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Wednesday 15 July 2015

Making Better Decisions

Making Better Decisions

Making Better Decisions

Why do we analyse and present data?

Source: Robert Lloyd IHI 2006

To understand

the variation

that lives

within our data

To help us make

good management

decisions in the

way we react to

that variation

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Making Better Decisions

But often we have presented data in a different way ...

Making Better Decisions

We have 2 quarterly data points - is this an improvement?

Executive Time Series

0

20

40

60

80

100

J F M A M J J A S O N D

Months

So

meth

ing

Im

po

rtan

t

Higher is

better

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Making Better Decisions

Are we assuming something like this?

Executive Time Series - linear trend

0

20

40

60

80

100

J F M A M J J A S O N D

Months

So

meth

ing

Im

po

rtan

t

Making Better Decisions

But it could be like this ...

Executive Time Series - no trend

0

20

40

60

80

100

J F M A M J J A S O N D

Months

So

meth

ing

Im

po

rtan

t

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Making Better Decisions

Or this ...

Executive Time Series - seasonal dip

0

20

40

60

80

100

J F M A M J J A S O N D

Months

So

meth

ing

Im

po

rtan

t

Making Better Decisions

Or this!

Executive Time Series - one month blip

0

20

40

60

80

100

J F M A M J J A S O N D

Months

So

meth

ing

Im

po

rtan

t

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Walter A. Shewhart(early 1920’s, Bell Laboratories)

• While every process displays variation:

• some processes display only controlled variation (common cause)– stable, consistent pattern of variation

– constant causes/ “chance”

• while others display uncontrolled variation as well– pattern changes over time

– special cause variation/“assignable” cause

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Making Better Decisions

Shewhart’s purpose

• Data contains both signals and noise. To be able to extract information, one must separate the signal from the noise within the data.

To fulfill that purpose he created the control chart

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A statistical process control chart

0

10

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30

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70

80

F M A M J J A S O N D J F M A M J J A S O N D

Upper process

limit

Mean

Lower process

limit

Plot data in time order

Calculate and plot mean as a line

Calculate and plot process limits as lines

Analyse chart by studying how values fall around mean and limits

Making Better Decisions

How often to measure?Barnsley stroke pathway

time in hospital before getting onto stroke ward

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Making Better Decisions

Monthly data shows improvement

Average length of pre-ward stay on Barnsley

Stroke Ward

from 01/2007 to 07/2007

0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 6 7

Months

Weekly data tells a different story

Average length of pre-ward stay on Barnsley

Stroke Ward

from 01/2007 to 07/2007

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

1 3 5 7 9

11

13

15

17

19

21

23

25

27

29

31

Weeks

Making Better Decisions

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Patient level data adds another level of understanding

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SPC CHART RULES

Source: Lloyd Nelson, Technical Aids: The Shewhart Control Chart – Tests for Special Causes

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Upper control limit

Mean

Lower control limit

Rule # 1: Any single point outside the control limits

Upper control limit

Mean

Lower control limit

Rule # 2: A shiftAt least 7 points consecutively either above

or below the centre line

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Upper control limit

Mean

Lower control limit

Rule #3: A driftAt least 7 points consecutively ascending or

descending

Note: the points can cross the centre line

Upper control limit

Mean

Lower control limit

Rule #4:At least 14 points alternating up and down

Note: the points do not have to alternate above and below the centre line

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Mean

Mean+1V

Mean+2V

Mean+3V

Mean-1V

Mean-2V

Mean-3V

Upper control limit

Mean

Lower control limit

Other tests require you to plot the intermediate variation values

Mean

Mean+1V

Mean+2V

Mean+3V

Mean-1V

Mean-2V

Mean-3V

Upper control limit

Mean

Lower control limit

Rule #5:2 out of 3 points outside 2V on the same

side of the centre line

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Mean

Mean+1V

Mean+2V

Mean+3V

Mean-1V

Mean-2V

Mean-3V

Upper control limit

Mean

Lower control limit

Rule #6:4 out of 5 points outside 1V on the same

side of the centre line

Mean

Mean+1V

Mean+2V

Mean+3V

Mean-1V

Mean-2V

Mean-3V

Upper control limit

Mean

Lower control limit

Rule #7: Reduced variation15 points within 1V either side of the centre

line

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Mean

Mean+1V

Mean+2V

Mean+3V

Mean-1V

Mean-2V

Mean-3V

Upper control limit

Mean

Lower control limit

Rule #8: 2 processes8 points in a row on both sides of the

centre line with none within 1V

Making Better Decisions

Process 1

X

X

X

X X

XX

XX

XX

XX

X

X

X

X

X

X

X

X

PREDICTABLE? YES / NO / NOT SURERULE 1 2 3 4

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Making Better Decisions

Process 2

1 2 3 4 5 6 7 8

XX X

X

XX

X

X

X

X

XX X

X

X

X X

X

X

X

X

PREDICTABLE? YES / NO / NOT SURERULE 1 2 3 41 2 3 4 5 6 7 8

Making Better Decisions

Process 3

X

X

X

X

X

XX

X

X

X

XX

X

X

XX

X X X X

X

PREDICTABLE? YES / NO / NOT SURERULE 1 2 3 41 2 3 4 5 6 7 8

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Making Better Decisions

Process 4

X X X

X X

XX X X X

X

X

X X

X

X

X X

X

X X

PREDICTABLE? YES / NO / NOT SURE RULE 1 2 3 4 1 2 3 4 5 6 7 8

Making Better Decisions

Process 5

1 2 3 4 5 6 7 8

X

X

X

X

XX

X

X

X

X

X

X

X

XX

X

X

X

XX

X

PREDICTABLE? YES / NO / NOT SURERULE 1 2 3 41 2 3 4 5 6 7 8

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Making Better Decisions

Process 6

X

X X

X

X

XX

X

X XX

X

X

X

XX X

X

XX

X

PREDICTABLE? YES / NO / NOT SURERULE 1 2 3 41 2 3 4 5 6 7 8

What decision do you make?

Is your information presented in a way that allows you to confidently make one of these decisions?

Decision Because

Do nothing Performance ok

Contingency plans Special cause variation

Process redesign Common cause variation

Making Better Decisions

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Making Better Decisions

So why run or control charts?

• One picture, one message

• Shows change over time

• Allows you to see variation and differentiate between signal and noise

• Helps you to make the right decision

MRSA performance

City Hospital

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2

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17/0

1/0

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17/0

1/0

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1/0

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21/0

1/0

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01/0

2/0

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04/0

2/0

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10/0

2/0

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2/0

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24/0

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09/0

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17/0

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28/0

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03/0

5/0

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06/0

5/0

5

Date of event

Gap

betw

een

su

ccessiv

e e

ven

ts

Gap betw een specimens Average LCL UCL

Hospital X

Making Better Decisions

SPC tools

• Baseline

– http://www.valuesystemdesign.com

• Winchart from Prism Europe

– http://www.winchart.net/

• Chartrunner from PQ Systems

– http://www.pqsystems.com/products/SPC/CHARTrunner/CHARTrunner.php

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Making Better Decisions

Useful references

• Donald Wheeler. Understanding Variation. Knoxville: SPC Press Inc, 1995

• Donald Wheeler. Making sense of data. SPC for the service sector. Knoxville: SPC Press Inc, 2003

• WE Deming. Out of the crisis. Massachusetts: MIT 1986

• American Society for Qualitywww.asq.org/about/history/shewhart.html

• Donald M Berwick. Controlling variation in health care: a consultation from Walter Shewhart. Med Care 1991; 29: 1212-25.

• Walter A Shewhart. Economic control of quality of manufactured product. New York: D Van Nostrand 1931.