365 / 879
1i
i
i
M) 1( x
M
Current value Previous values
coefficient
coefficient
Building EWMA control chart
Ex:
= 0.2
Importance of 20% for x
i
(current value)
Importance of 80% for M
i-1
(previous values)
32
13. Control charts building: EWMA
Part 1
:
Introduction to
SPC
Part 2
:
Essential
concepts to
start with SPC
Part 4
Conclusion
Part 3
:
SPC in
practice
A
NALYZE
Individual value
/
Moving Range
Type of drifts to detect
Control charts
Small
and
slow
Ex.: wrong
adjustment of linac’s
parameters, errors
during
measurement…
Ex.: drift of the
detector’s dose
response
Diff. mes/calc. (%)
Patient number
EWMA
- Exponentially
Weighted Moving
Average -
Patient number
Diff. mes/calc. (%)
Large
and
Fast
(I,MR)
Individual va
o i
nge
0
values
previsous
value
current
M
i
8.0
2.0
03/10/17