<s>
In	O
statistical	O
quality	O
control	O
,	O
the	O
EWMA	B-Application
chart	I-Application
(	O
or	O
exponentially	O
weighted	O
moving	O
average	O
chart	O
)	O
is	O
a	O
type	O
of	O
control	B-General_Concept
chart	I-General_Concept
used	O
to	O
monitor	O
either	O
variables	O
or	O
attributes-type	O
data	O
using	O
the	O
monitored	O
business	O
or	O
industrial	O
process	O
's	O
entire	O
history	O
of	O
output	O
.	O
</s>
<s>
While	O
other	O
control	B-General_Concept
charts	I-General_Concept
treat	O
rational	O
subgroups	O
of	O
samples	O
individually	O
,	O
the	O
EWMA	B-Application
chart	I-Application
tracks	O
the	O
exponentially-weighted	O
moving	O
average	O
of	O
all	O
prior	O
sample	O
means	O
.	O
</s>
<s>
Although	O
the	O
normal	O
distribution	O
is	O
the	O
basis	O
of	O
the	O
EWMA	B-Application
chart	I-Application
,	O
the	O
chart	O
is	O
also	O
relatively	O
robust	O
in	O
the	O
face	O
of	O
non-normally	O
distributed	O
quality	O
characteristics	O
.	O
</s>
<s>
The	O
EWMA	O
control	B-General_Concept
chart	I-General_Concept
requires	O
a	O
knowledgeable	O
person	O
to	O
select	O
two	O
parameters	O
before	O
setup	O
:	O
</s>
<s>
L	O
is	O
typically	O
set	O
at	O
3	O
to	O
match	O
other	O
control	B-General_Concept
charts	I-General_Concept
,	O
but	O
it	O
may	O
be	O
necessary	O
to	O
reduce	O
L	O
slightly	O
for	O
small	O
values	O
of	O
λ	O
.	O
</s>
<s>
Instead	O
of	O
plotting	O
rational	O
subgroup	O
averages	O
directly	O
,	O
the	O
EWMA	B-Application
chart	I-Application
computes	O
successive	O
observations	O
zi	O
by	O
computing	O
the	O
rational	O
subgroup	O
average	O
,	O
,	O
and	O
then	O
combining	O
that	O
new	O
subgroup	O
average	O
with	O
the	O
running	O
average	O
of	O
all	O
preceding	O
observations	O
,	O
zi	O
-	O
1	O
,	O
using	O
the	O
specially	O
–	O
chosen	O
weight	O
,	O
λ	O
,	O
as	O
follows	O
:	O
</s>
<s>
The	O
EWMA	B-Application
chart	I-Application
is	O
sensitive	O
to	O
small	O
shifts	O
in	O
the	O
process	O
mean	O
,	O
but	O
does	O
not	O
match	O
the	O
ability	O
of	O
Shewhart-style	O
charts	O
(	O
namely	O
the	O
and	O
R	O
and	O
and	O
s	O
charts	O
)	O
to	O
detect	O
larger	O
shifts	O
.	O
</s>
<s>
One	O
author	O
recommends	O
superimposing	O
the	O
EWMA	B-Application
chart	I-Application
on	O
top	O
of	O
a	O
suitable	O
Shewhart-style	O
chart	O
with	O
widened	O
control	O
limits	O
in	O
order	O
to	O
detect	O
both	O
small	O
and	O
large	O
shifts	O
in	O
the	O
process	O
mean	O
.	O
</s>
