Comparability, Completeness and Validity: the Norwegian Cancer Registry Data
07 Aug 2018

Decision makers are generally used to evaluating data according to its internal validity, as has been the case for RCTs, however by doing this, understanding for the specifics for a disease or intervention can be neglected. A narrower focus is held, as opposed to looking at the whole picture; like real-life. Diseases or interventions rarely if ever occur in isolated situations, with a perfect identical population with no co-morbidities or previous medical history. This is where external validity and high-quality RWE comes in. By firstly understanding that a different approach would need to be taken to fully comprehend the rich data source RWDs are, a multitude of questions can be answered, that would otherwise be unanswerable using RCTs alone.

RWE as a source for high-quality data has been discussed in the past solely by industry and in research, however it has proven difficult to engage it in the area of policy and decision making. This field claim that there is simply a question of quality, with the discussion mainly focussed on the limitations of the data. Yet, when analysing the available RWD sources, there is substantial evidence that it not only exists, but is of a high quality. Perhaps if we are able to ‘prove’ quality data and the findings that can be sourced from it, RWE can truly enter the stage of decision making.

Continuing our series on Norway, and it’s RWDs ready to be tapped, let’s look at its Cancer Registry, and whether it can be classed as a high-quality RWD source.  A modern cancer registry must rely on its ability to carry out cancer control activities and its quality control procedures in place, state two authors associated with the Norwegian Cancer Registry (CRN). In a two-part review of the Norwegian Cancer Registry, the authors firstly aimed to provide an overview of the practical aspects and techniques concerning data quality at the cancer registry. This was done by examining the factors influencing key aspects of the registry, namely, the comparability, validity and timeliness of cancer registry data. The comparability of cancer data can be established via a comprehensive review of the registration routines in place. Validity is reviewed by numerical indices of that allows for comparisons with other registries, or, within a registry, over time, or in relation to a specified subset of cases. There are no international guidelines for timeliness at present, although specific standards for the reporting of registry data have been set out by some organisations.

This second instalment of a two-part review, focussed on the principles and techniques available for estimating completeness, separating methods into semi-quantitative – which give an indication of the degree of completeness relative to other registries or over time, and more quantitative techniques – those that provide a numerical evaluation of the extent to which all eligible cases have been registered.

Another author associated with CRN conducted a review to assess the quality of the data collected, concerning both solid and non-solid tumours. Unfortunately, the data assessed in the article went up to 2005, however the article did provide evidence for the positive assessment of the quality of the data in the registry. It was found that the coding and classification system used by the CRN, predominantly follows international standards, with some additional subdivisions of morphology groupings performed by the registry. The overall completeness was estimated at 98.8% for the registration period of 2001–2005. The completeness of cancer registry data, which refers to the extent to which all of the incident cancers occurring in the population are included in the registry database, is an extremely important attribute of a cancer registry. A high degree of completeness in case-finding procedures will ensure cancer incidence rates and survival-related data are as close to their true value as possible. There was found to be a variable degree of under-reporting for haematological malignancies (C90–95) and tumours of the central nervous system (C70–72), in particular. The under-reporting was estimated at 2.2% overall, based on the number of cases received at the registry during the following year.

The authors concluded that the routines in place at the CRN yielded comparable data that can be considered soundly accurate, close-to-complete and timely, thereby justifying the registry’s policy of the reporting of annual incidence once year after the year of diagnosis.

There have been more recent studies that have assessed the quality and appropriateness of using CRN for more specific cancer related issues, such as one concerning vaginal lesions, which have also concluded positively to the use of such data.

These articles suggest that the Norwegian Cancer Registry can be classed as a source of high-quality RWD, ie. RWD with adequate scope and quality of data to enable the development of high-quality RWE. Thus, can and should be supported by decision makers for use in assessments.


Articles of Interest:

Bray F, Parkin DM. Evaluation of data quality in the cancer registry: principles and methods. Part I: comparability, validity and timeliness. Eur J Cancer. 2009 Mar;45(5):747–55.

Parkin DM, Bray F. Evaluation of data quality in the cancer registry: Principles and methods Part II. Completeness. European Journal of Cancer. 2009 Mar;45(5):756–64.

Larsen IK, Småstuen M, Johannesen TB, Langmark F, Parkin DM, Bray F, et al. Data quality at the Cancer Registry of Norway: an overview of comparability, completeness, validity and timeliness. Eur J Cancer. 2009 May;45(7):1218–31.

Enerly E, Bray F, Mellem C, Hansen BT, Kjølberg G, Dahl T, et al. Quality assessment of the registration of vulvar and vaginal premalignant lesions at the Cancer Registry of Norway. Acta Oncol. 2012 Jan;51(1):45–50.