Defining Abstraction

When running an operation that uses resources, there is a distinction between the number of people that you employ and the number that will be available at any one time. The difference between these two numbers is referred to as ‘Abstraction’.  When modelling Emergency Services processes it is important to account for the time that resources are not available. In this case abstraction is defined as ‘the act of taking away or separating’.


What is typically counted as Abstraction?

Typically the following elements would almost always be counted as abstraction

  • Annual Leave
  • Sickness
  • Training

Annual Leave: Typically the amount of annual leave that an employee is entitled to will be stipulated within their contract. In some organisations leave entitlement may increase in line with length of service. In these cases it is suggested that taking a weighted average of the leave entitlement based on length of service will give a good indication of annual leave levels. Bank holidays should also be factored into the Annual Leave figure, as staff will be entitled to the bank holidays even though they may work on these days to allow for the 24/7 coverage required in many parts of  Emergency Services operations.

Sickness Levels: Sickness levels vary between forces and particularly between different functions of organisations. There is some evidence to suggest a tendency to see higher levels of sickness in front-line functions such as Response Policing.Sickness is generally measured as a proportion of the overall time on shift that is missed. Aggregating the number of hours missed and dividing by the time on shift would give a good indication of sickness levels. When modelling sickness levels it is important to strike a balance between getting a sickness level that is representative for a department while not inputting a sickness number that plans for higher sickness. For example if a Police Response function currently has a sickness rate of 12% yet the Force average was only 5%, then there would be a judgement call as to whether the 12% represents the stresses and strains of working in that particular area, or whether it is an anomaly and requires a larger sample period to demonstrate a representative sickness proportion.

Published Long-term sickness rates range from 0.5% to around 4% at a Force level, but may be much higher in certain departments, with Response tending to see higher levels.

Sickness levels can have a substantial impact on the resource requirements that departments need. For example, some Police Forces have looked at having an Incident Assessment Unit within their Contact Management function and had earmarked this as potentially a productive way to utilise restricted and recuperative officers. Although this makes sense in principle, by the very nature of the officers that would be in the team, the levels of abstraction would be higher, therefore calculations would have to factor this in, requiring more officers to conduct the workload. In a similar vein, understanding the effect that restrictions placed on officers after complaint may also need to be included.

Training: Depending on the function and rota set up, some departments will have dedicated training days, while for others these are more ad hoc. Typically Police Officers would have between 5-10 days training per year, during this time they are removed from their current role and should be considered within abstraction.


Other Considerations when calculating Resource requirement

Depending on the role and department there are other factors that may be considered when calculating resource requirements from a workload. These include:

  • Refreshment Breaks – if not explicitly modelled then should be considered
  • Vacancy Rates – if the expectation is that the department will always run below its budgeted headcount then applying a vacancy rate may be appropriate
  • Overtime consideration – when modelling how many resources are required to deal with a specific workload, it is important to recognise the impact overtime is currently having on productivity.
    • For example, if a team of 10 FTE are currently clearing 1,000 tasks per year but are only achieving this with 10% overtime, then it would be suggested that the throughput of 10FTE is actually 900 tasks per year.

What levels of abstractions should I expect?

Abstraction levels very much depend on the department that is being modelled and the structures in place. In a Call Handling environment abstraction levels can be as low as 22%, while in Response teams the levels can rise to 40% in some areas.

For any advice on how to model your abstraction or any questions around the methodology, please contact us at