<s>
In	O
statistics	O
,	O
probability	B-General_Concept
density	I-General_Concept
estimation	I-General_Concept
or	O
simply	O
density	B-General_Concept
estimation	I-General_Concept
is	O
the	O
construction	O
of	O
an	O
estimate	O
,	O
based	O
on	O
observed	O
data	O
,	O
of	O
an	O
unobservable	O
underlying	O
probability	O
density	O
function	O
.	O
</s>
<s>
A	O
variety	O
of	O
approaches	O
to	O
density	B-General_Concept
estimation	I-General_Concept
are	O
used	O
,	O
including	O
Parzen	B-General_Concept
windows	I-General_Concept
and	O
a	O
range	O
of	O
data	B-Algorithm
clustering	I-Algorithm
techniques	O
,	O
including	O
vector	B-Algorithm
quantization	I-Algorithm
.	O
</s>
<s>
The	O
most	O
basic	O
form	O
of	O
density	B-General_Concept
estimation	I-General_Concept
is	O
a	O
rescaled	O
histogram	B-Algorithm
.	O
</s>
<s>
The	O
following	O
is	O
quoted	O
verbatim	O
from	O
the	O
data	B-General_Concept
set	I-General_Concept
description	O
:	O
</s>
<s>
The	O
"	O
glu	O
"	O
data	O
were	O
obtained	O
from	O
the	O
MASS	O
package	O
of	O
the	O
R	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Within	O
R	B-Language
,	O
?	O
Pima.tr	O
and	O
?	O
Pima.te	O
give	O
a	O
fuller	O
account	O
of	O
the	O
data	O
.	O
</s>
<s>
From	O
this	O
we	O
see	O
that	O
,	O
in	O
this	O
data	B-General_Concept
set	I-General_Concept
,	O
diabetes	O
cases	O
are	O
associated	O
with	O
greater	O
levels	O
of	O
"	O
glu	O
"	O
.	O
</s>
<s>
The	O
density	O
estimates	O
are	O
kernel	B-General_Concept
density	I-General_Concept
estimates	I-General_Concept
using	O
a	O
Gaussian	O
kernel	O
.	O
</s>
<s>
A	O
very	O
natural	O
use	O
of	O
density	O
estimates	O
is	O
in	O
the	O
informal	O
investigation	O
of	O
the	O
properties	O
of	O
a	O
given	O
set	B-General_Concept
of	I-General_Concept
data	I-General_Concept
.	O
</s>
<s>
Density	B-General_Concept
estimation	I-General_Concept
is	O
also	O
frequently	O
used	O
in	O
anomaly	B-Algorithm
detection	I-Algorithm
or	O
novelty	B-Algorithm
detection	I-Algorithm
:	O
if	O
an	O
observation	O
lies	O
in	O
a	O
very	O
low-density	O
region	O
,	O
it	O
is	O
likely	O
to	O
be	O
an	O
anomaly	O
or	O
a	O
novelty	O
.	O
</s>
<s>
In	O
hydrology	O
the	O
histogram	B-Algorithm
and	O
estimated	O
density	O
function	O
of	O
rainfall	O
and	O
river	O
discharge	O
data	O
,	O
analysed	O
with	O
a	O
probability	O
distribution	O
,	O
are	O
used	O
to	O
gain	O
insight	O
in	O
their	O
behaviour	O
and	O
frequency	O
of	O
occurrence	O
.	O
</s>
