Quality Management 2017
A NALYZE
13. Control charts building: EWMA
Type of drifts to detect
Control charts
Part 1 :
Introduction to SPC
Ex.: wrong adjustment of linac’s parameters, errors during measurement…
Large and Fast
Individual value / Moving Range Individual va o i nge
(I,MR)
Part 2 :
Patient number
Diff. mes/calc. (%)
Essential concepts to start with SPC
EWMA - Exponentially Weighted Moving Average -
Ex.: drift of the detector’s dose response
Small and slow
Part 3 :
Patient number Diff. mes/calc. (%)
SPC in practice
Building EWMA control chart
coefficient
coefficient
Ex: = 0.2 Importance of 20% for x i (current value) Importance of 80% for M i-1 (previous values)
M
M) 1( x
i
i
1i
Part 4
Conclusion
Current value Previous values
M
value current
values previsous
2.0
8.0
03/10/17
i
32
0
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