We will therefore be focusing on the validity of a triage tool rather than its reliability.

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A patient's acuity level is defined as the urgency for effective care.

In the ED triage setting effective care is defined as the provision of an intervention or treatment that reduces the patient's urgency for care or prevents clinical deterioration.

Emergency department (ED) triage is the process of sorting and filtering patients based on medical priority.

It aims to determine a patient's acuity level in order to facilitate timely and effective care before their condition worsens.

This illustration of triage is a highly simplified approach to a complex set of interrelationships.

It is acknowledged that additional variables may influence optimal time to care and effectiveness of care significantly (such as variability in triage nurse decisions).‐rater reliability assesses the variability within a single triage officer re‐rating the same patient.

Particular outcomes, or events with time‐ordering, are selected as surrogate markers (such as mortality rates, hospital admission rates, resource utilisation, and length of stay in hospital).

There are methodological problems with the use of this type of validity as it does not always answer the core question: “Is the triage instrument able to measure what is supposed to be measured?

During any validity testing an important distinction needs to be made between internal validity (which refers to inferences about the source population), and external validity (whether inferences may be generalised to people outside the source population).

A triage tool designed for a developed country may be valid in that context, leading to favourable results that are meaningful and have implications for action.

South Africa has adapted the Modified Early Warning Score (MEWS) as the South African Triage Scale after validating it on the local national population.