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Cancer in Scotland: Sustaining Change
Cancer Incidence Projections for Scotland (2001-2020)
An Aid to Planning Cancer Services
APPENDIX A: EMPIRICAL TESTING
To test the validity of the chosen models they were fitted using data from 1961-1990 and the projected numbers of cases were then estimated for 1991-2000 using the same projection method as used for the main analysis applied to the most parsimonious model. The differences between the observed and predicted values (
see Table A1) show that overall the estimate was very close (difference 1,588 cases; 1.2% higher than was actually observed), but for individual cancer sites the accuracy of the predictions did vary considerably.
The prediction underestimated the true number of cases by more than 20% for cancers of rectum in males, melanoma in females, prostate and brain in males. Male rectal cancers and prostate cancers saw a rise in the 1990s that could not have been predicted beforehand. The models performed poorly at predicting the trends for females with melanoma - a very conservative model (predicting 1,533 cases) being chosen over a highly escalating model (2,734 cases). A similar situation was observed for males with brain cancer. Due to this, the younger age groups were modelled differently in the main analyses.
The prediction overestimated the true number of cases by more than 20% for cancers of cervix, melanoma in males, NHL, leukaemia, and other and unspecified tumours in males. The decrease in cervical cancers was a result of service re-organisation that could not have been predicted beforehand. The rate of increase in melanoma in males in the 1980s did not continue in the 1990s and this also could not have been predicted. Trends in the other and unspecified tumours are difficult to comment on because they comprise of a mixed group of tumours. The models performed poorly at predicting the trends for NHL and leukaemia. Again, as a result of this, the younger age groups were modelled differently in the main analyses.
Table A1: Accuracy of the predicted compared to observed estimates for 1996-2000; prediction based on 1961-1990 trends and known population estimates
Cancer group | Sex | Observed Cases | Minimum Difference |
Model | N | % |
Head and Neck | M | 3,441 | D2 | 103 | 3.0% |
F | 1,492 | D1 | -178 | 11.9% |
Oesophagus | M | 2,315 | D1 | 155 | 6.7% |
F | 1,586 | D1 | 49 | 3.1% |
Stomach | M | 2,830 | D1 | 303 | 10.7% |
F | 1,974 | ND3 | -178 | 9.0% |
Colon | M | 5,605 | D2 | -360 | 6.4% |
F | 5,728 | D1 | 63 | 1.1% |
Rectum | M | 3,478 | D1 | -717 | 20.6% |
F | 2,417 | D3 | -20 | 0.8% |
Lung | M | 13,442 | D2 | 351 | 2.6% |
F | 9,878 | D2 | -118 | 1.2% |
Pancreas | M | 1,487 | D2 | 55 | 3.7% |
F | 1,666 | D3 | -220 | 13.2% |
Melanoma of skin | M | 1,367 | D2 | 399 | 29.2% |
F | 1,912 | ND1 | -379 | 19.8% |
Breast | F | 17,392 | D2 | 310 | 1.8% |
Cervix | F | 1,709 | D3 | 831 | 48.6% |
Corpus uteri | F | 2,194 | ND1 | -332 | 15.2% |
Ovary | F | 3,045 | D1 | 84 | 2.8% |
Prostate | M | 10,061 | ND1 | -1,890 | 18.8% |
Testis | M | 948 | ND2 | -1 | 0.1% |
Kidney | M | 1,603 | D1 | -175 | 10.9% |
F | 1,104 | D1 | -124 | 11.3% |
Bladder (invasive, insitu and uncertain behaviour) | M | 5,193 | D1 | 308 | 5.9% |
F | 2,298 | D1 | 108 | 4.7% |
Brain, meninges and CNS | M | 878 | D1 | -282 | 32.1% |
F | 729 | D1 | -82 | 11.2% |
Hodgkin's disease | M | 340 | D1 | 15 | 4.4% |
F | 288 | D1 | 18 | 6.3% |
NHL | M | 1,899 | ND1 | 430 | 22.6% |
F | 2,083 | D1 | 428 | 20.6% |
Leukaemia | M | 1,534 | D1 | 303 | 19.8% |
F | 1,298 | D1 | 308 | 23.8% |
Other and Unspecified | M | 7,242 | D1 | 1,625 | 22.4% |
F | 7,961 | D1 | 400 | 5.0% |
Total | | 130,417 | | 1,588 | 1.2% |
Note: Negative values denote underestimates« Previous | Contents | Next »