[3] The first recorded EWS was developed by a team in James Paget University Hospital, Norfolk, United Kingdom, and presented at the May 1997 conference of the Intensive Care Society.

[2] Early warning systems are typically designed based on statistical analysis of the degree of variation in any given observation (such as vital signs, consciousness or demographics), and corresponding associations with adverse events (such as ICU admission, cardiac arrest, or death).

[6] EWSs generate an overall score intended to indicate the risk of a patient experiencing an adverse outcome, such as requiring ICU admission, cardiac arrest, or in-hospital death.

[6] Throughout the world the EWS is based on the principle that clinical deterioration can be seen through changes in multiple physiological measurements, as well as large changes within a single variable.

[8] This has led to a call in several countries for the development of a national early warning score that would allow a standardised approach to assessing and responding to deteriorating patients.

Chart design, such as the use of colours, has a statistically significant effect on the speed and accuracy of identifying abnormal observations.

For example, the Queensland Adult Deterioration Detection System includes "Modified Calling Criteria" that allow senior medical officers to authorise changes to the normal observation ranges for a patient.

[2] A 2021 Cochrane review of EWSs found that there is only low certainty in the quality of research on these systems, and that the evidence may indicate little to no difference in patient outcomes; no recommendations could be concluded in either regard.

For example, a lack of clinician knowledge of the EWS, incomplete or incorrect vital sign measurement, and the influence of power between nursing and medical staff hinder detection of clinical deterioration.

[3] A range of Early Warning Scores have been developed in response to the needs of specific patient types (e.g. PEWS for children) or to support local best practice (NEWS in the UK).

The revised version was optimised for the identification of sepsis, alternative oxygen targets in people with underlying lung disease, and the onset of delirium.

[23] The Australian Commission on Safety and Quality in Health Care has also released the National Consensus Statement: Essential elements for recognising and responding to acute physiological deterioration.