Cancer and Leukaemia (Hansard, 18 March 1987)

§ Mr. Mark Robinson

In the 1974–78 quinquennial report of the Wales cancer registry it was noted that both Clwyd and Gwynedd had elevated rates of registrations for all cancers combined when compared with other areas in Wales. This result remained when allowance was made for the differing age and sex structures of the areas concerned. Initial work on the quinquennial report covering the years 1979 to 1983 indicated that this differential persisted. However, in view of the registry's concern about the validity of the cancer registrations of both Clwyd and Gwynedd a validation exercise was initiated. This work required the comparison of computer listed entries against individual case notes, which necessitated the prior consent of the consultant involved in each case. As a consequence, the exercise has taken some time to complete. The results are set out in the following table:

differential, which remains even when allowance is made for the extent to which the age and sex structure of the 517W population of the area differs from that of Wales as a whole. There are no grounds at this stage for assuming any particular environmental factor is responsible.

Whereas the 1974 to 1978 quinquennial report of the Wales cancer registry indicated a higher rate of cancers for Gwynedd than for Clwyd, the present studies mostly indicate higher rates for the Clwyd portion of the north Wales coast than for the Gwynedd portion.

I have invited Professor Hubert Campbell, Emeritus Professor of Medical Statistics at the University of Wales College of Medicine, to undertake some further investigation of this data under the auspices of the steering committee for the proposed small area statistics unit announced today by my hon. Friend the Minister for Health.

Notes:

1. The North Wales Coast area is defined as comprising the areas of the following pre 1974 local authorities:

Clwyd

Connahs Quay
Flint MB
Holywell UD
Holywell RD
Prestatyn UD
Rhyl UD
Abergele UD
Colwyn Bay MB

Gwynedd

Llandudno UD
Conway MB
Penmaenmawr UD
Llanfairfechan UD
Ogwen RD
Bangor MB
Gwyrfai RD
Caernarfon MB
Lleyn RD
Beaumaris MB
Menai Bridge UD
Amlwch UD
Holyhead UD
Twrcelyn RD
Valley RD
Aethwy RD

2. The incidence of cancer varies greatly with age. The standardised registration rate (SRR) is an index which enables ready comparison of incidence rates in populations in different age and sex structures. The set of age-sex — specific incidence rates for Wales as a whole is denoted as the standard. These "standard" rates are then applied to the age-sex distribution of a particular area to calculate the number of registrations that would have been "expected" in this population had the area experienced, at each age, the cancer o incidence of the standard population. The "expected" incidence so found is then compared with the "observed" incidence and the ratio is multiplied by 100 to give an index in which 100 is the norm.

SRR = Observed incidence x 100/Expected incidence

3. The apparent overall increase in the rates recorded in the later quinquennium compared with the earlier may well be attributable to more efficient reporting of cases and does not necessarily indicate any true increase in the incidence of leukaemias and other malignancies.