Queue, Demand, Capacity,
Variation and Flow
Essential measures for clinicians
and managers
The queue
• Queues occur where demand has not
been dealt with resulting in a backlog of
work.
• The main reasons why queues develop
is the mismatch between the variation
in demand and capacity at specific
times
The queue
• The NHS is a classic queue system
• We place patients in queues all the time
• some patients are in multiple queues
The queue
• Every time the demands exceeds the
capacity a queue is formed but
• Whenever capacity exceeds demand the
extra capacity is lost or it is filled from the
queue – often at short notice
• Filling slots at short notice can lead to longer
waiting times and distort clinical priorities
Managing the queue - using
evidence based tools
• Ensure an element of patient choice in
the booking process
• Use referral information services or
referral management services
• Ensure waiting list data is accurate
• Reduce unnecessary “carve out”
Managing the queue
• Take unnamed referrals –refer to a
service not a clinician
• Pool referrals
• Pool waiting lists
• See people in clinical and date order
Defining demand, capacity
activity and queue
• Demand on the services is all the requests or
referrals into the service from all sources
• Capacity is all of the resources required to do
the work and includes staff and equipment
• Activity is the work done, it is the throughput
of the system
• Backlog is the demand which has not been
dealt with – the queue or waiting list
Demand and capacity
definitions:
Waiting list, queue
Demand
= what we should have done
= All requests
for a service
=
what we should do
Capacity
= what we could do
Activity
= what we did
Measuring demand, capacity
activity and queue
• Why is it important to understand the four measures
of demand, capacity, activity and queue?
• To identify the bottleneck or constraint in the care
process
• To increase capacity at the stage of the process
where it will create the greatest outcome
• To reduce inappropriate demand to the constraint
• To redesign services or plan services
Measuring demand, capacity,
activity and queue
• Must be measured in the same units of time
for the same period i.e. hourly, over a 24 hour
period, weekly or monthly
• It is not possible to compare two or more
items unless they are measured in the same
unit of time
• It is important to compare the four measures
on a single graph
Measure demand
• Multiply the number of patients referred
from all sources by the time taken in
minutes to process a patient
• Understand your demand – what it is
(shape) and where it comes from
(source)
Manage demand
• Right person, right place, right time
• Understand and manage activity and
capacity to meet changes in demand
i.e. seasonal variation
Measure capacity
• Multiply the number of pieces of
equipment by the time available in
minutes available to the people with the
necessary skills to use it
Measure activity
• Multiply the number of patients
processed by the time in minutes it took
to process each patient
Measure the backlog or queue
• Multiply the number of patients waiting
by the time it will take in minutes to
process a patient
Compare the four measures
• Convert the data on demand, capacity,
activity and backlog or queue onto a
common line graph
If av. Demand = av. Capacity,
variation mismatch = queue
Queue
Capacity
Demand
Can’t pass
unused capacity
forward
time
demand
capacity
activity
80% of variation in demand
900
800
700
600
500
400
300
200
100
0
Sep-04 Oct-04 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05
Jul-05 Aug-05
Understanding flow
• In the NHS flow is the movement of patients,
information or equipment between
departments, staff groups or organisations as
part of their pathway of care
• Whilst process mapping looks at care
processes from the patients perspective, flow
analysis looks at the care process from a unit
or departmental perspective
Flow modelling
• Supports service improvement – at specific
bottlenecks or constraints, in specific clinical
areas, or across whole health systems
• This tool will not tell you what should change
– process mapping helps with identifying that
• Flow modelling will show how well scarce
resources are being used and how much
room there is for improvement
How to build the flow model
• Define the patient group to be analysed and
define the start and end points of the flow
map
• In straightforward care processes a process
map and process times will provide sufficient
information to examine patient flow
• The Unscheduled Care Collaborative made
extensive use of flow mapping and modelling
Understanding variation
• Why is it important to understand
variation
• Because the mismatch between the
variation in demand and capacity is one
of the main reasons that queues occur
in the NHS
What variability?
• GP
– Number of patients
– Number of problems
– Investigations
– Length of appointments
What variability?
• Outpatients
– Number of referrals
– Number of staff
– Investigations needed
– Length of consultation
What variability?
• Ward
-Length of pre-admission stay
-Length of post-op stay
-Intensity of nursing required
-Staffing levels
Variability
• Theatre
– Number of cases
– Length of cases
– Anaesthetic time
– Recovery time
– Turnaround time
Bed availability - an example of the
problem of variation
ADMISSION
Variation in
Admission Patterns
- particularly for
Elective Care
IN-PATIENT STAY
DISCHARGE
Variation in patient
pathways and
processes.
E.g. in Length of Stay
Variation in Discharge
- By time of day
- By day of week
- Seasonal variations
“We always bring
our hips in on Tuesday !”
ADMISSION
Variation in
Admission Patterns
- particularly for
Elective Care
IN-PATIENT STAY
DISCHARGE
Variation in patient
pathways and
processes.
E.g. in Length of
Stay
Variation in Discharge
- By time of day
- By day of week
- Seasonal variations
Understanding demand and
capacity by hour of the day
Emergency Demand - Decision to admit/hour
6
5
4
3
2
1
Time of day
23
21
19
17
15
13
11
9
7
5
3
0
1
Emergency Demand
7
Discharged patients/hour
12
10
8
6
4
2
Time of day
23
21
19
17
15
13
11
9
7
5
3
0
1
Discharged Patients
14
11/11/2002
28/10/2002
14/10/2002
30/09/2002
16/09/2002
02/09/2002
19/08/2002
05/08/2002
22/07/2002
08/07/2002
24/06/2002
10/06/2002
27/05/2002
13/05/2002
29/04/2002
15/04/2002
01/04/2002
Number of Admissions
Emergency & Elective Admissions
April-November 2002
60
50
40
30
Emergency
Admissions
20
Elective
Admissions
10
0
Analysing variation
• Statistical Process Control
• Two types of variation
• Common cause – that which is natural
and to be expected
• Special cause – which produces
unusual or unexpected variation
Statistical process control
• Two basic charts
• The run chart – a line graph – an ideal
method of comparing sets of data
• The control chart – also run charts but
with two distinct differences i.e.
Any questions?