Duration of untreated psychosis (DUP) is considered an important predictor of short-term clinical outcome. Early intervention in psychosis services aim to deliver effective intervention as close as possible to the emergence of psychosis, thereby reducing DUP and promoting early and enduring recovery.

Methodology: A literature review was conducted to explore the evolution of the concept of DUP, synthesise the evidence for its predictive value, compare instruments used to measure DUP and assess the psychometric properties of the Nottingham Onset Schedule (NOS) as a measure of DUP.

Identifying time points when psychosis emerges and remits are conceptually ambiguous and clinically difficult to ascertain. Most DUP measures do not take this ambiguity into account and introduce spurious precision in DUP measurements. Mean DUP therefore varies widely between studies, from 25 weeks to over 700 weeks. The relationship between long DUP and poor outcome is also confounded by an interaction between premorbid dysfunction, insidious onset, delayed help-seeking and poor clinical course. A new instrument, the Nottingham Onset Schedule (NOS) is a relatively simple, clinician friendly scale to measure DUP and has been well-validated.

A standardised measure of DUP is a vital first step to allow comparisons between studies. The NOS provides a standardised and reliable way of recording early changes in psychosis and identifies relatively precise time points for measuring several durations in emergent psychosis. Early intervention services can only reduce DUP if early detection is an inherent part of the service