New Zealand Cancer Registry - technical details

This section provides technical information on the data held by the Cancer Registry.

This section also includes information on what data is collected in the Cancer Registry and a table of available data.

Identity reporting

All records in NZCR have been linked to the NHI (National Health Index) and have a unique identifier (Health Care User number) assigned.

Ethnicity

Ethnicity information must be collected and classified according to the Ministry of Health's Ethnicity Data Protocols for the health and disability sector. In 2009 the way ethnicity was assigned in the NZCR changed with the introduction of an ethnicity algorithm. This algorithm was run retrospectively across all registrations back to 1989. With this method all records are assigned up to three ethnicity codes. This algorithm searches the NHI, the Mortality Collection and NMDS for ethnicity information.

The algorithm applies a 20% threshold for ethnicity data collected in NMDS (that is the ethnicity must be on 20% of records to be used in the algorithm). Events prior to 1989 retain their original ethnicity due to the lack of supplementary information from other data collections.

Geographical coding

The following geographical codes are assigned to cancer registrations:

  • Domicile code - Statistics New Zealand domicile code representing the healthcare user's usual residential address at the time of diagnosis. For domicile codes see the domicile code table.
  • Country of birth - sourced from hospital discharge events (from NMDS) or mortality events (from the Mortality collection).  See the country of birth code table on the Ministry of Health's website.
  • Health facility code - code of the health facility where the cancer was diagnosed or treated. See the facility code table on the Ministry of Health's website.

Coding systems

Two coding systems are used by the Cancer Registry:

  1. The WHO International Statistical Classification of Diseases and Related Health Problems (ICD) codes are used  to classify the tumour site (location).
  2. The WHO International Classification of Diseases for Oncology (ICD-O) is used to classify the tumour morphology (histology type and behaviour code).

Coding changes

ICD coding changes

Table 1: ICD (site) version changes
Year   Coding system
-1967 Mapped to ICD-9-CMA-II ICD-7
1968-1979 ICD-8
1980-1999   ICD-9
2000-2002 All records from 1948 mapped to ICD-10-AM in 2001. Also an ICD-9-CMA-II code is automatically derived and stored with the record. ICD-10-AM-II
2003-2008 ICD-10-AM-III
2009+ ICD-10-AM-VI

The changes and increasing detail over time may make it harder to map forward (mapping older data to new codes). Mapping the ICD-10-AM data back to ICD-9 CMA-II is useful for looking at time series data.

Morphology coding changes (ICD-O)

The third edition of ICD-O contains a revised morphology section. New classifications have been introduced and new codes assigned to accommodate them. This has resulted in changes to the coding of cancers diagnosed since 1 January 2003. For some tumour types, particularly haematological malignancies and ovarian cancer, these changes may affect incidence reporting. For particular cancer sites, registrations from 1 January 2003 onwards are not comparable with registrations prior to this date (see below).

Table 2: ICD-O (morphology) version changes
Year Coding system
Prior to 1995 ICD-O 1st edition 
1995 -2002 ICD-O 2nd edition 
2003+

ICD-O 3rd edition


Table 3: Recent morphology coding changes
  ICD-O 2nd edition  ICD-O 3rd edition Result 
Ovarian tumours of borderline malignancy Considered malignant  Considered to be of uncertain behaviour in the third edition and have been excluded from incidence reporting since 2003 Resulted in a slight reduction in the number of cases of ovarian cancer since 2003 compared with previous years.
Polycythaemia vera, myelodysplastic syndromes and chronic myeloproliferative disorders Considered to be of uncertain behaviour Considered to be malignant The ICD-10 codes for these new malignancies are in the range D45–D47 and were included for the first time in the 2003 data. A diagnosis of leukaemia in a person already registered with one of the above malignancies may not be counted in incidence statistics because of the way the coding rules for multiple primary tumours are applied (see the next section).
Pilocytic astrocytomas Considered malignant  Considered to be of uncertain behaviour Excluded from incidence reporting since 2003.

 

Table 4: Other coding changes
  Prior to 1 January 2005 From 1 January 2005  Description
Superficial transitional cell carcinoma of the bladder Considered invasive No longer considered invasive  Coded as in-situ and therefore excluded from incidence reporting. This resulted in a decrease in the number of bladder cancer registrations compared with previous years

Field changes

Some fields may be added, deleted of modified over time. For a list of the fields and any field changes please see the table of available data.

Data limitations

Trend data

Long-term trend data is unavailable for some fields and some cancer types. This  may be due to increasing/decreasing field details and changes to the inclusion/exclusion criteria (eg leukaemia and bladder cancers).

Coverage

Since the passing of the Cancer Registry Act 1993 and Cancer Regulations 1994, data quality and coverage significantly improved.

Staging data

Due to data quality issues staging information is not considered reliable prior to 1997.

Data quality measures

Routine data assurance measures include:

  1. Ensuring completeness of data collection by:
    1. monitoring reporting from laboratories
    2. reconciling information from multiple sources (NMDS, Mortality Collection, screening programme and clinician-maintained databases)
    3. using NHI (National Health Index) for identification purposes.
  2. Ensuring accuracy and completeness of coding by:
    1. electronic data entry validation checks such as morphology/site checks
    2. periodic manual checks of coding accuracy
    3. extensive pre-publication data checks (manual and automated)
    4. engineering the NZCR IT system to deal with the complex rules for recording and reporting multiple primaries, ensuring that duplicate registrations do not occur.
  3. Ensuring consistency of coding by:
    1. having specialist coders
    2. having an in-house procedure manual
    3. the use of international standards.
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