62
A. P. Layton and M. Katsuura
a method for predicting the dates of turning points. This
contrasts with other earlier approaches to turning point
prediction which have used the estimated regime state
probabilities arising from a constant transition parameter
regime switching model. This paper attempts to extract use-
ful information from the estimated time-varying transition
probabilities. The switching probability from contraction
into expansion, p12t, isused as the basis for signalsof troughs,
and p21t, the switching probability from expansion into con-
traction, is used as the basis for the signals of peaks.
In previous papers using regime state probabilities (as
opposed to the transition probabilities used here) the rule
adopted for dating peaks and troughs related to the state
probability being above or below 0.5 (see Hamilton, 1989;
Layton, 1996, 1997a). In this context, the problem is to
determine a similar cut-oŒ value for the relevant transition
probability which may reasonably be regarded as high
enough to be treated as a trigger signal of an imminent
phase change. A natural selection is the overall long term
mean value of the transition parameter.7 This then is one
aspect of the signal.
where r ¶ 5. The constraint r ¶ 5 is selected to be analo-
gous to a similar requirement in the long standing and
widely-used Bry±Bochan method8 for determining turning
points and which incorporates the requirement that no
phase will be recognized if it has a duration less than ®ve
months. By de®nition, the occurrence of the local minimum
leads the signal expressed by Equations 5 and 6. Therefore,
it may be regarded as the ®rst tentative signal of an
impending turning point. Of course, a signal is not formally
regarded as occurring until Equations 5 and 6 also are
satis®ed. In real time, the formal signal cannot be recog-
nized for at least ®ve months after the occurrence of the
de®ned local minimum.
In order to reduce the possibility of false signals one
needs to add a caveat to the above signalling system, viz.
that a potential local minimum is disregarded if it is fol-
lowed by a local maximum within ®ve months. This is also
analogous to the Bry±Boschan algorithm. A local maxi-
mum at time t is de®ned as:
pij;t max p
>
p
p
…
;
2 ;. . . ;
‡
†
‡
1
‡
5
ij;t
ij;t
ij;t
and
(8)
A second component of the signal addresses the issue of
whether the transition probability is su ciently large and
whether it has been su ciently large for a su ciently long
enough period. After all, given the transition probability
may be expected to ¯ uctuate around the mean over time, it
does not seem sensible to use the mean as the sole signalling
criterion. Thus, it is also desirable to compare the prob-
ability in any current period with that observed in some
appropriate recent time period. This comparison is made
by monitoring the ratio of the current transition probabil-
ity to the most recent local minimum value and judge that
the probability has risen enough if the ratio exceeds two.
Although the threshold value of two seems to be somewhat
arbitrary, some alternative values were also tested, viz. 1.5,
3.0, etc., and 2 gives the best signal for turning points.
Thus, the two signal system proposed here consists of
two components as follows:
pij;t max p
>
p
p
…
;
ij;t¡2 ;. . . ;
†
ij;t¡1
ij;t¡5
Furthermore, a rule is required for determining if and
when a formal signal, having been given, should sub-
sequently be regarded as false. This would be the case if
a formal signal were given and a local maximum occurred
more than ®ve months later without a turning point being
in evidence before the occurrence of the next local mini-
mum. Finally, a turning point is regarded as missed if there
is no local minimum in evidence prior to the occurrence of
the turning point.
As an aside, it is recognized that, in general, Equation 8
represents a more natural de®nition of an extremum than is
Equation 7. However, the reason for adopting Equation 7
as the de®nition for a local minimum, rather than an ana-
logous version of Equation 8, is that Equation 7 results in
more frequent and more sensitive turning point signals
than Equation 8. It is also the case that one is only inter-
ested in monitoring for the required increases in the transi-
tion probability as described in the signalling system
represented by Equations 5 and 6.
-
1 p
:
p
5
>
… †
‡
ij;t0
s
ij
=
2 p
:
pij;t
2
6
… †
>
‡
s
ij;t0
0
-
where pij is the overall (long term) mean, t0 corresponds to
the most recent local minimum value of the relevant transi-
tion parameter, t0 ‡s expresses the time when the signal is
given, and s ¶ 5 (explained below).
IV. EMPIRICAL RESULTS
The time period, t0, is de®ned as the time at which the
relevant transition probability reached a local minimum.
The local minimum is formally de®ned as
Data
The analysis used monthly data on coincident composite
indexes (CC), short leading (LD), and/or long leading (LL)
pij;t
min p
…
p
p
2 ;. . . ;
ij;t0 r
7
… †
<
;
†
‡
1
‡
‡
ij;t0
ij;t0
0
7 As alternative rules, the mean plus one or two standard deviations were also considered. However, these alternatives were found to be
less successful in dating and predicting turning points.
8 See Bry and Boschan (1971).