<s>
In	O
statistics	O
and	O
machine	O
learning	O
,	O
leakage	B-General_Concept
(	O
also	O
known	O
as	O
data	B-General_Concept
leakage	I-General_Concept
or	O
target	B-General_Concept
leakage	I-General_Concept
)	O
is	O
the	O
use	O
of	O
information	O
in	O
the	O
model	O
training	O
process	O
which	O
would	O
not	O
be	O
expected	O
to	O
be	O
available	O
at	O
prediction	O
time	O
,	O
causing	O
the	O
predictive	O
scores	O
(	O
metrics	O
)	O
to	O
overestimate	O
the	O
model	O
's	O
utility	O
when	O
run	O
in	O
a	O
production	O
environment	O
.	O
</s>
<s>
Leakage	B-General_Concept
is	O
often	O
subtle	O
and	O
indirect	O
,	O
making	O
it	O
hard	O
to	O
detect	O
and	O
eliminate	O
.	O
</s>
<s>
Leakage	B-General_Concept
can	O
cause	O
a	O
statistician	O
or	O
modeler	O
to	O
select	O
a	O
suboptimal	O
model	O
,	O
which	O
could	O
be	O
outperformed	O
by	O
a	O
leakage-free	O
model	O
.	O
</s>
<s>
Leakage	B-General_Concept
can	O
occur	O
in	O
many	O
steps	O
in	O
the	O
machine	O
learning	O
process	O
.	O
</s>
<s>
The	O
leakage	B-General_Concept
causes	O
can	O
be	O
sub-classified	O
into	O
two	O
possible	O
sources	O
of	O
leakage	B-General_Concept
for	O
a	O
model	O
:	O
features	O
and	O
training	O
examples	O
.	O
</s>
<s>
Feature	O
or	O
column-wise	O
leakage	B-General_Concept
is	O
caused	O
by	O
the	O
inclusion	O
of	O
columns	O
which	O
are	O
one	O
of	O
the	O
following	O
:	O
a	O
duplicate	O
label	O
,	O
a	O
proxy	O
for	O
the	O
label	O
,	O
or	O
the	O
label	O
itself	O
.	O
</s>
<s>
These	O
features	O
,	O
known	O
as	O
anachronisms	O
,	O
will	O
not	O
be	O
available	O
when	O
the	O
model	O
is	O
used	O
for	O
predictions	O
,	O
and	O
result	O
in	O
leakage	B-General_Concept
if	O
included	O
when	O
the	O
model	O
is	O
trained	O
.	O
</s>
<s>
Row-wise	O
leakage	B-General_Concept
is	O
caused	O
by	O
improper	O
sharing	O
of	O
information	O
between	O
rows	O
of	O
data	O
.	O
</s>
<s>
Types	O
of	O
row-wise	O
leakage	B-General_Concept
include	O
:	O
</s>
<s>
Time	O
leakage	B-General_Concept
(	O
e.g.	O
</s>
<s>
Group	O
leakage	B-General_Concept
--	O
not	O
including	O
a	O
grouping	O
split	O
column	O
(	O
e.g.	O
</s>
