QuEST Mental Health Data for
Improvement Network
SPC Charts
Alison Redpath
Senior Information Analyst
Statistical Process Control (SPC)
Run Chart vs SPC
Run Chart
SPC
Displays data as a picture that shows variation over time
Simple rules make it easy to spot and interpret patterns (and not over interpret)
Shows signals of change
Is more sensitive and shows special
causes of variation
Enables you to see the individual data points and the average at the same time
Shows the natural range, useful in
planning
Needs small amount of data
Need 20-30 data points as a minimum
One way to create
Many different types exist
Which chart?
Continuous
Discrete
What type
of data?
How many
observations
per subgroup?
No
Can both
occurrences and
non-occurrences
be counted?
Yes
Are there equal
areas of
opportunity?
2-10
1
XbarR chart
>10
XbarS chart
XmR chart
Yes
c-chart
No
u-chart
Are the subgroups equal
size?
No
p-chart
Yes
np-chart
Which chart?
Measure
Count
What type
of data?
How many are
represented by
one data
point?
No
Do we have both
pass/fail, yes/no?
Yes
Is the chance
the same for
each point?
2-10
1
Yes
>10
XbarR chart
No
XmR chart
XbarS chart
c-chart
u-chart
Do all data
points
represent the
same number?
No
p-chart
Yes
np-chart
Mental Health likely charts
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Waiting times breachers per month % p-chart
DNA % - p-chart
New:follow-up ratio per month p-chart
Number of referrals per month c-chart
Number of patients on the caseload per month c-chart
Total waiting list size c-chart
Average waiting time per month XbarR chart
Average waiting time per day XbarS chart
Waiting time per patient XmR chart
Method
Equations
https://www.moresteam.com/toolbox/statistical-process-control-spc.cfm
Theory
Rules for interpretation
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•
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Any point outside the control limits
2/3 points in the outer third
15 consecutive points in the inner third
8 or more above or below the average
6 or more in a trend
Example
• Number of Adult Psychiatry Appointments DNA'd in NHS
Somewhere between January 2011 and January 2013
Example
Further information
• http://en.wikipedia.org/wiki/Control_chart has
a list of different control chart types, with links
to how to construct each of them
• Register with IHI.org and then find the webex
On Demand: Using Run and Control Charts to
Understand Variation
Further support
Alison Redpath
Senior Information Analyst
QuEST Mental Health
01312443284
alison.pickering@scotland.gsi.gov.uk