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Statistical process control chart
• Shewhart chart;
• In statistical process control,
used to distinguish between
variation due to common
causes and variation due to
special causes;
What does it look like?
X Axis: Sequence of data
Y Axis:
measure
Data Points (each
dot is “subgroup”) 3 sigma limits
3 sigma limits
Provost L, Murray S. The Healthcare Data Guide: Learning from Data for
Improvement. San Francisco: Jossey-Bass, Publication, 2011.
Types of Charts
• Classification data: P chart
• Count data: C chart or U chart
• Continuous data: I chart or X bar
and S chart
Rules for Detecting Special Cause
Health care system
Provost L, Murray S. The Healthcare Data Guide: Learning from Data
for Improvement. San Francisco: Jossey-Bass, Publication, 2011.
Chart Formula
P chart
𝑷𝒃𝒂𝒓 = 𝒑
𝒌*100
𝝈𝒑 =𝑷𝒃𝒂𝒓 ∗ (𝟏𝟎𝟎 − 𝑷𝒃𝒂𝒓)
𝒏
k=Number of subgroups
n=Number of sample units per subgroup
Quality Insight Online
http://www.qualityinsight.ca/indicators?key=5fd61a52e57954d63745
485b0b4d7cac
Evaluation %
Alw
ays
All Saskatchewan Hospitalsp chart
UCL = 70.86CTL = 67.83LCL = 64.80
Ca
use
Ca
use
Ca
use
Ca
use
RTC StartsTC1 TC2 TC3
FEB20
09
APR20
09
JUN20
09
AUG20
09
OCT20
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DEC20
09
FEB20
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APR20
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JUN20
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AUG20
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OCT20
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DEC20
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FEB20
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APR20
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JUN20
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AUG20
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OCT20
11
DEC20
11
FEB20
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APR20
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JUN20
12
JUL20
1240
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60
70
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References
• Provost L, Murray S. The Healthcare Data
Guide: Learning from Data for Improvement.
San Francisco: Jossey-Bass, Publication, 2011.
• SAS/QC(R) 9.2 User's Guide
http://support.sas.com/documentation/cdl/en/q
cug/63922/HTML/default/viewer.htm#shewha
rt_toc.htm