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Demand and capacity –
a comprehensive
guide
Online li
ary of Quality,
Service Improvement
and Redesign tools
NHS England and NHS Improvement
Demand and capacity –
a comprehensive guide
Quality, Service Improvement and Redesign Tools: Demand and capacity – a comprehensive guide
What is it?
In order to maximise patient flow through a healthcare system, you need to look at the
entire patient process. This guide helps you to understand the demand and capacity of a
system and what you can do if there is a mismatch between demand and capacity that
has resulted in a backlog.
Analysing the demand and capacity within a service will enable improvements to be made
that smooths the flow of service users through the system and helps to create a bette
patient and staff experience of the healthcare process. This is true regardless of whethe
you are looking at services providing inpatient, outpatient, community or mental health
services.
When to use it
Delays within systems occur when flow into the system is greater than flow out of the
system. Demand and capacity analysis allows you to identify the reasons for the delays
and the part of the system that is causing the backlog. If demand and capacity is
monitored on a regular basis, it provides a thorough understanding of flow through the
system, and allows service leaders to identify increasing waiting list lengths, bottlenecks
or constraints early on, to avoid possible future delays and the build-up of a backlog.
To do this, you need to have reliable measures for demand, capacity, activity and backlog
in place. This guide will outline a process for demand and capacity modelling from the
eginning, allowing you to undertake the initial analysis, after which point you can build
the measures into routine monitoring and service management.
How to use it
STEP 1: Define and identify demand, capacity, activity and backlog for the service.
Some hints on how to do this can be found below.
1.1 Demand: what we should be doing
All the requests
efe
als coming in from all sources, both electronic and paper-based,
and what resources they need (equipment time, staff time, room time) to be dealt with.
It is easy to miss some demand, especially if you are looking at a system that has a finite
capacity but demand which must be met within a short time-frame. For example:
• In an intensive care unit, the capacity is limited to the number of beds available.
When demand exceeds the number of beds available, something else must happen to
the service user such as them being transfe
ed to another hospital, or cared for on a
ward with support from a critical care outreach team. It is very important that any
demand that is not possible to meet is captured to provide an accurate reflection of
true demand.
• In a community setting hidden demand can reflect care which is self-refe
ed: if service
users are phoning and are either unable to get through or asked to phone back later,
rather than being put into an appointment or on a waiting list: this is hidden demand.
1.2 Capacity: what we could be doing
This refers to the resources available to do work. For example:
• In a diagnostic setting this might refer to any specialist equipment required, multiplied
by the hours of staff time available to run it.
• In a community setting services might depend on a multi-disciplinary team being
available, or something as simple as room availability. A particular challenge in relation
to this could be ensuring that capacity is focused in the right location, for example if
patient choice does not match the capacity provided, then it is possible that the
backlog for a service could grow despite having unused clinic slots.
• Another particular challenge in relation to capacity setting in some community and
mental health settings relates to the balance of ‘same day’ demand with regular
treatment. In these services there may not be a waiting list or backlog but there are
refe
als which need to be picked up and seen either the same day or within 48 hours,
alongside regular, planned work. Some organisations address this by ‘weighting’
each demand type/visit, and developing staffing rotas that ensure teams are safely
staffed with the right skills which can flex up and down when required.
Again it is important to look at actual capacity rather than ‘theoretical’ capacity.
Theoretical capacity can be calculated by looking at staff rotas and such, but there is
always a mismatch between theoretical capacity and actual capacity due to lots of
factors that may have not been taken into account. Particular elements that need to be
considered could be staff annual leave, mandatory and additional study leave, sickness,
time out for urgent meetings, travel time between service users (particularly in
community services), supervisions, management duties such as 1:1s and management
paperwork/HR and processes.
1.3 Activity: what we are actually doing
This refers to all the work done. This does not necessarily reflect capacity or demand on
a day-to-day basis. The activity or work done on a Monday may be the result of some of
Monday’s demand (ie emergency) and some ca
ied over from the previous weeks.
Activity data is usually more easily available than capacity or demand data, but it should
not be used instead of true capacity or demand data.
1.4 Backlog: what we should have done
This is previous demand that has not yet been dealt with, showing itself as a backlog of
work. A backlog is different to a waiting list, in that a backlog is unsustainable: it is the
mismatch between your demand and capacity, and means that the waiting list will keep
on growing, with service users waiting longer to be seen.
Quality, Service Improvement and Redesign Tools: Demand and capacity – a comprehensive guide
Figure 1: activity backlog capacity and demand
Once you have done these things you are ready to move onto the next steps.
STEP 2: Engage your stakeholders and process map
Map out the steps involved in the processes or service user pathways at a high level and
then in more detail so that you really understand what is going on. Map to the level of
what one person does, in one place, with one piece of equipment, at one time. The
process mapping tool will help you at this stage.
STEP 3. Identify the problems in your process map with your bottlenecks and
true constraint
3.1 Bottleneck(s): any part of the system where service user flow is obstructed causing
waits and delays.
The bottleneck is the step in the process where there are the longest delays for service
user at any part of the system where service user flow is obstructed, causing waits and
delays. It inte
upts the natural flow and hinders movement along the care pathway.
Quality, Service Improvement and Redesign Tools: Demand and capacity – a comprehensive guide
https:
improvement.nhs.uk
esources/process-mapping-conventional-model
However, there is usually something that is the actual cause of the bottleneck and this is
called the constraint. We often look at bottlenecks like a logjam in a river: it doesn’t
matter how much capacity is available after this particular step, because no furthe
interventions can commence until this step has happened, and it is this step that is
causing the delay.
3.2 Constraint(s): what restricts the capacity of the service at the bottleneck
The constraint is often a lack of availability of a specific skill or piece of equipment (eg
decontamination machine, CT scanner or specific surgical skills). Backlogs usually occu
efore the constraint in the process map and clear after the patient has gone past the
step with the constraint. Process templates are a visual representation of what
happens to one patient as they go through a process and help to identify the constraint
allowing you to support scheduling at the bottleneck.
STEP 4: Keep asking ‘why?’
In order to try and discover the real reason for the delay (see root cause analysis using
five whys). For example:
• The clinic always ove
uns and patients have to wait for a long time. Why? Because
the consultant does not have time to see all her patients in clinic. Why? Because she
has to see everyone who attends (including first visit assessments and follow up
patients). Why? It is what she has always done. Using the five whys tool will help
you to generate ideas for change that you can then act upon.
STEP 5: Measure your demand, capacity, backlog and activity in units of time
Based on the definitions described in Step 1, you can now move on to measure it, to
uild on your detailed process map for the patient journey you are focused on. Fo
comparison purposes, these should all be measured in the same units for the same
period of time, for example hourly, over a 24 hour period, weekly or monthly. It is also
important to compare the four measures on a single graph. This is important because
your team is likely to be one stage in the patient's pathway or journey. It is possible that
another team's work is the bottleneck. For example:
• In order to meet the four and twelve hour targets a lot of hospitals focused effort on
capacity in the accident and emergency department. However, assessment of the
patient pathway showed that one limiting factor was actually the completion of a
mental health assessment and subsequent availability of a mental health inpatient
bed. It was this subsequent lack of availability that slowed the ‘flow’ within the
pathway and caused the delay, not capacity within the A&E department specifically.
• In an outpatient setting the bottleneck may be a delay in the interpretation of a
diagnostic report, leading to a later outpatient appointment for treatment.
Quality, Service Improvement and Redesign Tools: Demand and capacity – a comprehensive guide
https:
improvement.nhs.uk
esources/process-templates
https:
improvement.nhs.uk
esources
oot-cause-analysis-using-five-whys
https:
improvement.nhs.uk
esources
oot-cause-analysis-using-five-whys
• In a community setting the constraint could be the availability of a domiciliary
physiotherapy service – meaning that any intervention required after physiotherapy is
delayed until this service can be provided in the patient’s home.
• In a mental health setting delays could be limited due to the capacity of staff
availability to undertake new patient assessments – following which they could be
streamed into a counselling service or group therapy, but the patient cannot enter the
waiting list for either of these until the initial assessment is complete, even if there is
capacity further down the pathway.
How to measure