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Quality of data (cancer rates)
One of the potential problems that may be present in trying to use data about
cancer incidence and mortality is the quality of the data. Those who use the
data in the manner of Gould and Sternglass are just going on faith that the
data are suitable for their purposes. I found the following information on
the Internet about an apparent huge difference in cancer incidence in Wales
as compared to England. It was resolved as being due to errors in reporting
the cases.
Note that near the end there is a caution about data quality. It is hard to
believe that there will not be differences in reporting techniques,
especially over long periods of time. Of course there are many other
potential problems that can affect reporting of this type, such as migration,
changes in the age of the population etc. The figures (graphs) mentioned are
not included here. It appears that data such as these are produced for local
reasons that have nothing do do with trying to find the cause of cancer and
that the quality of the data is not high enough for those purposes. I
suspect that is also the case with the data used by Gould and Sternglass.
___________________________________________________________
BONE CANCERS IN WALES: AN INVESTIGATION OF
CASES REGISTERED BY THE WALES CANCER
REGISTRY
Dr M C Cotter, Mr R T Kilpatrick, Mr G P Davies
Summary
On the basis of information produced by the Wales Cancer Registry
(WCR) concern has been expressed that the incidence of bone cancer
in Wales has been growing. According to WCR data, in 1989 the
crude rate of registration of the disease was 5 times that of
England.
The epidemiology of cancer would suggest that it is unlikely that such
rapid and pronounced changes are reflections of changes in the
incidence of the disease and may rather highlight a problem with the
data themselves.
In order to establish the true level of bone cancer among Welsh
residents an exercise to validate the data was undertaken. The
exercise
was initiated in 1993 and included a detailed assessment of each case
of bone cancer held by the WCR which was completed in 1995.
Registering cancers is a dynamic process in which the original data
may
be supplemented and revised by additional information for some time
after the cancer was first registered.
Figure 1 shows the differences between data for Wales published in
Annual Reference Volumes (ARV) by the National Cancer
Registration Scheme run by the Office of Population Censuses and
Surveys (OPCS) [Office for National Statistics (ONS) from April
1996] and data published by the WCR, both before and after the
validation exercise.
There were differences between the National Cancer Registrations
Scheme and the WCR publications which became more pronounced in
the late 1980s. However, both databases contained wrongly registered
bone cancer cases.
The numbers of cases in the revised data - where the erroneous cases
have been removed - are about a third of the number previously
registered overall and less than a fifth of the number originally
published
for 1989.
end page 1
Figure 1: Comparison of the number of cancer registrations
Figure 2 shows trends in the crude rate of registration of bone cancer
per 100,000 population for residents of Wales, comparing data
published by the National Cancer Registration Scheme with the revised
data.
The bone cancer registration rate published by OPCS was generally
higher than the WCR figure and in the late 1980s rose rapidly to
almost
5 cases per 100,000 population. This compared with a fairly constant
rate of less than 1 per 100,000 for England. After revision, the
annual
registration rate for Wales was also usually below 1 case per 100,000
population throughout the period 1979 to 1989.
Figure 2: Comparison of cancer registration rates
The study has confirmed the concerns of the WCR that the number of
cases of bone cancer on the register was overstated. The revised data
suggest that the incidence of the disease is, per head of population,
about the same as in England.
end page 2
The most significant factors that contributed to the over
registration of
bone cancer were (i) the miscoding of diagnoses from clinical notes,
in
particular those where soft tissue tumours of the head and neck were
mistakenly classified as bone cancers; and (ii) secondary cancers
being
recorded as primary cancers. There was no significant problem with
duplicate registrations. In a small proportion of registered cases
there
was no evidence of any reported cancer in the medical records.
These findings do not imply that there was any mis-diagnosis of cases
or that inappropriate treatment was given.
The exercise emphasises the importance of those involved in cancer
registration and the routine production of data for local
administrative
purposes producing accurate and timely information. Early validation
of
records is essential in order to resolve inconsistencies in the data
at an
early stage and while patient records are readily available.
There are lessons also for those who use the data. Cancer registration
is a complex process and those who use the information must be aware
of this. The data can only be best estimates of incidence at a
particular
point in time and those analysing the information should take account
of
data quality.
Acknowledgements
The authors would like to thank all those hospitals and staff who
participated in the validation exercise. Without this assistance,
often
provided in the face of other local clinical and administrative
demands, it would not have been possible to examine these cases of
bone cancer and establish the extent of the disease in Wales. Also,
the authors would like to thank Dr Neil Burnett, consultant
oncologist at Velindre NHS Trust, for his contribution and advice
on the aetiology of bone cancer, Dr Gerald Draper and Dr Charles
Stiller of the Childhood Cancer Research Group, for their help in
the preparation of this report and all the staff of the Wales Cancer
Registry for their hard work throughout the exercise.
____________________________________________________
R. Holloway
holloway3@aol.com
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