Glossary · Outcomes and measurementUpdated September 28, 2026

PRO, ClinRO, ObsRO and PerfO: the four types of COA

A clinical outcome assessment (COA) measures how a patient feels, functions or survives. There are four types, defined by who provides the information: the patient, a clinician, an observer, or the patient's performance on a task.

  • COA types in plain language
  • How it works in practice
  • Related terms

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PRO

Patient-reported

Participant, own phone

ObsRO

Observer-reported

Caregiver

ClinRO

Clinician-reported

Site staff, clinic tablet

PerfO

Performance outcome

Site-run test, e.g. chair rise

The four types

COA types with examples

TypeWho reportsExamples
PRO: patient-reported outcomeThe patient, without interpretation by anyone elsePHQ-9, EQ-5D, DLQI, PRO-CTCAE
ClinRO: clinician-reported outcomeA trained clinician using judgementC-SSRS, ADAS-Cog, rating scales
ObsRO: observer-reported outcomeSomeone who observes the patient, such as a parent or caregiverCaregiver-reported behaviours, infant symptoms
PerfO: performance outcomeThe patient performs a standardised taskSix-minute walk test, timed up and go

In short

  • The type depends on whose judgement produces the score, not on the device or setting.
  • ObsRO is for observable behaviours only; observers should not report the patient's feelings, which only the patient can report.
  • Collecting COAs electronically is called eCOA; ePRO is the patient-reported subset.
  • Regulators expect COAs used as endpoints to be fit for purpose in the target population.

In Capture

Every assessment records who completes it

In Capture each assessment on the schedule is set to be completed by the participant (PRO), a caregiver (ObsRO) or site staff (ClinRO, and PerfO tests built as site forms). The same form works on a participant's phone, a home tablet or a clinic device, and licensed instruments carry their licence details.

  • PRO, ObsRO, ClinRO and PerfO in one study.
  • Browser-based, no app.
  • Licence tracking on licensed instruments.
eCOA software for clinical trials
Clinic tablet · landscape5 of 12

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FAQ

Common questions

Something not covered here? Ask us directly.

What is a clinical outcome assessment?

A measure of how a patient feels, functions or survives, reported by the patient, a clinician, an observer, or through task performance.

What is the difference between ObsRO and PRO?

A PRO comes from the patient. An ObsRO comes from someone who observes the patient, such as a caregiver, and covers observable behaviours rather than feelings.

Is a six-minute walk test a PRO?

No. It is a performance outcome (PerfO): the patient performs a standardised task.

What is eCOA?

Electronic collection of clinical outcome assessments. ePRO is its patient-reported subset.

All four COA types in one study

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