Appendix B
Definitions
If not otherwise indicated, data elements were defined according to the 2017–18 definitions in the National health data dictionary, versions 16, 16.1 and 16.2 (AIHW 2012, 2015a, 2015b).
Public hospital peer groups
Public hospital peer groups are used to classify hospitals that share similar characteristics, to provide a basis for meaningful comparisons.
This report presents analyses by hospital peer group, including the NHA performance indicators, using the AIHW’s peer group classification. The Steering Committee for the Review of Government Service Provision will also use these peer groups to report the NHA performance indicators in the Report on government services 2019.
Before 2014–15, this information was presented using the AIHW’s previous peer group classification. As a result, the data presented here by public hospital peer group are not directly comparable with those presented in AIHW reports before 2014–15.
See the AIHW publication Australian hospital peer groups (AIHW 2015c) for more information.
Data presentation
Data are presented by the state or territory of the hospital, not by the state or territory of usual residence of the patient.
Except as noted in this section, the totals in tables include data only for those states and territories for which data were available, as indicated in the tables. Throughout the report, percentages may not add up to 100.0 because of rounding. Percentages and rates shown as 0.0 or 0 indicate a zero. The symbol ‘<0.1’ has been used to denote less than 0.05, but greater than 0.
Data on waiting times (50th and 90th percentiles) and the proportion seen on time have been suppressed if there were fewer than 100 presentations in the category being presented. The abbreviation ‘n.p.’ has been used to denote these suppressions. For these tables, the totals include the suppressed information.
Changes over time
Time series data in this report show average annual changes from 2013–14 to 2017–18, and the annual change between 2016–17 and 2017–18.
Median and 90th percentiles
The 50th percentile (the median, or the middle value in a group of data arranged from lowest to highest value for minutes waited) represents the number of minutes within which 50% of patients commenced clinical care (or completed their episode, or were admitted)—half the waiting times will have been shorter, and half longer than the median.
The 90th percentile data represent the number of minutes (or hours and minutes) within which 90% of patients commenced clinical care (or completed their episode, or were admitted).
The 50th percentile and 90th percentile waiting times are calculated using an empirical distribution function with averaging. Using this method, observations are sorted in ascending order.
The calculation is where:
n is the number of observations, and
p is the percentile value divided by 100,
then n × p= i + f (where i is an integer and f is the fractional part of n × p).
If n × p is an integer, the percentile value will correspond to the average of the values for the ith and (i+1)th observations.
If n × p is not an integer, the percentile value will correspond to the value for the (i+1)th observation.
For example, if there were 100 observations, the median waiting time will correspond to the average waiting time for the 50th and 51st observations (ordered according to waiting time). Similarly, the 90th percentile will correspond to the average waiting time for the 90th and 91st observations if there are 100 observations.
If there were 101 observations, the median waiting time will correspond to the waiting time for the 51st observation, and the 90th percentile waiting time will correspond to the waiting time for the 91st observation.
The 50th and 90th percentiles have been rounded to the nearest whole number of minutes.
Principal diagnosis reporting
For the 2017–18, diagnosis information was reported for the NNAPEDCD using the following classifications:
- Systematized Nomenclature of Medicine—Clinical Terms—Australian version, Emergency Department Reference Set.
- International Classification of Diseases, 9th Revision, Clinical Modification (ICD‑9‑CM), 2nd edition.
- International Classification of Diseases and Related Health Problems, 10th Revision, Australian Modification (ICD‑10‑AM) 6th, 7th, 8th, 9th or 10th editions.
The AIHW mapped all diagnosis information to a single classification.
Method of mapping provided diagnosis codes to a single classification
The AIHW used mapping files to assign diagnosis information provided in the different classifications to a single classification (to 3‑character categories in ICD‑10‑AM 10th edition). This mapping involved the use of:
- ICD‑9‑CM to ICD‑10‑AM historical mapping files
- ICD‑10‑AM to ICD‑10‑AM edition mapping files
- SNOMED CT‑AU (EDRS) to ICD‑10‑AM 6th edition mapping file.
Step 1: mapping SNOMED‑CT‑AU EDRS to ICD‑10‑AM 6th edition
Establishments that used SNOMED‑CT‑AU EDRS provided 2.2 million presentations.
The principal diagnosis data coded in SNOMED‑CT‑AU EDRS were mapped to ICD‑10‑AM 6th edition codes using a mapping file provided by the Independent Hospital Pricing Authority.
About 3,000 presentations with valid SNOMED‑CT‑AU EDRS codes did not map to an ICD‑10‑AM 6th edition diagnosis code. These corresponded to about 850 unique SNOMED‑CT‑AU EDRS codes that contained concepts that did not have equivalent codes in ICD‑10‑AM (for example, dressing of wound, preparation of medical certificate, and patient left against medical advice).
The principal diagnoses for the remaining presentations were mapped to 2,749 unique ICD‑10‑AM 6th edition codes. Following the mapping, a relatively small number of ICD‑10‑AM 6th edition diagnosis codes were mapped to ICD‑10‑AM 10th edition.
Step 2: assigning ICD‑10‑AM codes to diagnosis data provided in ICD‑9‑CM
About 34,400 presentations provided by establishments reported coding diagnoses using ICD‑9‑CM. Of these, about 4,900 records did not have a valid ICD‑9‑CM code—the majority had truncated ICD‑9‑CM codes (for example, an invalid 3‑digit code was provided for a condition that required a 4‑digit code). The principal diagnoses for the remaining 29,500 presentations were mapped to ICD‑10‑AM codes, and were subsequently mapped to ICD‑10‑AM 10th edition.
Step 3: assigning ICD‑10‑AM 10th edition codes for records provided using ICD‑10‑AM
More than 5.2 million presentations provided by establishments reported coding diagnoses using ICD‑10‑AM 6th, 7th, 8th, 9th and 10th editions.
The majority of diagnosis codes in the 6th, 7th, 8th and 9th editions were the same as the corresponding diagnosis codes in ICD‑10‑AM 10th edition. A small number of diagnosis codes were mapped to the 10th edition.
Step 4: assessment of completeness of mapping
Following mapping, about 96% of principal diagnoses were mapped to valid ICD‑10‑AM 10th edition diagnosis codes.
Waiting times
Waiting time to commencement of clinical care
The waiting times are determined as the time elapsed between presentation to the ED and the commencement of clinical care. The calculation is restricted to presentations with a type of visit of Emergency presentation, and presentations were excluded if the waiting time was missing or invalid, or if the patient Did not wait to be attended by a health care professional, or was Dead on arrival.
See data quality statement for information on the completeness of the data provided for waiting times calculations.
Proportion of presentations seen on time
The proportion of presentations seen on time was determined as the proportion of presentations in each triage category with a waiting time less than or equal to the maximum waiting time stated in the Australasian Triage Scale definition.
For this report, a patient with a triage category of Resuscitation was considered to be seen on time if the waiting time to commencement of clinical care was less than or equal to 2 minutes.
The calculation is restricted to presentations with a type of visit of Emergency presentation, and presentations were excluded if the waiting time was missing or invalid, if the patient Did not wait to be attended by a health care professional, or was Dead on arrival, or if the triage category was not reported.
Proportion of presentations ending in admission
The proportion of presentations ending in admission is determined as the proportion of all emergency presentations with an episode end status of Admitted to this hospital (either short‑stay unit, hospital‑in‑the‑home, or non‑emergency department hospital ward) (for the NAPEDC NMDS), or Transferred for admitted patient care in this hospital (either short‑stay unit, hospital‑in‑the‑home, or non‑emergency department hospital ward) (for the NAPEDC NBEDS). The calculation is restricted to presentations with a type of visit of Emergency presentation.
Emergency department length of stay
Emergency department length of stay
The length of stay is determined as the time elapsed between presentation and the physical departure of the patient. Length of stay statistics are calculated for all ED type of visit categories.
Proportion of presentations completed in 4 hours or less
The proportion of presentations completed in 4 hours or less is determined as the proportion of all emergency presentations for which the time elapsed between the presentation and the physical departure of the patient was less than or equal to 240 minutes.
Presentations were excluded if either (or both) of the presentation date/time or physical departure date/time were missing or invalid, or if the calculation resulted in an invalid length of stay (that is, missing or a negative number of minutes).
Admission to hospital from emergency departments
Admission to hospital from EDs (for patients who were subsequently admitted) is calculated using the ED length of stay for presentations with an episode end status of Admitted to this hospital (either short‑stay unit, hospital‑in‑the‑home, or non‑emergency department hospital ward) (for the NAPEDC NMDS), or Transferred for admitted patient care in this hospital (either short‑stay unit, hospital‑in‑the‑home or non‑emergency department hospital ward) (for the NAPEDC NBEDS).
Duration of clinical care
The duration of clinical care is determined as the time elapsed between commencement of clinical care and the end of the non‑admitted patient ED episode (the end of clinical care).
See the data quality statement for information on the completeness of the data used to calculate the duration of clinical care. Duration of clinical care statistics are calculated for presentations with a type of visit of Emergency presentation.
Age and sex of patient
All states and territories supplied the date of birth of the patient, from which the age of the patient at the date of presentation was calculated.
For 317 records, the age of the patient could not be calculated, as date of birth was missing. For 567 records, the sex of the patient was reported as either Intersex or indeterminate or Not stated/inadequately described.
Age-standardised rates
Unless noted otherwise, population rates (presentation rates) presented in this report are age-standardised, calculated using the direct standardisation method and 5 year age groups.
The ABS’ population estimates for 30 June at the beginning of the reporting period were used for the observed rates.
For time series tables in this report, the age-standardised presentation rates (per 1,000 population) have been calculated using estimated resident populations relevant to the reporting period.
The total Australian population for 30 June 2001 was used as the standard population against which expected rates were calculated.
There was some variation in the age group used for age-standardising. For example:
- presentation rates by hospital state, remoteness areas and by quintiles of socioeconomic advantage/disadvantage (SES) were directly age-standardised, using the estimated resident populations as at 30 June 2017. The estimated resident populations had a highest age group of 85 and over
- presentation rates by Indigenous status were directly age-standardised, using the projected Indigenous population (low series) as at 30 June 2017. The population for other Australians was based on the estimated resident populations as at 30 June 2017. As the projected Indigenous population estimates had a highest age group of 65 and over, standardised rates calculated for analyses by Indigenous status are not directly comparable with other standardised rates presented in this report which used a highest age group of 85 and over.
Presentation rate ratios
For some tables reporting comparative presentation rates, presentation rate ratios are presented. These ratios are calculated by dividing the age-standardised presentation rate for a population of interest (an observed rate) by the age-standardised presentation rate for a comparison population (the expected rate). The calculation is as follows:
Presentation rate ratio = observed rate/expected rate
A rate ratio of 1.0 indicates that the population of interest (for example, Indigenous Australians) had a presentation rate similar to that of the comparison group (for example, other Australians). A rate ratio of 1.2 indicates that the population of interest had a rate that was 20% greater than that of the comparison population and a rate ratio of 0.8 indicates a rate 20% smaller.
The populations used for the observed and expected rates vary in this report. For example for:
- Indigenous status, the rate ratio is equal to the presentation rate for Indigenous Australians divided by the presentation rate for other Australians (other Australians includes Indigenous status not reported)
- analyses by state or territory of residence, remoteness areas and SES of area of residence, the rate ratio is equal to the presentation rate for the state or territory of residence, remoteness area, or SES group, divided by the presentation rate for Australia.
References
AIHW (Australian Institute of Health and Welfare) 2012. National health data dictionary 2012 version 16. Cat. no. HWI 119. Canberra: AIHW.
AIHW 2015a. National health data dictionary: version 16.1. National health data dictionary no. 17. Cat. no. HWI 130. Canberra: AIHW. Viewed 20 September 2018.
AIHW 2015b. National health data dictionary: version 16.2. National health data dictionary no. 18. Cat. no. HWI 131. Canberra: AIHW. Viewed 20 September 2018.
AIHW 2015c. Australian hospital peer groups. Health services series no.66. Cat. no. HSE 170. Canberra: AIHW.