Information for Researchers
Types of Linkage Services
The CHeReL offers three types of record linkage services:
- Extracts from the Master Linkage Key
- Linkage of other datasets with the Master Linkage Key
- Linkage of datasets not included in the Master Linkage Key, including internal linkage or de-duplication of a dataset
The Master Linkage Key consists of ‘pointers’ to records for specific people in health-related databases. The databases that are currently approved to have records in the Master Linkage Key are:
- NSW Admitted Patient Data Collection
- NSW Emergency Department Data Collection
- NSW Midwives Data Collection
- NSW Perinatal Death Review Database
- NSW Central Cancer Registry
- NSW Pap Test Register
- NSW Registry of Births, Deaths and Marriages birth registration data
- NSW Registry of Births, Death and Marriages death registration data
- ABS Mortality Data
- ABS Perinatal Mortality Data
- The 45 and Up Study
A single source of metadata for many of these collections is available; please contact us to obtain access.
NSW Admitted Patient Data Collection
The Admitted Patient Data Collection covers all inpatient separations (discharges, transfers and deaths) from all Public (including Psychiatric), Private, and Repatriation Hospitals, Private Day Procedures Centres and Public Nursing Homes in NSW. Patient separations from Developmental Disability Institutions and Private Nursing Homes are not included. The collection also includes data relating to NSW residents hospitalised interstate (see below for more details) and in Commonwealth Department of Veteran’s Affairs facilities. However, as interstate data contain insufficient information to be included in record linkage studies.
The APDC is a financial year collection from 1 July through to 30 June of the following year. Prior to 1993/94 the APDC was a sample of all inpatient separations. In 1993/94 the Admitted Patient Data Collection became fully enumerated. Hospitals are required to submit details for every inpatient and for every episode of care. A separate return is processed for each period of inpatient care, irrespective of the time interval between the date of separation and subsequent re-admission.
Until 30 June 1998 the APDC is available as periods of stay in hospital. A period of stay in hospital ended with a discharge, transfer or death of a patient. If a patient was admitted to hospital five times in a year, at least five separate records were included in the Admitted Patient Data Collection (the actual number of records generated depended on the occurrence of “statistical separations”). In psychiatric hospitals and psychiatric units of public hospitals, patients who were on leave for a period of greater than 10 days were recorded as statistical separations. Patients of other hospitals who were on leave for a period greater than 4 days were also recorded as statistical separations.
APDC data for the years 1998/99 onwards are available as Episode of Care (EOC). An episode of care ends by either the patient ending a period of stay in hospital (i.e. by discharge, transfer or death) or by the patient becoming a different type of patient within the same period of stay in hospital. The categories of types of care are found in the variable "Service Category".
Record Linkage
The Master Linkage Key currently contains records from 1 July 2000 onwards.
For record linkage studies involving APDC data prior to 1 July 2000, there is a risk of losing true links due to limited information available for matching. For events that are close in time, say a few weeks apart, linkage with APDC records can be considered reliable. Caution must be exercised in considering the impact of lost links for events that likely to be more than 3 months apart. The magnitude of the problem of missed links over time is difficult to assess. The NSW Department of Health has estimated that even when hospital code and medical record number are included to capture readmissions to the same hospital, roughly 10% of hospital readmissions are lost per year of follow-up. The risk is increased for events likely to be further apart.
NSW Emergency Department Data Collection
The Emergency Department Data Collection (EDDC) derives from the Emergency Department Information System. Data are available from 1 July 1996. The original purpose of the project was to capture waiting time data. Secondary aims have included the capture of better information about emergency departments to assist clinicians in the management of emergency department services.
Record Linkage
The Master Linkage Key will contain records from July 2000 onwards. For events that are close in time, say a few weeks apart, linkage with APDC records can be considered reliable. Due to limited information available for linkage, t here is a risk of losing true links over time. Caution must be exercised in considering the impact of lost links for events that likely to be more than 3 months apart . The magnitude of the problem of missed links over time is difficult to assess. The NSW Department of Health has estimated that even when hospital code and medical record number are used roughly 10% of links will be lost per year of follow-up. It may be possible to use other sources of information such as the Admitted Patient Data Collection to obtain additional information that could then be used for further record linkage.
NSW Midwives Data Collection
The MDC is a population-based surveillance system covering all births in NSW public and private hospitals, as well as homebirths. The data collection has operated since 1987 but only continuously since 1990. In 1992, the MDC became a statutory data collection under the NSW Public Health Act 1991.
The MDC encompasses all live births and stillbirths of at least 20 weeks gestation or at least 400 grams birth weight. The MDC relies on the attending midwife to complete a notification form when a birth occurs. The form includes demographic items and items on maternal health, the pregnancy, labour, delivery and perinatal outcomes and has undergone revisions in 1990, 1993, 1998 and 2006.
The MDC includes notifications of births which occur in NSW; it does not receive notifications of interstate births where the mother is resident in NSW.
Record Linkage
The Master Linkage Key will contain records from January 1994 onwards.
It is recommended that record linkage studies be carried on out data collected from 1994, due to limited information for linkage available in previous years.
NSW Central Cancer Registry
The Central Cancer Registry (CCR) receives notifications of cancer in NSW. It is managed by the Cancer Institute NSW for the NSW Health Department, and operates under the authority of the Public Health Act 1991. The Registry maintains a record of all cases of cancer diagnosed in NSW residents since 1972.
The CCR is a case-based register in which all notifications relating to a particular case of cancer are linked to form a single record. A case of cancer is the occurrence of a malignant neoplasm in one organ of a particular person. Therefore a case of malignant melanoma in a particular person counts as one case. If the same person subsequently develops leukaemia, the leukaemia counts as a second case.
More information on the CCR can be found on the web at: www.cancerinstitute.org.au/programs/centralcr.html.
Record Linkage
The Master Linkage Key will contain records from January 1994 onwards.
While deaths due to cancer that occur in hospital are reported to the CCR under the Public Health Act, deaths occurring elsewhere may not be reported. Under an agreement with the Registry of Births, Deaths and Marriages the CCR matches information on death registrations where the death is due to cancer. Access to linked CCR/death data is subject to ethics committee approval, but does not require separate approval of the Registrar of Births, Deaths and Marriages.
NSW Pap Test Register
The NSW Pap Test Register (PTR) is a central and confidential record of NSW women’s Pap Tests and related follow-up test results. The PTR was established in 1996 under the NSW Public Health Act 1991. It is a key part of the NSW Cervical Screening Program, which aims to reduce the incidence and mortality from cervical cancer by promoting regular screening. The Cervical Screening Program follows the NHMRC guidelines for the management of asymptomatic women with screen-detected abnormalities.
The Cancer Institute NSW manages the PTR on behalf of the NSW Department of Health. Further information on the PTR can be found on the Cancer Institute NSW website at: www.cancerinstitute.org.au/programs/ptr.html.
Record Linkage
The Master Linkage Key will contain records from January 1996 onwards.
While the results of all Pap tests in NSW are included on the PTR, record linkage studies can only be carried out using records of women who choose not to opt-off the Register. The rate of participation in the NSW Cervical Screening Program for women in the target age group 20 - 69 years is about 60%.
Further information on participation rates can be found in the annual statistical report of the NSW Cervical Screening Program. Reports for recent years are available on the Cervical Screening Program website.
NSW Registry of Births, Death and Marriages birth and death registration data, ABS Mortality data and ABS Perinatal Mortality Data
The NSW Registry of Births Deaths & Marriages records all births that occur in New South Wales.
All deaths for which a coronial inquiry is not required must be certified as to cause and date by a registered medical practitioner and the certificate registered by the RBDM in each State and Territory. Deaths that are referred to a Coroner are registered by the Coroner at the conclusion of an inquiry into the circumstances of the death. The vast majority of non-Coronial deaths are registered with the relevant RBDM within 4 weeks of the date of death. However, Coronial inquiries can take longer to conclude, often a number of months, and in some cases may take years to finalise.
State and Territory Registrars of Births, Deaths and Marriages and all Coroners forward details of all deaths that they have registered to the ABS. The ABS checks and codes the information. A single code for an underlying cause of death was applied up to 1997. Starting with 1997 registrations, multiple cause of death codes (ICD10) are applied to each death record if more than one cause contributed to the death.
Mortality data is supplied by ABS by year of registration. Therefore, deaths occurring in the last few weeks of each calendar year (or the last few months for coronial cases) may not be registered until the following year.
Record Linkage
The Master Linkage Key will contain records for 1994 onwards.
If researchers wish to obtain information on the date of death then access to Registry of Births, Deaths and Marriages (RBDM) death registration data should be included in any project proposal/ ethics application.
If researchers wish to obtain information on both the fact of death and cause of death, then access to both RBDM death registration data and ABS mortality data should be included in any project proposal/ ethics application.
In NSW death records that are available for linkage include deaths occurring in NSW and do not include deaths of NSW residents who die interstate. The Australian Institute of Health and Welfare (AIHW) holds the National Death Index, which can be used for research studies that require linkage of death records for persons who die interstate. Information on the National Death Index can be found on the AIHW website at http://www.aihw.gov.au/cancer/ndi/index.cfm