Key concepts

Overnight admitted mental health-related care
Key concept Description
Average length of stay Average length of stay is the average number of patient days for admitted patient separations.
Care type

The care type defines the overall nature of a clinical service provided to an admitted patient during an episode of care (admitted care), or the type of service provided by the hospital for boarders or posthumous organ procurement (other care).

Mental health related

A separation is classified as mental health-related for the purposes of this report if:

  • it had a mental health-related principal diagnosis, which, for admitted patient care in this report, is defined as a principal diagnosis that is either:
    • a diagnosis that falls within the section on Mental and behavioural disorders (Chapter 5) in the International Statistical Classification of Diseases and Related Health Problems, 10th revision, Australian Modification (ICD-10-AM) (codes F00–F99), or
    • a number of other selected diagnoses (see the technical information) for a full list of applicable diagnoses), and/or
  • it included any specialised psychiatric care.
Overnight admitted patient care

For this report overnight admitted patient separations refers to those separations when a patient undergoes a hospital’s formal admission process, completes an episode of care, is in hospital for more than one day and ‘separates’ from the hospital. Same-day separations are reported separately in the Admitted patient care – same-day care section of this report.

Patient day

Patient day means the occupancy of a hospital bed (or chair in the case of some same day patients) by an admitted patient for all or part of a day. The length of stay for an overnight patient is calculated by subtracting the date the patient was admitted from the date of separation and deducting days the patient was on leave. A same-day patient is allocated a length of stay of 1 day. Patient day statistics can be used to provide information on hospital activity that, unlike separation statistics, account for differences in length of stay. The patient day data presented in this report include days within hospital stays that occurred before 1 July provided that the separation from hospital occurred during the relevant reporting period (that is, the financial year period). This has little or no impact in private and public acute hospitals, where separations are relatively brief, throughput is relatively high and the patient days that occurred in the previous year are expected to be approximately balanced by the patient days not included in the counts because they are associated with patients yet to separate from the hospital and therefore yet to be reported. However, some public psychiatric hospitals provide very long stays for a small number of patients and, as a result, would have comparatively large numbers of patient days recorded that occurred before the relevant reporting period and may not be balanced by patient days associated with patients yet to separate from the hospital.

Principal diagnosis

The principal diagnosis is the diagnosis established after study to be chiefly responsible for occasioning the patient’s episode of admitted patient care.


Procedure refers to a clinical intervention that is surgical in nature, carries an anaesthetic risk, requires specialised training and/or requires special facilities or services available only in an acute care setting. Procedures therefore encompass surgical procedures and non-surgical investigative and therapeutic procedures, such as X-rays. Patient support interventions that are neither investigative nor therapeutic (such as anaesthesia) are also included.

Procedures are grouped together in blocks (Procedure blocks) based on the area of the body, health professional or intervention involved.

Psychiatric care days

Psychiatric care days are the number of days or part days the person received care as an admitted patient in a designated psychiatric unit or ward. 


Separation is the term used to refer to the episode of admitted patient care, which can be a total hospital stay (from admission to discharge, transfer or death) or a portion of a hospital stay beginning or ending in a change of type of care (for example, from acute care to rehabilitation). ‘Separation’ also means the process by which an admitted patient completes an episode of care by being discharged, dying, transferring to another hospital or changing type of care. Each record includes information on patient length of stay. A same-day separation occurs when a patient is admitted and separated from the hospital on the same date. An overnight separation occurs when a patient is admitted to and separated from the hospital on different dates. The numbers of separations and patient days can be a less reliable measure of the activity for establishments such as public psychiatric hospitals, and for patients receiving care other than acute care, for which more variable lengths of stay are reported.

Specialised psychiatric care

A separation is classified as having specialised psychiatric care if the patient was reported as having one or more days in a specialised psychiatric unit or ward.

Without specialised psychiatric care

A separation is classified as without specialised psychiatric care if the patient did not receive any days of care in a specialised psychiatric unit or ward. Despite this, these separations are classified as mental health related because the reported principal diagnosis for the separation is either one that falls within the Mental and behavioural disorders chapter (Chapter 5) in the ICD-10-AM classification (codes F00–F99) or is one of a number of other selected diagnoses (see the technical information).