<s>
In	O
econometrics	O
,	O
Kwiatkowski	O
–	O
Phillips	O
–	O
Schmidt	O
–	O
Shin	O
(	O
KPSS	O
)	O
tests	O
are	O
used	O
for	O
testing	O
a	O
null	B-General_Concept
hypothesis	I-General_Concept
that	O
an	O
observable	O
time	O
series	O
is	O
stationary	B-Algorithm
around	O
a	O
deterministic	O
trend	O
(	O
i.e.	O
</s>
<s>
trend-stationary	O
)	O
against	O
the	O
alternative	O
of	O
a	O
unit	O
root	O
.	O
</s>
<s>
Contrary	O
to	O
most	O
unit	B-General_Concept
root	I-General_Concept
tests	I-General_Concept
,	O
the	O
presence	O
of	O
a	O
unit	O
root	O
is	O
not	O
the	O
null	B-General_Concept
hypothesis	I-General_Concept
but	O
the	O
alternative	O
.	O
</s>
<s>
Additionally	O
,	O
in	O
the	O
KPSS	B-General_Concept
test	I-General_Concept
,	O
the	O
absence	O
of	O
a	O
unit	O
root	O
is	O
not	O
a	O
proof	O
of	O
stationarity	B-Algorithm
but	O
,	O
by	O
design	O
,	O
of	O
trend-stationarity	O
.	O
</s>
<s>
This	O
is	O
an	O
important	O
distinction	O
since	O
it	O
is	O
possible	O
for	O
a	O
time	O
series	O
to	O
be	O
non-stationary	B-Algorithm
,	O
have	O
no	O
unit	O
root	O
yet	O
be	O
trend-stationary	O
.	O
</s>
<s>
In	O
both	O
unit	O
root	O
and	O
trend-stationary	O
processes	O
,	O
the	O
mean	O
can	O
be	O
growing	O
or	O
decreasing	O
over	O
time	O
;	O
however	O
,	O
in	O
the	O
presence	O
of	O
a	O
shock	O
,	O
trend-stationary	O
processes	O
are	O
mean-reverting	O
(	O
i.e.	O
</s>
<s>
Later	O
,	O
Denis	O
Kwiatkowski	O
,	O
Peter	O
C	O
.	O
B	O
.	O
Phillips	O
,	O
Peter	O
Schmidt	O
and	O
Yongcheol	O
Shin	O
(	O
1992	O
)	O
proposed	O
a	O
test	O
of	O
the	O
null	B-General_Concept
hypothesis	I-General_Concept
that	O
an	O
observable	O
series	O
is	O
trend-stationary	O
(	O
stationary	B-Algorithm
around	O
a	O
deterministic	O
trend	O
)	O
.	O
</s>
<s>
KPSS-type	O
tests	O
are	O
intended	O
to	O
complement	O
unit	B-General_Concept
root	I-General_Concept
tests	I-General_Concept
,	O
such	O
as	O
the	O
Dickey	B-General_Concept
–	I-General_Concept
Fuller	I-General_Concept
tests	I-General_Concept
.	O
</s>
<s>
By	O
testing	O
both	O
the	O
unit	O
root	O
hypothesis	O
and	O
the	O
stationarity	B-Algorithm
hypothesis	O
,	O
one	O
can	O
distinguish	O
series	O
that	O
appear	O
to	O
be	O
stationary	B-Algorithm
,	O
series	O
that	O
appear	O
to	O
have	O
a	O
unit	O
root	O
,	O
and	O
series	O
for	O
which	O
the	O
data	O
(	O
or	O
the	O
tests	O
)	O
are	O
not	O
sufficiently	O
informative	O
to	O
be	O
sure	O
whether	O
they	O
are	O
stationary	B-Algorithm
or	O
integrated	O
.	O
</s>
