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Modelling Methodology
In modelling the costs to the NHS of treating smokers, a list of smoking-related diseases was established, including all conditions caused or severely aggravated by smoking.
The list of conditions was divided into quartiles, with diseases such as lung cancer in the top quartile given a probability of 0.875 that a patient suffering from this condition is a smoker or ex-smoker (diseases in the top quartile assume that 75%-100% of patients are smokers or ex-smokers and hence a mid-point probability of 0.875 is assigned).
Conditions falling into the bottom quartile of diseases were assigned a probability of 0.27, as this was the average prevalence rate of smoking among the wider population. The full range of smoking related diseases and assigned probabilities is shown in the table below.
| Smoking-related disease | Band | Percentage of patients who are smokers | Assigned probability patient is a smoker |
| Malignant neoplasm of base of tongue | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of bronchus and lung | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of gum | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of hypopharynx | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of larynx | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of lip | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of nasopharynx | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of oesophagus | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of oropharynx | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of palate | 1 | 75%-100% | 0.875 |
| Malignant neoplasm of trachea | 1 | 75%-100% | 0.875 |
| Duodenal ulcer | 2 | 50%-75% | 0.625 |
| Gastric ulcer | 2 | 50%-75% | 0.625 |
| Insulin-dependent diabetes mellitus | 2 | 50%-75% | 0.625 |
| Intracerebral haemorrhage | 2 | 50%-75% | 0.625 |
| Malignant neoplasm of floor of mouth | 2 | 50%-75% | 0.625 |
| Malignant neoplasm of other and unspecified parts of mouth | 2 | 50%-75% | 0.625 |
| Malignant neoplasm of other and unspecified parts of tongue | 2 | 50%-75% | 0.625 |
| Acute myocardial infarction | 3 | 25%-50% | 0.375 |
| Angina pectoris | 3 | 25%-50% | 0.375 |
| Asthma | 3 | 25%-50% | 0.375 |
| Atherosclerosis | 3 | 25%-50% | 0.375 |
| Atrial fibrillation and flutter | 3 | 25%-50% | 0.375 |
| Atrioventricular and left bundle-branch block | 3 | 25%-50% | 0.375 |
| Cerebral infarction | 3 | 25%-50% | 0.375 |
| Certain current complication follow acute myocardial infarction | 3 | 25%-50% | 0.375 |
| Chronic ischaemic heart disease | 3 | 25%-50% | 0.375 |
| Essential (primary) hypertension | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of bladder | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of kidney, except renal pelvis | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of pancreas | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of parotid gland | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of pyriform sinus | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of stomach | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of tonsil | 3 | 25%-50% | 0.375 |
| Malignant neoplasm of other & unspecified major saliva glands | 3 | 25%-50% | 0.375 |
| Myeloid leukaemia | 3 | 25%-50% | 0.375 |
| Non-insulin-dependent diabetes mellitus | 3 | 25%-50% | 0.375 |
| Occlusion/stenos precerebral arts not result cerebral infarction | 3 | 25%-50% | 0.375 |
| Occlusion/stenosis cerebral arts not result cerebral infarction | 3 | 25%-50% | 0.375 |
| Other acute ischaemic heart diseases | 3 | 25%-50% | 0.375 |
| Other cerebrovascular diseases | 3 | 25%-50% | 0.375 |
| Other chronic obstructive pulmonary disease | 3 | 25%-50% | 0.375 |
| Other disorders of urinary system | 3 | 25%-50% | 0.375 |
| Other nontraumatic intracranial haemorrhage | 3 | 25%-50% | 0.375 |
| Other peripheral vascular diseases | 3 | 25%-50% | 0.375 |
| Pain in throat and chest | 3 | 25%-50% | 0.375 |
| Sequelae of cerebrovascular disease | 3 | 25%-50% | 0.375 |
| Stroke, not specified as haemorrhage or infarction | 3 | 25%-50% | 0.375 |
| Heart failure | 4 | Average rate | 0.27 |
| Inguinal hernia | 4 | Average rate | 0.27 |
| Malignant neoplasm other ill-defined sites lip/oral cavity/pharynx | 4 | Average rate | 0.27 |
| Subarachnoid haemorrhage | 4 | Average rate | 0.27 |
| Subsequent myocardial infarction | 4 | Average rate | 0.27 |
On this basis, the number of people suffering from smoking-related diseases and who are likely to be smokers was calculated and used to determine the costs to the health service. Clearly, smokers will be treated for diseases other than the ones focused on in this research, but the impact of smoking on these other conditions was considered to be minimal and therefore not included. The costs are therefore the ‘additional costs’ smoking brings to the NHS.
The full list of conditions and their assigned probabilities was also compared to figures used in the Health Education Authority’s 1995 study, The Smoking Epidemic. The figures show that where direct comparisons can be drawn for individual cancer, circulatory and digestive diseases, the model used in this study is comparable to figures used in the 1995 HEA report (see full report for comparison).
As well as direct costs to the health service, Smoking Costs also considers several further sets of additional costs, including the cost of premature deaths of smokers from smoking, the costs of outpatient and follow-up appointments for smokers suffering from smoking-related diseases, the costs of lost earning time for those requiring hospital treatment and the costs of effects of second hand smoking.
In calculating the costs involved in each of these areas, the following definitions are used:
- Working life years: The number of years of life from 16-65 years old. A smoker dying from a smoking-related disease at 45 years of age would lose 20 working life years, for example.
- Pension life years: The number of life years between the end of the working life period and the average life expectancy. For men, this has been taken to be between 65 and 75 years of age; for women between 65 and 80.
- Cumulative costs: The total costs involved in the premature death of all smokers. This adds together the costs of all working life years and pension life years lost.
- Single life year: The next 12 month period of a smoker’s life. For example, if a smoker dies aged 52 and was in work, the single year costs would be the loss of the smoker’s earnings and associated costs to the local economy during the 12 months directly after the smoker’s death.