<s>
In	O
statistics	O
,	O
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
is	O
a	O
multiple	B-General_Concept
comparison	I-General_Concept
procedure	O
developed	O
by	O
Canadian	O
statistician	O
Charles	O
Dunnett	O
to	O
compare	O
each	O
of	O
a	O
number	O
of	O
treatments	O
with	O
a	O
single	O
control	O
.	O
</s>
<s>
Multiple	B-General_Concept
comparisons	I-General_Concept
to	O
a	O
control	O
are	O
also	O
referred	O
to	O
as	O
many-to-one	O
comparisons	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
was	O
developed	O
in	O
1955	O
;	O
an	O
updated	O
table	O
of	O
critical	O
values	O
was	O
published	O
in	O
1964	O
.	O
</s>
<s>
The	O
multiple	B-General_Concept
comparisons	I-General_Concept
,	O
multiplicity	O
or	O
multiple	B-General_Concept
testing	I-General_Concept
problem	I-General_Concept
occurs	O
when	O
one	O
considers	O
a	O
set	O
of	O
statistical	O
inferences	O
simultaneously	O
or	O
infers	O
a	O
subset	O
of	O
parameters	O
selected	O
based	O
on	O
the	O
observed	O
values	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
are	O
well	O
known	O
and	O
widely	O
used	O
in	O
multiple	B-General_Concept
comparison	I-General_Concept
procedure	O
for	O
simultaneously	O
comparing	O
,	O
by	O
interval	O
estimation	O
or	O
hypothesis	O
testing	O
,	O
all	O
active	O
treatments	O
with	O
a	O
control	O
when	O
sampling	O
from	O
a	O
distribution	O
where	O
the	O
normality	O
assumption	O
is	O
reasonable	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
is	O
designed	O
to	O
hold	O
the	O
family-wise	O
error	O
rate	O
at	O
or	O
below	O
when	O
performing	O
multiple	B-General_Concept
comparisons	I-General_Concept
of	O
treatment	O
group	O
with	O
control	O
.	O
</s>
<s>
The	O
original	O
work	O
on	O
Multiple	B-General_Concept
Comparisons	I-General_Concept
problem	I-General_Concept
was	O
made	O
by	O
Tukey	O
and	O
Scheffé	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
only	O
compares	O
one	O
group	O
with	O
the	O
others	O
,	O
addressing	O
a	O
special	O
case	O
of	O
multiple	B-General_Concept
comparisons	I-General_Concept
problem	I-General_Concept
—	O
pairwise	O
comparisons	O
of	O
multiple	O
treatment	O
groups	O
with	O
a	O
single	O
control	O
group	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
takes	O
into	O
consideration	O
the	O
special	O
structure	O
of	O
comparing	O
treatment	O
against	O
control	O
,	O
yielding	O
narrower	O
confidence	O
intervals	O
.	O
</s>
<s>
It	O
is	O
very	O
common	O
to	O
use	O
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
in	O
medical	O
experiments	O
,	O
for	O
example	O
comparing	O
blood	O
count	O
measurements	O
on	O
three	O
groups	O
of	O
animals	O
,	O
one	O
of	O
which	O
served	O
as	O
a	O
control	O
while	O
the	O
other	O
two	O
were	O
treated	O
with	O
two	O
different	O
drugs	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
is	O
performed	O
by	O
computing	O
a	O
Student	O
's	O
t-statistic	O
for	O
each	O
experimental	O
,	O
or	O
treatment	O
,	O
group	O
where	O
the	O
statistic	O
compares	O
the	O
treatment	O
group	O
to	O
a	O
single	O
control	O
group	O
.	O
</s>
<s>
The	O
formal	O
test	O
statistic	O
for	O
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
is	O
either	O
the	O
largest	O
in	O
absolute	O
value	O
of	O
these	O
t-statistics	O
(	O
if	O
a	O
two-tailed	O
test	O
is	O
required	O
)	O
,	O
or	O
the	O
most	O
negative	O
or	O
most	O
positive	O
of	O
the	O
t-statistics	O
(	O
if	O
a	O
one-tailed	O
test	O
is	O
required	O
)	O
.	O
</s>
<s>
In	O
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
we	O
can	O
use	O
a	O
common	O
table	O
of	O
critical	O
values	O
,	O
but	O
more	O
flexible	O
options	O
are	O
nowadays	O
readily	O
available	O
in	O
many	O
statistics	O
packages	O
.	O
</s>
<s>
Dunnett	B-General_Concept
's	I-General_Concept
test	I-General_Concept
's	O
calculation	O
is	O
a	O
procedure	O
that	O
is	O
based	O
on	O
calculating	O
confidence	O
statements	O
about	O
the	O
true	O
or	O
the	O
expected	O
values	O
of	O
the	O
differences	O
,	O
thus	O
the	O
differences	O
between	O
treatment	O
groups	O
 '	O
mean	O
and	O
control	O
group	O
's	O
mean	O
.	O
</s>
