The method involved four steps:
- Identification of diseases where physical inactivity is a risk factor;
- Calculation of the total numbers of deaths and the DALYs lost for these diseases;
- Identification of the population attributable fractions (PAFs) for each disease;
- Application of these PAFs to National Health Service (NHS) cost data, to calculate the direct costs of physical inactivity to the NHS
A PAF indicates the proportion of disease that can be attributed to a particular risk factor. The World Health Report calculated the PAF due to physical inactivity against a theoretical population in which all individuals participated in regular physical activity defined as being physically active in any of the four domains of work, transport, domestic duties or during leisure time.3
The cost, or burden, of an illness can be measured by the loss of duration and quality of life, and by the financial impact of related disease on the health system (direct costs) and on society (indirect costs). Mortality provides a clear measure of the overall loss of life due to specific diseases and is relatively easy to measure when mortality records are accurate. The burden of disease can be measured by its effect on the duration and quality of life using DALYs; an aggregate measure derived from years of life lost to premature death (YLL) and the years of life impeded by disability (YLD). Estimates of the burden of disease attributable to 10 major risk factors were produced by the global burden of disease project.9
The risk factors were tobacco, alcohol, illicit drugs, occupation, air pollution, poor water supply, poor sanitation and hygiene, hypertension, physical inactivity, malnutrition and unsafe sex.
We relied on data from the World Health Organisation (WHO) both for mortality and disability measures and for PAF estimates. As such we were constrained by the limitations of the burden of disease project. Data on mortality, YLL, YLD and DALYs were taken from the World Health Report3
for European countries with very low child and very low adult mortality (WHO region EUR‐A). We used the diseases defined by the WHO as having some relationship with physical inactivity—ischaemic heart disease, ischaemic stroke, breast cancer, colon/rectum cancer and diabetes mellitus. Although the WHO project provides a PAF for ischaemic stroke, data on DALYs, YLLs and YLDs are available only at the level of cerebrovascular diseases; this category was used as a surrogate for ischaemic stroke.3
In addition, the WHO list of attributable diseases was shorter than others13,14
and did not include other factors such as osteoporosis.
We used the published PAF to calculate the mortality, YLL, YLD and DALYs attributable to physical inactivity within WHO region EUR‐A for broad disease categories and for each disease linked to physical inactivity. The number of deaths owing to physical inactivity in the UK was calculated by applying PAFs to mortality data.1
In 1996, the National Health Executive10
published a study which ascribed NHS costs 1992–3 to the International Classification of Disease (ICD) 9 codes. This report represents the most recent detailed estimate of NHS costs by ICD codes. NHS total cost was defined as the sum of NHS in‐patient and out‐patient costs, NHS primary care expenditure, NHS pharmaceutical expenditure and NHS net community care services expenditure for the year 1992–3. NHS expenditure by disease code in 1992–3 was applied to the 2002 NHS total to provide an estimate of costs per disease for 2002. The cost of physical inactivity was calculated by applying the PAFs for diseases related to physical inactivity to 2002 disease‐specific costs.