Statistical process control charts

and SAS

Ying Jiang

Health Quality Council

Saskatoon, SK

Outline

• Introduction

• SAS procedure

• Examples

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.

Application

• Monitor system and correct if needed

• Find and evaluate causes of variation

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.

SAS syntax

• PROC SHEWHART ;

SAS Syntax Demo: P chart

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

09

DEC20

09

FEB20

10

APR20

10

JUN20

10

AUG20

10

OCT20

10

DEC20

10

FEB20

11

APR20

11

JUN20

11

AUG20

11

OCT20

11

DEC20

11

FEB20

12

APR20

12

JUN20

12

JUL20

1240

50

60

70

80

90

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

Thanks!

Questions?