The tool uses estimates of the relative risk of death from any cause among regular cyclists or walkers, compared to people who do not cycle or walk regularly.
The tool is based on relative risk data from published studies. More details are available on the relative risks used in the HEAT for cycling and walking.
The tool uses these relative risks and applies them to the amount of walking or cycling entered by the user, assuming a linear relationship between walking/cycling and mortality.
To illustrate this, the relative risk from the meta-analysis used for the updated version of HEAT for cycling is 0.90 for regular commuter cycling for 100 minutes per week for 52 weeks of the year (equivalent to 87 hours of cycling per year) (see also section 3.2). Thus, in any given year, regular cyclists receive a protective benefit of 10% (1.00 minus 0.90) – that is, they are 10% less likely to die from any cause than non-cyclists. If the user enters a cycling volume equivalent to 29 hours per year (i.e. three times less), the protective benefit of this amount of cycling will be roughly 3%. If the user enters 174 hours (twice the time cycled in the reference population), the resulting protective benefit is 20%. This is twice the protective benefit of the reference population.
To avoid inflated values at the upper end of the range, the risk reduction available from the HEAT is capped. Inspection of the data points of the new meta-analyses suggested that, after about 45% risk reduction for cycling and 30% for walking, no significant further risk reductions were achieved. These limits were also confirmed by a large cohort study found through purposive review (1). On this basis, the advisory group recommended using these caps in the updated HEAT. Thus, HEAT will apply a maximum 45% risk reduction (corresponding to 447 minutes per week) in the risk of mortality for cycling and a maximum 30% risk reduction (corresponding to 460 minutes per week ) for walking.
Table: Summary of basic values used for HEAT
CI: confidence interval.
The HEAT then uses population level mortality data to estimate the number of adults who would normally be expected to die in any given year in the target population. Next, it calculates the reduction in expected deaths in this population that cycle or walk at the level specified by the user, using the adjusted relative risk.Finally, the tool produces an estimate of economic savings from this calculated reduction in deaths, as well as discounted and average savings.
*RR = relative risk of death in underlying studies (walking: 0.89; cycling: 0.90).
** Volume of cycling per person calculated based on 100 minutes per week for 52 weeks per year at an estimated speed of 14 km/hour. Volume of walking based on 168 minutes per week at 4.8 km/hour.