Childhood leukaemia, brain tumours and retinoblastoma near the Menai Straits, North 2000-2003 A response to a recent Green Audit report: - “Nuclear pollution, childhood leukaemia, retinoblastoma and brain tumours in and wards near the Menai Straits, North Wales 2000-2003” by C Busby PhD

Ceri White MMath, John Steward PhD FFPHM, Rachel Wade BSc Welsh Cancer Intelligence and Surveillance Unit, Cardiff

Background This internet report makes a number of claims concerning high risks of certain childhood cancers in North Wales. Part 1 makes reference to previous work carried out by Green Audit on downloads of tabulated data received from the Wales Cancer Registry (WCR) in 1996 covering the period 1982-1990. In part 2 of this report, data collected by HTV researchers concerning current cases are introduced and analysed in parts 3 to 5. Findings from the Green Audit analysis of these data suggest high relative risks for cancer in children aged 0-4 years and 0-14 years, mainly for leukaemia and brain tumours and living within the coastal towns near the Menai Strait.

To investigate this, WCISU have used data from the WCR frozen file (as of 1996) to produce tables regarding 1982-1990 to compare with Green Audit. Data for the period 1996-2003 have been extracted from the current LIVE database held at WCISU to obtain the most current and accurate data as possible. We follow the basic format of the Green Audit report.

Childhood Leukaemia (ICD10 codes C91-C95) ages 0-4 years for the period 1982-1990 The Green Audit studied cancer in North Wales using the Wales Cancer Registry data covering the period 1974-1990 and supplied to them some time in 1996. Tables 1a and 1b compare childhood leukaemia, aged 0-4 years in North Wales with apparent high relative risk for the period 1982-1990. Table 1a is taken from the report by the Green Audit. Table 1b is calculated from the WCR frozen file held at WCISU. Population figures were taken from the 1971 census Area of Residence (AOR) to calculate relative risk by WCISU. The overall rate for 0-4 years in Wales (for the period 1982-1990) was used as an external standard to calculate expected figures for the AOR in question.

Table 1a – Green Audit analysis, childhood leukaemia, ages 0-4, 1982-1990 AOR Obs RR 71CC Colwyn Bay 3 5.6 74CA Bangor 3 11.2 74CE 2 8.1

Table 1b – WCISU analysis, childhood leukaemia, ages 0-4, 1982-1990 AOR Obs RR 95% Conf. Int. 71CC Colwyn Bay 3 1.70 (0.35, 4.97) 74CA Bangor 3 2.48 (0.51, 7.26) 74CE Caernarfon 2 2.32 (0.28, 8.37)

In contrast to the Green Audit tables figures calculated by WCISU show no significant results. The small number of observed cases led inevitably to sample fluctuation as indicated by the wide confidence intervals.

1 Childhood Leukaemia in Caernarfon and in wards near the Menai Strait, ages 0-4 years for the period 2000-2003. (ICD10 codes C91-C95)

Caernarfon Table 4 of the Green Audit report states the wards used in the analysis along with population figures and expected number of cases for childhood leukaemia, ages 0-4. WCISU agree with the population figures from the 2001 Census since the areas of these wards are the same as the 1991 wards. Note that population figures for 2003 are not released at present – figures for 2002 were used in calculating rates in Wales for 2003 to enable calculation of expected figures for Caernarfon and Menai wards.

For the Green Audit analysis, incidence figures for the period 2000-2003 for childhood leukaemia, ages 0-4 years are analysed using the annual rate in England and Wales for 1997, 0.000067 as the external standard. WCISU used the equivalent Wales rate for the period 2000-2003 to calculate the expected figures, as is our usual practice.

Table 2 below shows the Green Audit analysis (Table 4 in their report) and compares it to WCISU.

Table 2 - Expected number of cases of Leukaemia per year, ages 0-4 years, 2000- 2003.

Busby WCISU Wards Pop 0-4 Expected 0-4 Expected 0-4 Cadnant 157 0.01052 0.0116 Menai 94 0.0063 0.0070 Peblig 158 0.0106 0.0117 119 0.008 0.0088 Caernarfon all per year 0.0354 0.0391

The expected numbers calculated by WCISU are slightly higher than Green Audit. We are analysing 4 years of diagnosis, 2000-2003, hence a total expected number of cases of 0.1564 cases for this period. However Green Audit incorrectly calculates total cases expected for only 3 years rather than 4 years, but uses incidence figures for 4 years, thus producing an inflated and incorrect RR.

A relative risk of 28 is calculated by Green Audit whereas a relative risk of 12.8 (95% CI: 1.5-46.2) is calculated by WCISU and can be seen in table 4 along with other time periods. The result by WCISU is statistically significant but lower than that calculated by Green Audit. Note the large confidence interval, based on only 2 observed cases (the Green Audit result was based on 3 cases). Incidentally a RR of 6.4 (95% CI: 0.2-35.7) would have been obtained for just 1 case in this area! This indicates the sensitivity of such statistics to data accuracy.

Menai Wards Green Audit lists all wards considered to be within 10km of the coast or with coastal proximity (Table 5 in their report). Green Audit use 1991 wards in the analysis along with populations as of the 2001 Census if the ward is in the 2001 Census, else the 1991

2 population figure is used. However Green Audit do not take into account the area covered by a particular ward from the 1991 Census compared with the 2001 Census. These areas change from 1991 to 2001 wards and this yields a corresponding change in population which Green Audit did not account for.

Table 3 lists all wards proximal to the coast or within 10km of the coast along with population figures for persons aged 0-4 years and expected cases of leukaemia. If the area of the ward has changed between the 1991 Census and 2001 Census then the 1991 Census figure is used by WCISU, else the 2001 figure is used since incidence figures are based on wards as of the 1991 Census. This is judged by WCISU to be the most accurate population for the ward in question. If the area of a 1991 ward has ‘extended’ into the sea but the rest of the area is the same then the 2001 Census figure is used since this may well be caused by increased accuracy of digitising of the 2001 wards. e.g. Garth and Hirael.

Table 3 – Menai Wards and populations used in analysis, ages 0-4 years.

Ward 91 1991 ID(G)1991 ID(W) Pop 0-4 (G) Exp. Leuk (G) Pop 0-4 (W) Exp. Leuk (W)

Bethel SZFA SZFA 100 0.0067 159 0.012 Bontnewydd SZFB SZFB 63 0.0048 71 0.005 Cadnant SZFC SZFC 157 0.011 157 0.012 Deiniol SZFD SZFD 41 0.0027 41 0.003 SZFE SZFE 149 0.01 110 0.008 Dewi SZFF SZFF 101 0.0068 101 0.007 Garth SZFG SZFG 27 0.0018 27 0.002 Gerlan SZFH SZFH 181 0.012 132 0.010 Glyder SZFJ SZFJ 90 0.006 90 0.007 Hendre SZFK SZFK 93 0.006 93 0.007 Hirael SZFL SZFL 70 0.0047 70 0.005 Llandigai SZFP SZFP 176 0.0118 176 0.013 /Aber SZFQ SZFQ 77 0.0051 77 0.006 SZFR SZFS 145 0.0097 168 0.012 Llanwnda SZFS SZFT 123 0.008 123 0.009 Marchog SZFT SZFU 114 0.0076 231 0.017 Menai Bangor SZFU SZFW 42 0.0028 42 0.003 Menai Caernarfon SZFW SZFX 94 0.0063 94 0.007 Ogwen SZFX SZFY 147 0.0098 147 0.011 Peblig SZFY SZFZ 158 0.0106 158 0.012 Penisarwaun SZFZ SZGA 114 0.0076 79 0.006 Pentir SZGA SZGB 159 0.0106 159 0.012 Rachub SZGC SZGD 98 0.0066 80 0.006 Seiont SZGD SZGE 218 0.0146 218 0.016 Waunfawr SZGF SZGG 119 0.008 119 0.009 SZGG SZGH 127 0.0085 127 0.009 TCFC TCFC 78 0.0052 78 0.006 Cadnant TCFH TCFH 40 0.0027 40 0.003 TCFK TCFK 84 0.0056 84 0.006 Llanfair Pwll TCFU TCFU 152 0.01 194 0.014 Llanfihangel ym TCFX TCFX 121 0.008 121 0.009 TCFZ TCFZ 96 0.0064 96 0.007 Rhosyr TCGK TCGK 128 0.0086 128 0.009 Tysilio TCGN TCGN 134 0.0089 134 0.010 TOTAL 3824 0.256 3924 0.290

3

From table 3, (G) indicates analysis by Green Audit and (W) indicates analysis by WCISU. The ward ID used by Green Audit is incorrect for 13 of the wards – that is, the codes and names for the wards do not match. Figure 1 shows the area under consideration by ward name and by ward ID. It is clear that ward name is correct so 1991 IDs have been changed to match (bold). Figure 2 and Figure 3 show the correct ward name and ID as of the 1991 Census to be used for the Caernarfon wards and Menai wards. Note that the Caernarfon wards are included in the Menai wards.

Italic figures in table 3 by Green Audit denote population figures taken from the 1991 Census. Population figures in bold italic for table 3 by WCISU (Pop 0-4 (W)) represent the ward not being of the same area for both census years, hence the population figure from the 1991 Census has been used in these cases. The population figure of 63 is incorrect for Bontnewydd and should be 71 from the 2001 Census – this has been changed in analysis by WCISU since both areas for both Censuses are of the same size. Llandigai (1991 ID SZFP), Llanllechid/Aber (1991 ID SZFQ), Rachub (1991 ID SZGD) and Llanfair Pwll (1991 ID TCFU) are not contained in the 2001 Census so the population figures for 1991 are used in the analysis by WCISU. The total figure by Green Audit should be 3816 and not 3824; this is an addition error by Green Audit. The population figure for Rachub should be 80 taken from the 1991 Census since this area is not defined in the 2001 Census. Green Audit have quoted a population figure of 98 for this area which is incorrect.

Figure 1 – 1991 Wards within coastal proximity or 10km within the Menai Strait

The Menai Wards in Anglesey and Gwynedd (10km of the Menai Strait)

3 3

Wards included by 1991 ID if using Wards included if using wards by name codes according to Green Audit according to Green Audit

4 WCISU observed 5 cases in the Menai wards above, Green Audit observed 6 cases in this area for the period 2000-2003 aged between 0 and 4 years. WCISU calculated a relative risk of 4.3 (95% CI: 1.4-10.0) – again note the wide confidence interval based on 5 observed cases. Green Audit calculated a significant relative risk of 7.8. Excluding the Caernarfon cases and wards Green Audit calculated a relative risk of 4.5 based on 3 cases. WCISU also observed 3 cases excluding the Caernarfon wards with a relative risk of 2.9 (95% CI: 0.6-8.6) indicating a non-significant result for children aged 0-4 years.

Note that for the twenty two year period 1982-2003 there were just 3 cases of childhood leukaemia (aged 0-4 years) diagnosed in the Caernarfon wards and 11 cases diagnosed in the Menai wards. Please note that these cases were taken from the live (current) database at WCISU whereas the analysis by Green Audit was based on the 1996 frozen file (1 case of leukaemia has since been deleted following validation).

A summary of the current analysis for the Caernarfon wards and Menai wards is given in Table 4 for five four-year periods from 1984 to 2003 (1991 Census population figures used for analysis up to 1995, a mixture of 1991 and 2001 population figures used for analysis post 1995). The table also shows analysis for 0-14 year olds.

Table 4 – Analysis for childhood leukaemia 1984-2003 (ages 0-4 and 0-14 years) Ages 0-4 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1984-1987 0 0.1 0.0 (0.0,27.9) 1 0.9 1.1 (0.0, 6.0) 1988-1991 1 0.2 5.8 (0.1,32.2) 3 1.2 2.5 (0.5, 7.2) 1992-1995 0 0.2 0.0 (0.0,24.2) 2 1.1 1.9 (0.2, 6.7) 1996-1999 0 0.1 0.0 (0.0,27.9) 0 1.0 0.0 (0.0, 3.8) 2000-2003 2 0.2 12.8 (1.5,46.2) 5 1.2 4.3 (1.4,10.0)

Ages 0-14 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1984-1987 0 0.2 0.0 (0.0,15.4) 4 1.7 2.3 (0.6,5.9) 1988-1991 1 0.3 3.9 (0.1,21.6) 4 1.9 2.1 (0.6,5.5) 1992-1995 0 0.3 0.0 (0.0,13.8) 2 1.9 1.0 (0.1,3.7) 1996-1999 0 0.3 0.0 (0.0,12.9) 1 2.1 0.5 (0.0,2.7) 2000-2003 3 0.3 10.1 (2.1,29.6) 7 2.2 3.2 (1.3,6.7)

For the more usual age band 0-14 years, an increased risk of childhood leukaemia for the period 2000-2003 is still evident for the Caernarfon and Menai wards although the actual relative risks have decreased slightly.

Table 5 shows comparison of the two time periods, 1982-1999 and 2000-2003 which show no evidence of an increased risk of childhood leukaemia, 0-4 years or 0-14 years for the eighteen-year period 1982-1999.

5 Table 5 – Analysis for childhood leukaemia 1982-2003 (ages 0-4 and 0-14 years)

Ages 0-4 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1982-1999 1 0.7 1.5 (0.0, 8.2) 6 4.8 1.3 (0.5, 2.7) 2000-2003 2 0.2 12.8 (1.6, 46.2) 5 1.2 4.3 (1.4, 10.0)

Ages 0-14 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1982-1999 1 1.2 0.9 (0.0, 4.8) 12 8.4 1.4 (0.7, 2.5) 2000-2003 3 0.3 10.1 (2.1, 29.6) 7 2.2 3.2 (1.3, 6.7)

Table 6 groups the eighteen-year period 1982-1999 into two nine-year periods. The nine year period 1982-1990 shows a significant increased risk of childhood leukaemia for the Menai wards, ages 0-14 years. However the following nine-year period does not show an increased risk of childhood leukaemia in the Menai wards.

Table 6 – Split period analysis for childhood leukaemia 1982-2003 (ages 0-4 and 0- 14 years)

Ages 0-4 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1982-1990 1 0.3 2.9 (0.1, 16.3) 4 2.4 1.7 (0.5, 4.3) 1991-1999 0 0.3 0.0 (0.0, 10.9) 2 2.4 0.8 (0.1, 3.0) 2000-2003 2 0.2 12.8 (1.5, 46.2) 5 1.2 4.3 (1.4, 10.0)

Ages 0-14 Caernarfon Wards Menai Wards Obs Exp RR 95% CI Obs Exp RR 95% CI 1982-1990 1 0.5 1.9 (0.0, 10.3) 9 3.9 2.3 (1.1, 4.4) 1991-1999 0 0.6 0.0 (0.0, 5.9) 3 4.5 0.7 (0.1, 2.0) 2000-2003 3 0.3 10.1 (2.1, 29.6) 7 2.2 3.2 (1.3, 6.7)

6 Figure 2 – Identification of the 1991 “Caernarfon Wards”

Caernarfon Wards (1991 Census)

Code 1991 ID 1991 Ward Name 1 SZFX Menai Caernarfon 1 2 SZFC Cadnant 2 3 SZFZ Peblig 3 4 SZGG Waunfawr

4

Figure 3 – Identification of the 1991 “Menai Wards”

Menai Wards (1991 Census) – 10km of the Menai Strait

Code 1991 ID 1991 Ward Name 27 1 SZFA Bethel 2SZFBBontnewydd 29 3 SZFC Cadnant 4 SZFD Deiniol 34 5 SZFE Deiniolen 31 7 11 30 17 6SZFFDewi 28 4 16 9 10 7SZFGGarth 6 13 8 SZFH Gerlan 9 SZFJ Glyder 32 22 10 SZFK Hendre 23 11 SZFL Hirael 19 26 1 12 SZFP Llandigai 33 8 13 SZFQ Llanllechid/Aber 12 21 14 SZFS Llanrug 18 15 SZFT Llanwnda 3 16 SZFU Marchog 20 14 17 SZFW Menai Bangor 24 5 18 SZFX Menai Caernarfon 2 19 SZFY Ogwen 20 SZFZ Peblig

15 25 21 SZGA Penisarwaun 22 SZGB Pentir 23 SZGD Rachub 24 SZGE Seiont 25 SZGG Waunfawr 26 SZGH Y Felinheli 27 TCFC Beaumaris 28 TCFH Cadnant 29 TCFK Cwm Cadnant 30 TCFU Llanfair Pwll 31 TCFX Llanfihangel Ysgeifiog 32 TCFZ Llanidan 33 TCGK Rhosyr 34 TCGN Tysilio

7 Table 7 shows the relative risks and 95% confidence intervals for childhood leukaemia in Anglesey and Gwynedd, ages 0-4 and 0-14. Note that observed figures in Anglesey and Gwynedd are very small and hence confidence intervals are wide. No significant results are obtained.

Table 7 – Relative risks in Anglesey and Gwynedd 1984-2003 for childhood leukaemia (ages 0-4 and 0-14 years)

0-4 Anglesey Gwynedd Obs Exp RR 95% CI Obs Exp RR 95% CI 1984-1987 0 1.0 0.0 (0.0, 3.8) 1 1.4 0.7 (0.0, 4.0) 1988-1991 2 1.3 1.5 (0.2, 5.6) 3 1.3 1.5 (0.3, 4.4) 1992-1995 0 1.1 0.0 (0.0, 3.4) 2 1.8 1.1 (0.1, 4.0) 1996-1999 2 1.0 2.0 (0.2, 7.2) 0 1.7 0.0 (0.0, 2.1) 2000-2003 3 1.0 2.9 (0.6, 8.4) 3 2.0 1.5 (0.3, 4.5)

0-14 Anglesey Gwynedd Obs Exp RR 95% CI Obs Exp RR 95% CI 1984-1987 2 2.1 1.0 (0.1, 3.5) 3 2.9 1.0 (0.2, 3.0) 1988-1991 2 2.1 0.9 (0.1, 3.4) 5 3.2 1.6 (0.5, 3.7) 1992-1995 1 2.2 0.5 (0.0, 2.6) 2 3.4 0.6 (0.1, 2.1) 1996-1999 4 2.2 1.8 (0.5, 4.7) 3 3.7 0.8 (0.2, 2.4) 2000-2003 3 2.1 1.4 (0.3, 4.1) 5 3.7 1.3 (0.4, 3.1)

8 Brain and spinal tumours in children 0-14 years in the Menai area 1996- 2003 (See Appendix 1 for ICD10 codes)

It is not clear from their report whether Green Audit have analysed tumours (both malignant and benign) which is the usual practice or just malignant tumours, hence this section deals with both contingencies (we denote these as MB and M respectively).

Caernarfon Green Audit use the 1991 Census population to calculate expected figures for brain and spinal tumours for the period 1996-2003. It is unclear why 1991 population figures have been used since 2001 population figures were used for childhood leukaemia for the same area and were more appropriate for this analysis.

Table 8 shows the difference between the 1991 and 2001 Census populations for the Caernarfon wards. The wards were of the same size for both Censuses.

Table 8 – Comparison of population figures as of the 1991 and 2001 Census, ages 0-14 years.

1991 Census (Green Audit) 2001 Census (WCISU) 0-4 5-9 10-14 0-14 0-4 5-9 10-14 0-14 Waunfawr 110 104 95 309 119 100 100 319 Cadnant 93 100 114 307 157 159 124 440 Menai C 128 128 111 367 94 108 131 333 Peblig 277 236 159 672 158 191 228 577 All wards 608 568 479 1655 528 558 583 1669

Green Audit state that for the eight-year period 1996-2003 there were 5 observed cases, 0.28 expected cases representing a relative risk of 17.8.

WCISU calculated expected figures based on the 0-4, 5-9 and 10-14 year old populations for the 1996-2003 rate in Wales. Table 9 shows that there was just 1 case observed for the Caernarfon wards stated above, hence a relative risk of 1.8 (95% CI: 0- 10.2) for all brain and spinal tumours (MB). There were no observed cases for all brain and spinal malignancies (M), hence in contrast WCISU would calculate a relative risk of 0 (95% CI: 0-8.5).

Table 9 – Analysis of brain and spinal tumours in Caernarfon wards, ages 0-14 years for the period 1996-2003.

Obs Exp RR 95% CI Green Audit 5 0.3 17.8 CI N/A, p<0.00001 WCISU (MB) 1 0.5 1.8 (0.0, 10.3) WCISU (M) 0 0.4 0.0 (0.0, 8.5)

9 Menai Wards

Green Audit calculate relative risks for brain and spinal tumours in 0-15 year olds for the Menai area. They state that 1 person was identified in this area aged 15 yet all other analyses only go up to age 14. The analysis by WCISU uses ages 0-14 since there is no single year of age population available by ward. As in previous analysis, the population figures for the Menai wards were of the 2001 Census unless the areas of the 1991 wards were not the same compared with the 2001 wards or the 1991 ward was not available in the 2001 Census.

Table 10 shows the comparison between the analysis conducted by Green Audit and WCISU. (MB) denotes malignant and benign, (M) denotes malignant.

Table 10 – Analysis of brain and spinal tumours in the Menai wards, ages 0-14 years for the periods 1996-2003 and 1999-2003.

GREEN AUDIT WCISU Observed Expected RR Observed Expected RR 95% CI 1996-2003 92.14.31996-2003 (MB) 4 3.9 1.0 (0.3,2.6) 1999-2003 71.35.41999-2003 (MB) 3 2.3 1.3 (0.3,3.8) 1996-2003 92.14.31996-2003 (M) 2 3.1 0.6 (0.1,2.3) 1999-2003 71.35.41999-2003 (M) 2 1.9 1.0 (0.1,3.7)

In contrast to Green Audit (their Table 8 refers), the analysis by WCISU shows no significant results in the Menai area either for malignant and benign tumours (MB) or for malignant brain and spinal tumours (M).

10 Retinoblastoma (ICD10 code C692), ages 0-14 years for the period 1994- 2003

Green Audit state that there were six cases of retinoblastoma in the data- 2 in Conwy and 1 in Caernarfon. They also state that there were 3 cases, all teenagers diagnosed in Anglesey. Later they state that six cases give a relative risk of 4.8 in Gwynedd. It is unclear whether they are referring to the same six cases. Green Audit quote population figures that were used in the analysis for Anglesey and Gwynedd (0-14 years) of 11,129 and 33,797 respectively. However figures from ONS quote population figures for Anglesey and Gwynedd of 12,368 and 21,236 as of the 2001 Census.

The analysis by WCISU show 21 cases of retinoblastoma in Wales (note 7 of these cases were for the year 2003) for the ten-year period 1994-2003 for ages 0-14. (Note there were no cases in Wales for the age band 15-19). Table 11 shows incidence of retinoblastoma for the period 1994-2003 in Wales, Anglesey, Gwynedd and Conwy.

Table 11 – Incidence of Retinoblastoma in Wales and North West Wales, ages 0-14 years for the period 1994-2003.

Wales Anglesey Gwynedd Conwy 1994 1000 1995 0000 1996 3001 1997 2000 1998 3000 1999 2000 2000 0000 2001 1000 2002 2000 2003 7011 TOTAL 21 0 1 2

Green Audit state that 3 cases were diagnosed in Anglesey but WCISU report no cases in Anglesey for the ten-year period 1994-2003. Table 12 shows relative risks calculated by WCISU for Anglesey, Gwynedd and Conwy using the rate of retinoblastoma in Wales to calculate expected figures (Wales 0-14 year rate = 0.38 per 100,000 population). No results were significant. Again note the small number of cases involved over the ten- year period and an increase or decrease of just one case will greatly affect the relative risk.

Table 12 – Analysis by local health board in North West Wales, ages 0-14 years for the period 1994-2003.

Anglesey Gwynedd Conwy Observed 012 Expected 0.48 0.81 0.71 RR 0.00 1.24 2.82 95% CI (0.0,7.7) (0.0,6.9) (0.3,10.2)

11 Discussion

The report was produced by a campaign group who have claimed on a number of previous occasions to have uncovered evidence that low level radioactive discharges from nuclear facilities such as Sellafield have led to increased levels of cancers in Wales and elsewhere in the UK. However investigations by WCISU and others have revealed gross data errors and methodological flaws in these reports which consequently have little scientific value.

In respect of the analysis 1982-1990, this was based on an extract from WCR taken in 1996 and WCISU have been able to check this against the state of the database at that time. Table 1a (Table 1 in Green Audit report refers) has the correct observed data but an incorrect analysis and interpretation has inflated the risks to the extent which they appear alarming to the public. Table 1b provides the correct analysis which is well within the realm of chance variation. Table 1b, which unlike Table 1a uses 95% confidence intervals, shows the wide range of uncertainty which results from using such small numbers.

The second analyses are based on data provided for Green Audit by HTV. A reporter was investigating cancer services for North Wales children at Alder Hey and carried out some sort of “snowball” survey. The details would presumably be based on anecdotal reports from parents and relatives. Other studies have shown that self reported diagnoses are frequently inaccurate. The population at risk is also unclear.

WCISU data is collected from hospitals and relevant cancer registries outside Wales. WCISU data is complete up to the end of 2002 but 2003 is still coming in. However with help from clinical colleagues, our peripatetic data validation officers have attempted to locate all childhood cases in Wales up to the end of 2003. We are grateful to the Mersey and Cheshire Cancer Registry for assisting us by expediting an inter-regional data transfer of validated cases from Alder Hey.

Green Audit have made some fundamental errors. Firstly they underestimate the expected numbers for Caernarfon Wards by multiplying by 3 years instead of 4. There is also some confusion in the geographical analysis using 1991 wards and 2001 population. WCISU have tried to reproduce the intended analysis with the correct population data. WCISU have reproduced an error of this type in a previous analysis by Green Audit where a spurious cancer cluster was produced1

In respect of the Caernarfon wards, WCISU confirm that the relative risk for childhood leukaemia 0-4 for the period 2000-2003 is significantly raised RR= 12.8 (95% CI: 1.5, 46.2). However this is based upon only two cases. A RR of 4.3 (95% CI: 1.4, 10.0) was calculated by WCISU for childhood leukaemia in the Menai wards based on 5 cases. Again we note a wide confidence interval. All we can say is that based on the assumption of a Poisson distribution, we reject the null hypothesis that the RR is 1.0. There is a wide range to the confidence intervals illustrating the high level of uncertainty consequent on such small numbers. Green Audit favour the use of p-values in their reports which have a more dramatic impact but in our considered view they can be totally misleading in this context. One of the factors described by Gardner that may lead to inflated p values arise from the fact that observed counts are discrete integers (whole numbers) and these are divided by expected counts expressed as real numbers (decimal fractions), consequent on applying a rate to the population count, and this can

12 give a spurious asymptotic effect2. The other inherent pitfalls in the interpretation of small cancer counts including the inappropriate application of statistical methods have all been detailed by WCISU in the context of a commentary on the Green Audit’s report on Childhood Cancer near Chepstow3.

As regards the Green Audit claims for brain and spinal tumours 0-15yrs in the Menai area, WCISU could find no evidence in their analysis 0-14yrs for a significantly raised RR (see Table 10). Similarly for retinoblastoma, WCISU could find no evidence for raised RR (see Table 12).

Thus most of the claims for raised RR in the Green Audit report could not be supported by analysis of the cancer registry database for Wales held by WCISU. The one result confirmed of raised RR for childhood leukaemia in Menai wards 2000-2003 depends on five cases. That is only weak evidence for the postulated effect. Lack of any effect prior to 2000 suggests that this is a statistical blip - possible selected a priori before testing its significance. Moreover, BNFL Sellafield has been in operation long before 2000 and evidence for any consistent increase in risk over time is lacking.

Previous analysis by WCISU4 has failed to reveal any coastal effect on childhood cancer rates in Wales despite claims by Green Audit to have demonstrated such an effect. We were also unable to confirm the claimed raised risk of breast and prostate cancer near Cheptow3. The raised incidence of leukaemia in that area of Wales was confirmed3 but was dependent on a very small number of cases. Conventional guidelines6 for investigation of cancer clusters caution against over-interpretation of statistical findings in such situations.

Why the discrepancy between the data analysed by Green Audit and that held by WCISU? Some critics might argue that the informal survey by HTV provided more accurate and complete figures than those resulting from the cancer registration process. It is true that inherent delays in the registration process make it difficult to report complete figures with confidence within twelve months of the incidence year and owing to the dynamic nature of registration it may take as much as five years for rates to stabilise. However once collected, using multiple sources, these data are subject to ongoing rigorous 100% validation by checking with clinicians. We also undergo annual peer review QA with other registries within the UK via the UKACR. In fact at our most recent review in 2004, childhood cancer data for Wales was judged to be high quality.

On the other hand, the collection of anecdotal medical reports by lay persons is a notoriously error-prone process. For example there are obvious internal inconsistencies in the dates given in Green Audit’s table 2. Moreover some of the addresses appear to be from outside the study area. Owing to the enormous amount of additional work carried out by WCISU to validate and collate these childhood cases up to the end of 2003 and the valued assistance of clinicians who treat them we think that incompleteness of data is a very unlikely explanation for the gross discrepancy with Green Audit’s findings. We are also very grateful to the Director of the CCRG Oxford for an up to date download of Welsh data held up to the end of 2003 and very useful comments. Checking against this “gold standard” childhood cancer database did not change our results. We conclude that the Green Audit report is in error.

13 Green Audit have a well reported track record of producing flawed and alarmist reports for the media (see COMARE website for details5). This appears to us to be yet another example. However under our surveillance remit with the Welsh Assembly Government, WCISU will continue to monitor the Menai wards as well as the rest of Wales for childhood cancer incidence.

14 References

1.Roberts RJ, Steward JA, John G.(2003) Cement, cancers and clusters: an investigation of a claim of a local excess cancer risk related to a cement works. J. Public Health Medicine 25(4):351-357.

2. Gardner MJ (1989) Review of increases in childhood cancer rates in the vicinity of nuclear installations in UK. J.R.Statist. Soc. A;152;307-325 [fig 2 p313 refers]

3 Steward JA, Wright M, White C (2002) Part 1:Childhood cancer incidence in the Chepstow area 1974-1998. Part II: Female breast cancer and male prostate cancer in the Chepstow area 1985-1998. A report to the Welsh Assembly Chief Medical Officer. (available from http://www.wales.nhs.uk/sites/page.cfm?orgid=242&pid=1738)

4. Steward JA, John G (2001). An ecological investigation of the incidence of cancer in Welsh children for the period 1985-1994 in relation to residence near the coastline. J.R. Statist. Soc. A ;164:29-44.

5.COMARE statement: Childhood Leukaemia in Wales (available from http://www.comare.org.uk/statements/comare_statement_wales.htm)

6. Leukaemia Research Fund. Handbook and Guide to the Investigation of Clusters of Disease. LRF Centre for Clinical Epidemiology, University of Leeds, Summer 1997 [pages 104-105 refer].

Appendix 1

ICD10 codes used by WCISU for brain and spinal tumours:

Malignant C70, C71, C72, C793

Benign D320, D321, D329, D343, D429, D432, D330, D331, D332, D333, D337, D339, D352, D353, D354, D421, D430, D431, D437, D439, D420, D433, D434, D443, D444, D445

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