct observation, interview or physical examination of a participant. 

Clinicians may evaluate: 

When Are ClinROs Appropriate? 

ClinROs are ideal for conditions requiring expert assessment, such as: 

They are also important when patients cannot reliably self-report due to: 

Common ClinRO Instruments 

Patient-Reported Outcomes (PRO) 

A patient-reported outcome captures information directly from the patient, without interpretation from clinicians or caregivers, and are advised when measuring concepts best known by the patient themselves. 

Today, PROs are routinely used as endpoints in clinical trials to elicit the patient perspective​, ensuring greater patient focus on medical product development, and providing the opportunity to measure concepts that matter to the patient to really understand the value and treatment benefit (or risk) of a product. ​ 

Patients may complete PROs independently or via interview (as long as responses are recorded verbatim, and the interviewer does not add their own interpretation​). 

What Do PROs Measure? 

PROs often assess: 

A central dark blue circle labeled 'Quality of Life' is surrounded by ten smaller white circles connected by lines. The surrounding factors include: Environmental Quality, Financial Conditions, Social Support, Cultural Factors, Health and Social Services, Health, Leisure Activities, Life Satisfaction, Social Interactions, and Functional Abilities

Common PRO Instruments Quality of Life Measures

Event-Driven or Daily Reporting

When Should PROs Be Used?

Use PROs when:

Observer-Reported Outcomes (ObsRO)

An ObsRO is reported by someone who regularly observes the patient — typically a parent or caregiver. It focuses only on observable behaviors or events, without medical judgment or interpretation.

ObsROs are particularly valuable for:

ObsRO Examples

Quality of Life

Event Reporting

Behavioral Measures

ObsROs are distinct from proxy-reported outcomes. Proxy-reported outcome measures involve someone other than the patient reporting on the patient experience as if they were the patient. These are strongly discouraged by regulatory bodies, because they are measuring concepts only known to the patients themselves, and are not necessarily a true reflection of how the patient feels or functions.

Concepts that are only known by the patient (e.g., pain, symptoms, feelings), should be measured by a PRO, or observable behavior by an ObsRO.

What Is a Proxy-Reported Outcome?

An infographic comparing three types of clinical outcome assessments: ObsRO, Proxy-reported, and PRO. ObsRO: Defined as completed by someone other than the participant based on observable signs, events, or behaviors. Example: “Based on what you observed... please rate the severity of your child’s abdominal pain-related signs today (such as crying, holding stomach or abdomen).” Proxy-reported: Defined as completed by someone other than the participant who is reporting on behalf of the participant as if they were the participant. Example: “How severe was your child’s pain from the time your child woke up until now?” PRO: Defined as responses reported by the participant without influence, interpretation, or amendment. Example: “How severe was your pain today?

Performance-Reported Outcomes (PerfO)

A PerfO is based on a standardized task that a patient performs, typically under structured conditions.

May be administered by an appropriately trained individual or completed by patient independently.​

These tasks assess:

PerfOs may require equipment such as:

Common PerfO Measures Cognitive Tests

Physical Performance

The Value of Clinical Outcome Assessments

Clinical outcome assessments are crucial tools that bring patient experience, clinical expertise and measurable performance together. Whether reported by clinicians, patients, caregivers or demonstrated through performance tests, COAs provide rich insights into the real impact of medical products.

By using the right COA at the right time, clinical trials can more accurately capture what matters most to patients. Electronic data capture is a robust way to capture COA data — find out more about the benefits here.