ReviewEvaluation of data quality in the cancer registry: Principles and methods. Part I: Comparability, validity and timeliness
Introduction
The role of the population-based cancer registry has evolved beyond that of a provider of information on cancer incidence within a defined catchment area.1 Given sufficient resources, the modern registry is active in a number of areas of cancer control, including epidemiological research on the causes of cancer, the monitoring and evaluation of screening programmes, and the follow-up of cancer patients in relation to the quality of cancer care they receive.2, 3 The value of a cancer registry and its ability to carry out such activities rely heavily on the quality of the data, and the quality control procedures in place.4, 5 Registries with a wide portfolio of activities will tend to improve the quality of their routine statistics simply by utilising the collected data, as well as by activating interest amongst collaborators (clinicians and researchers) in the daily registration procedures.6
As Skeet7 writes in the standard text on registry methodology, ‘all registries should be able to quote some objective measure of (ascertainment) rather than relying on received wisdom and pious hope’. This advice is not always heeded, however, and we take the opportunity here to provide some guidance on the practical aspects and techniques for addressing data quality at the cancer registry. This two-part review serves as a condensed update of the International Agency for Research on Cancer (IARC) Technical Report on the subject ‘Comparability and Quality Control in Cancer Registration’ published in 1994.8 An accompanying paper in this issue applies some of the methods described to the Cancer Registry of Norway.9
The three dimensions of quality addressed in the earlier publication8 were comparability, completeness and validity of registry data. Here, we also consider an additional quality indicator – the timeliness of registry procedures.
Comparability of the statistics generated for different population groups (registries, geographical areas, etc.), and over time, is essential to their meaningful interpretation. A basic requirement is the standardisation of practices concerning classification and coding of new cases, and consistency in basic definitions of incidence, such as rules for the recording and reporting of multiple primary cancers occurring in the same individual.
Completeness is the extent to which all the incident cancers occurring in the population are included in the registry database. Incidence rates and survival proportions will be close to their true value if maximum completeness in case-finding procedures can be achieved.
Validity or accuracy refers to the proportion of cases in the registry with a given characteristic that truly have that attribute, and depends on the precision of source documents and the level of expertise in abstracting, coding and recoding.
Timeliness of reporting of cancer registry results is an aspect of registry quality that can be considered as a separate issue, although this clearly influences the extent to which data are complete and accurate. Access to recent data is perceived as a priority by users, but, since registries are constantly updating their database as reports are received, and some notifications arrive long after the case was diagnosed, statistics for the recent periods will be incomplete, and will need future updates. There is, therefore, some conflict between the requirement for timely data, and other aspects of data quality, particularly completeness.
In Part I of this review, we consider in more detail the factors influencing comparability, validity and timeliness of cancer registry data, and the present methods available for evaluating the latter two. Part II reviews the topic of completeness.40
Section snippets
Comparability
Comparability is the extent to which coding and classification procedures at a registry, together with the definitions of recording and reporting specific data items, adhere to agreed international guidelines. The comparability of cancer data is thus identified via a thorough review of the registration routines in place, including a specification of the standards and definitions that have been followed. Precise knowledge of current and historical registration practices and definitions are of
Validity (accuracy)
Validity is defined as the proportion of cases in a dataset with a given characteristic (e.g. site and age) which truly have the attribute. Parkin et al.8 describe four groups of methods that provide numerical indices of validity, at least on an interval scale, and hence permit comparisons with other registries, or, within a registry, over time, or with respect to specified subsets of cases (certain sites, from different sources, etc.). They are: reabstracting and recoding, diagnostic criteria
Timeliness
Rapid reporting of information on cancer cases is another priority for cancer registries. Speedy access to cancer information is of clear benefit to health providers and researchers, and early provision of data usually enhances the reputation of the registry. There is, however, a trade-off between timely data and the extent to which it is complete and accurate; the speed at which the registry is able to report depends on numerous factors, and some of which are within the registry’s control and
Conflict of interest statement
None declared.
Acknowledgements
This study was undertaken as part of the Cancer Control using Population-based Registries and Biobanks (CCPRB) project, funded by the EU Sixth Framework Programme (FP6-2002-LifeSciHealth Contract No. 503465).
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