Appendix B: Technical notes
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) (summarised in the Glossary).
Data are presented by the state or territory of the hospital, not by the state or territory of usual residence of the patient. 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 printed as 0.0 or 0 generally indicate a zero; the symbols ‘<0.1’ and ‘>–0.1’ are used to denote numbers between zero and 0.05 and zero and negative 0.05, respectively.
Data on 50th and 90th percentile waiting times and the proportion of patients who waited more than 365 days for their surgery have been suppressed if there were fewer than 100 admissions 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.
Clinical urgency categorisation
The ‘overdue wait’ is the amount of time spent waiting while overdue—that is, after 30, 90 or 365 days for clinical urgency categories 1, 2 and 3, respectively. The average overdue wait time (in days) is calculated for patients who were still waiting for their elective surgery as at 30 June 2018, who were ready for care, and who had waited beyond the recommended time.
In general, at the time of being placed on the public hospital waiting list, a clinical assessment is made of the urgency with which the patient requires elective surgery. The clinical urgency categories are:
Category 1—procedures that are clinically indicated within 30 days
Category 2—procedures that are clinically indicated within 90 days
Category 3—procedures that are clinically indicated within 365 days.
Analyses of clinical urgency category data have shown notable variation in the assignment of these categories, both among and within jurisdictions, and for individual surgical specialties and surgical procedures, as well as overall (See Appendix A).
50th and 90th percentile waiting times
The number of days a patient waits for elective surgery is calculated by states and territories as the number of calendar days between the date the patient was placed on the waiting list and the date that the patient was removed from the waiting list (the removal date), minus any days when the patient was ‘not ready for care’, and any days when the patient was waiting with a clinical urgency category that was less urgent than their clinical urgency category at removal (that is, if the patient’s urgency category was reassigned as being more urgent while they were waiting).
The number of days waited also does not include the time waited for an initial appointment with the specialist—from the time of referral by the patient’s GP—because this information is not available. The AIHW is currently working with states and territories to develop a consistent and nationally agreed approach to measuring access time for elective surgery from the time of referral by the patient’s GP. The aim is that nationally consistent data will become available on the time spent between GP referral and the initial specialist appointment.
The waiting times data presented in this report are for patients who completed their wait and were admitted for their surgery as either an elective or emergency admission.
In reports before 2011–12, waiting times information was presented for elective admissions only. Therefore, the data presented are not directly comparable with those presented in Australian hospital statistics reports before 2011–12.
The 50th percentile (the median or middle value in a group of data arranged from lowest to highest value) represents the number of days within which 50% of patients were admitted for the awaited surgery; half the waiting times will have been shorter, and half the waiting times longer, than the median.
The 90th percentile data represent the number of days within which 90% of patients were admitted for the awaited surgery. The remaining 10% of patients waited longer.
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 50th and 90th percentiles have been rounded to the nearest whole number of days.
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 ascending waiting time). Similarly, the 90th percentile waiting time 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.
Changes over time
Tables presenting the numbers of admissions from elective surgery waiting lists over time show the average annual changes from 2013–14 to 2017–18 and from 2015–16 to 2017–18. Where noted in the text, rates were adjusted for changes in data coverage over time, as described below in ‘Estimated coverage of the NESWTDC’.
See the pdf report for detailed information on the calculation of changes over time.
Estimated coverage of the NESWTDC
The estimated proportion of elective surgical separations covered by the NESWTDC data is calculated as the number of admissions for elective surgery reported to the NESWTDC, divided by the number of elective surgical separations (separations with an Elective urgency of admission and a Surgical Australian Refined Diagnosis Related Group for public hospital) reported to the NHMD, as a percentage.
For 2017–18, as the corresponding admitted patient care data were not available, this estimate was based on a comparison of the numbers of admissions and hospitals that were reported to the NESWTDC for 2016–17 and 2017–18, and the number of elective surgical separations reported to the NHMD for 2016–17.
- if the same hospitals were reported by a jurisdiction for the NESWTDC for both 2016–17 and 2017–18, the jurisdiction’s coverage was assumed to be the same for both years
- if the hospitals reported by a jurisdiction changed between 2016–17 and 2017–18, the jurisdiction’s coverage was adjusted by increasing (or decreasing) the numerator counts (NESWTDC admissions for 2016–17), based on the number of elective surgical separations reported for the individual hospital(s) to the NHMD for 2016–17
- if a hospital that was included in the NESWTDC for the first time in 2017–18 was not included in the NHMD for 2016–17, the number of elective surgical separations was assumed to be equal to the number of admissions from elective surgery waiting lists.
AIHW (Australian Institute of Health and Welfare) 2012. National health data dictionary version 16 2012. National health data dictionary series no. 16. Cat. no. HWI 119. Canberra: AIHW.
AIHW 2015a. National health data dictionary: version 16.1. National health data dictionary series no. 17. Cat. no. HWI 130. Canberra: AIHW. Viewed 27 March 2015,.
AIHW 2015b. National health data dictionary: version 16.2. National health data dictionary series no. 18. Cat. no. HWI 131. Canberra: AIHW. Viewed 27 March 2015.