Frank Strobel

English

Research Papers in Economics

Leaving EMU: a real options perspective
Frank Strobel
Dept. of Economics
Univ. of Birmingham
Birmingham B15 2TT, UK
Preliminary draft version: May 10, 2004
Abstract
We examine the real option implicit in a country’s decision of
whether to leave an existing monetary union when there is uncer-
tainty over the future beneﬁts of this move. Our theoretical model is
calibrated for the current Euro-12 area by proxying policymakers’ in-
ﬂation preferences with unemployment rates and debt-to-GDP ratios.
We observe a robust group of countries that would choose to remain
within EMU consisting of Belgium, Finland, Greece and Italy; France
and Spain loosely also belong to this core. Only Luxembourg would
robustly want to leave EMU; Ireland and the Netherlands, however,
complement that core closely.
Keywords: EMU; real option; calibration
JEL classiﬁcation:E 5 ,F 3
1 Introduction
The European Monetary Union (EMU) has only been in operation since 1
January 1999, yet some of the current member countries may already be
considering whether or not a return to monetary independence might be
1preferable. Policymakers are concerned about inﬂation performance, pos-
sibly because a time inconsistency problem in monetary policymaking can
cause an undesirable inﬂation bias to persist.1 If the future evolution of such
inﬂation preferences is uncertain, it may have a signiﬁcant impact on the
decision to leave the union because of policymakers’ reluctance to commit
to a largely irreversible move that might later prove less advantageous than
initially thought. This value of waiting, arising from the real options nature
of this problem, is well-known from the literature on irreversible investment
under uncertainty, can be substantial and needs to be properly accounted
for.2
Several papers have begun to address these issues. Strobel (in press), in
a two-country model where policymakers minimize loss functions over inﬂa-
tion and inﬂation preferences follow geometric Brownian motions, solves the
optimal stopping problem that describes a country’s decision of whether to
pursue monetary integration with the other one, and gives conditions under
which monetary integration can, or will never, be an equilibrium outcome.
More partial frameworks are used in Strobel (2001), which examines the value
of the option of monetary disintegration for a country in an existing mone-
tary union when inﬂation preferences follow a similar stochastic process, and
Strobel (2002), which extends the previous paper by deriving closed-form
solutions of the expected time and probability for a country in an existing
monetary union to want to return to monetary independence under such
circumstances.
Our present paper builds on and applies the theoretical model of Strobel
(in press) in examining the real option implicit in a country’s decision of
whether or not to leave a monetary union when the costs of later rejoining
it are considered prohibitively high and there is uncertainty over the future
beneﬁts of such a move. We show that a country perceives exercise of this
option of monetary disintegration as desirable only when the current value of
relative inﬂation preference parameters is larger than a speciﬁc trigger value;
intuitively, the lower a country’s inﬂation preference relative to the existing
1See e.g. Barro/Gordon (1983a,b).
2See e.g. Dixit/Pindyck (1994).
2union’s, the more it stands to gain from returning to monetary independence.
We then calibrate our theoretical model for the current Euro-12 area by prox-
ying policymakers’ inﬂa t i o np r e f e r e n c ep a r a m e t e r sw i t hb o t hu n e m p l o y m e n t
rates and debt-to-GDP ratios. Using annual data from OECD (2003), we
derive the proxied trigger values of relative inﬂation preference parameters
for time horizons of 50, 25 and 10 years to allow for diﬀering degrees of pol-
icymakers’ myopia and contrast them with the corresponding actual ratios
for 2002 and 2003 (predicted), our two reference periods.
Across the two proxies used, we observe a robust group of countries that
would choose to remain within EMU consisting of Belgium, Finland, Greece
and Italy; France and Spain generally also belong to this core but for the
10 year horizon using the debt-to-GDP ratio proxy. Luxembourg emerges
as the only country that would robustly want to leave EMU across both
proxies; Ireland and the Netherlands, however, complement that core except
for the 50 year horizon in the 2003 refer e n c ep e r i o du s i n gt h eu n e m p l o y m e n t
rate proxy. The cases for Austria, Germany and Portugal, by contrast, are
signiﬁcantly less clear cut, as their decisions of whether or not to exercise
the option of leaving EMU are seen to depend crucially on which particular
proxy and time horizon is used.
Section 2 now presents the model; the results of our calibration exercise
are reported in section 3, and section 4 concludes the paper.
2T h e m o d e l
The national and supranational policymakers’ objectives, for countries c and
the union u, entail the instantaneous loss rate
lit = πit
2 − ηit(πit − π
e
it) ,i = c,u (1)
where πit and πe
it are inﬂation and expected inﬂation, respectively.3
Policymakers’ inﬂation preference (or beneﬁt) parameters ηit ≥ 0 are
3This adapts the setup in Barro/Gordon (1983a); similar frameworks are used in Strobel
(2001, 2002, in press).
3assumed to follow geometric Brownian motions4
dηit = σiηitdzit (2)
where σi > 0 , dzit ∼ NID(0,dt) are increments of Wiener processes, and
Et(dzctdzut)=ρcudt with −1 < ρcu < 1 the coeﬃcient of correlation between
the processes zi .
We focus on a discretionary policy scenario under rational expectations
where policymakers solve for the optimal feedback rule π∗
i(ηi) that satisﬁes
t h el o s sf u n c t i o n
Lit =m i n
πi
Et
Z ∞
t
liτe
−µ(τ−t)dτ ,i = c,u (3)
with µ>0 the common discount rate, treating inﬂationary expectations πe
iτ
as given ∀τ ≥ t . We then obtain
Lemma 1 In a rational expectations equilibrium, the loss functions for the
national and supranational policymakers are
Lit =
1
4(µ − σ2
i)
ηit
2 ,i = c,u (4)
for µ − σ2
i > 0.
Proof. Analogous to the proof for Lemma 2 in Strobel (in press).
Ac o u n t r yc deciding on whether or not to leave the monetary union u
then solves the Bellman equation for the optimal stopping problem
F(Lu,L c)=m a x
½
Lu − Lc ,
1
µdt
Et[dF(Lu,L c)]
¾
(5)
where F(Lu,L c) is the value to country c of the option of leaving the monetary
union u ,a n dLu − Lc is the expected discounted beneﬁto fs u c ham o v e
when any other cost/beneﬁts are abstracted from.5 Note that this implicitly
4There is no consensus over whether inﬂation follows a non-stationary or a stationary
process, see e.g. Culver/Papell (1997), Lai (1997); a geometric Brownian motion is used
for analytical ease.
5We drop time subscripts for ease of notation.
4assumes that leaving a monetary union is an irreversible process, so that the
costs of possibly later rejoining it are considered prohibitively high. We can
then obtain
Proposition 2 Country c will want to exercise the option of leaving the
monetary union u if
ηu
ηc
> (
ηu
ηc
)
? =
s
2µ + σu
2 − 4ρcu σu σc + σc
2 + Θ
2(µ − σc
2)
where Θ =
p
(σu
2 − σc
2)2 +8 ( µ − ρcuσuσc)(σu
2 − 2ρcuσuσc + σc
2)
and not exercise it otherwise.
Proof. See Appendix.
Country c perceives exercise of the option to leave the monetary union
u as desirable only when the current value of relative inﬂation preference
parameters
ηu
ηc is greater than its trigger value (
ηu
ηc)? ; intuitively, the lower
ac o u n t r y ’ si n ﬂation preference relative to the union’s, the more it stands
to gain from returning to monetary independence. For the case where
ηu
ηc ≤
(
ηu
ηc)? , on the other hand, country c prefers to leave the option of monetary
disintegration unexercised and remains within the union for the time being.
3 A simple calibration
We proceed to calibrate the model in Section 2 for the current twelve mem-
bers of the Eurozone, proxying policymakers’ inﬂation preference (or beneﬁt)
parameters ηi with both unemployment rates and debt-to-GDP ratios. These
particular measures are chosen to reﬂect two widely cited rationales for the
potential beneﬁts of surprise inﬂation, as embodied in eq. (1), the expecta-
tional Phillips curve and governmental revenue motives.6
Using annual data from Annex Tables 14 and 33 in OECD (2003), we
calculate the required moments σi and ρcu from the respective transformed
6See e.g. Barro/Gordon (1983b) and Barro (1983), respectively.
5series ln( xt
xt−1) to allow for our distributional assumption of eq. (4). We then
compute the proxied trigger values of relative inﬂation preference parameters
(
ηu
ηc)? , from Proposition 2, for time horizons of 50, 25 and 10 years by apply-
ing discount rates µ of 3.5%, 5.4% and 11.3%, respectively.7 These results
a r ep r e s e n t e di nT a b l e s1a n d2 ,t o g e t h e rw i t ht h ep r o x i e dv a l u e sf o rt h er e l -
ative inﬂation preference parameters
ηu
ηc for 2002 and 2003 (predicted), our
two reference periods; in each case, we highlight in bold (italics) those values
consistent with country c’s exercise (non-exercise) of the option of leaving
the monetary union u , i.e. EMU, at all three time horizons.
For the unemployment rate proxy, we observe from Table 1 that a core
group of countries comprising Belgium, Finland, France, Germany, Greece,
Italy and Spain would prefer to remain within EMU irrespective of the time
horizon or reference period considered; this criterion provides a certain degree
of robustness. Portugal is also largely inclined to stay within EMU; it would
leave the union only for the 10 year horizon in the 2002 reference period.
The duo of Austria and Luxembourg, on the other hand, would choose to
exercise their options of leaving EMU for all time horizons and reference
periods, generating a second robust grouping. Ireland and the Netherlands
are also generally biased towards leaving EMU, except for the 50 year horizon
in the 2003 reference period where they would both stay put.
Results somewhat change when the debt-to-GDP ratio proxy is used. Ta-
ble 2 indicates that for this measure the robust group of countries preferring
to stay within EMU irrespective of time horizon or reference period now con-
sists of Belgium, Finland, Greece and Italy only. Austria, France and Spain
would also largely choose to remain within EMU in this case; only for the
10 year horizon would they exercise their respective options of leaving the
union. The opposing robust group of countries preferring to leave EMU for
all time horizons and reference periods, by contrast, now consists of Ireland,
Luxembourg and the Netherlands. In addition, Germany and Portugal would
also generally be inclined to leave EMU in this scenario, but for the 50 year
horizon where they would both stick to the status quo.
7Given our inﬁnite horizon framework, these approximate the application of a (real)
discount rate r of 2.5% over those ﬁnite time horizons T ,u s i n gµ = r
1−e−rT .
6St.dev. Corr. w/ u Trigger u/c Ratios u/c
50yrs 25yrs 10yrs 2002 2003(P)
Austria 0.07 0.64 1.29 1.22 1.15 1.54 1.47
Belgium 0.11 0.91 1.34 1.23 1.14 1.14 1.12
Finland 0.28 0.60 inf. inf. 2.68 0.90 0.95
France 0.07 0.93 1.12 1.09 1.06 0.93 0.94
Germany 0.10 0.89 1.30 1.21 1.13 1.06 1.06
Greece 0.07 0.49 1.35 1.26 1.17 0.82 0.92
Ireland 0.13 0.67 1.80 1.50 1.28 1.97 1.74
Italy 0.07 0.70 1.25 1.19 1.13 0.91 0.96
Luxembourg 0.13 0.89 1.65 1.40 1.22 2.79 2.22
Netherlands 0.15 0.76 2.23 1.66 1.33 3.34 2.13
Portugal 0.16 0.68 2.75 1.83 1.40 1.62 1.36
Spain 0.11 0.94 1.31 1.21 1.12 0.73 0.73
Euro area 0.08 1.00
Source: OECD (2003), Annex Table 14, Unemployment rates: commonly used definitions (per cent of labour force); 
           annual data 1986-2002; moments calculated from transformed series ln(x(t)/x(t-1)).  50/25/10 year time 
           horizons approximated by 3.5/5.4/11.3% discount rates. Bold/italic ratios indicate exercise/non-exercise at 
           all time horizons.
Table 1: Unemployment rate: triggers/ratios
Comparing our results across the two proxies used, we then observe a
robust group of countries that would choose to remain within EMU consisting
of Belgium, Finland, Greece and Italy; France and Spain generally also belong
to this core but for the 10 year horizon using the debt-to-GDP ratio proxy.
Luxembourg emerges as the only country that would robustly want to leave
EMU across both proxies; Ireland and the Netherlands, however, complement
that core except for the 50 year horizon in the 2003 reference period using the
unemployment rate proxy. The cases for Austria, Germany and Portugal, by
contrast, are signiﬁcantly less clear cut, as their decisions of whether or not
to exercise the option of leaving EMU are seen to depend crucially on which
particular proxy and time horizon is used.
4C o n c l u s i o n
We examined the real option implicit in a country’s decision of whether to
leave an existing monetary union when the costs of later rejoining it are
considered prohibitively high and there is uncertainty over the future ben-
7St.dev. Corr. w/ u Trigger u/c Ratios u/c
50yrs 25yrs 10yrs 2002 2003(P)
Austria 0.04 0.30 1.19 1.15 1.10 1.11 1.14
Belgium 0.03 0.63 1.11 1.09 1.06 0.71 0.74
Finland 0.19 0.49 inf. 2.68 1.66 1.59 1.66
France 0.05 0.81 1.15 1.12 1.08 1.12 1.09
Germany 0.06 0.71 1.20 1.15 1.10 1.20 1.17
Greece 0.08 0.48 1.38 1.28 1.17 0.72 0.74
Ireland 0.07 0.52 1.33 1.25 1.16 2.23 2.38
Italy 0.04 0.67 1.12 1.09 1.06 0.62 0.63
Luxembourg 0.10 0.72 1.55 1.38 1.23 13.01 13.85
Netherlands 0.04 0.67 1.14 1.11 1.07 1.42 1.45
Portugal 0.06 0.13 1.30 1.23 1.15 1.29 1.29
Spain 0.07 0.78 1.25 1.19 1.12 1.14 1.18
Euro area 0.03 1.00
Source: OECD (2003), Annex Table 33, General government gross financial liabilities (per cent of nominal GDP); 
           annual data 1985-2002 (except Ireland, Luxembourg 1990-2002); moments calculated from transformed 
           series ln(x(t)/x(t-1)). 50/25/10 year time horizons approximated by 3.5/5.4/11.3% discount rates. Bold/italic 
           ratios indicate exercise/non-exercise at all time horizons.
Table 2: Debt-to-GDP ratio: triggers/ratios
eﬁts of such a move. Our theoretical model was calibrated for the current
Euro-12 area by proxying policymakers’ inﬂation preferences with both un-
employment rates and debt-to-GDP ratios. Across the two proxies used, we
observed a robust group of countries that would choose to remain within
EMU consisting of Belgium, Finland, Greece and Italy; France and Spain
loosely also belonged to this core. Luxembourg emerged as the only country
that would robustly want to leave EMU across both proxies; Ireland and the
Netherlands, however, complemented that core closely. The cases for Aus-
tria, Germany and Portugal, by contrast, were signiﬁcantly less clear cut;
their decisions of whether or not to exercise the option of leaving EMU were
seen to depend crucially on the particular proxy and time horizon used.
Appendix
Proof. (Proposition 2) For country c , not leaving the monetary union u
f o raf u r t h e ri n s t a n tdt is optimal in the continuation region of the optimal
8stopping problem eq. (5), giving the relevant Bellman equation as
µF(Lu,L c)=
1
dt
Et[dF(Lu,L c)] (6)
Applying Ito’s Lemma to eq. (6) and noting that the value function F(Lu,L c)
should be homogeneous of degree 1,8 so that F(Lu,L c)=Lcf(Γ) where
Γ ≡ Lu
Lc ,9 we obtain
− f(Γ)
¡
µ − σc
2¢
+
¡
σu
2 − σc
2¢
Γf
0(Γ)
+2
¡
σu
2 − 2 ρcu σu σc + σc
2¢
Γ
2f
00(Γ)=0 (7)
as the diﬀerential equation that characterizes the evolution of f(Γ) in that
region.
We solve eq. (7) by standard methods, using the value-matching and
smooth-pasting conditions f(Γ∗)=Γ∗−1 and
∂f(Γ∗)
∂Γ =1, plus the boundary
condition f(0) = 0 ,10 and thus obtain
Γ
∗ =
γ1
γ1 − 1
where γ1 =
σu
2 − 4ρcu σu σc +3σc
2 + Θ
4( σu
2 − 2ρcu σu σc + σc
2)
> 1
and Θ =
p
(σu
2 − σc
2)2 +8 ( µ − ρcuσuσc)(σu
2 − 2ρcuσuσc + σc
2)
as the critical (trigger) value Γ∗. From the deﬁnition of Γ it then follows that
(
ηu
ηc
)
? =
s
2µ + σu
2 − 4ρcu σu σc + σc
2 + Θ
2(µ − σc
2)
i st h et r i g g e rv a l u eo fr e l a t i v ei n ﬂation preference parameters
ηu
ηc separating
the region in (ηu,ηc) space where country c’s option of monetary disintegra-
tion remains unexercised (i.e. for
ηu
ηc ≤ (
ηu
ηc)?) from the one where immediate
exercise of that option is perceived as optimal (i.e. for
ηu
ηc > (
ηu
ηc)?).
8This adopts the solution strategy in Dixit/Pindyck (1994, p. 210).
9Thus, Γ =
µ−σ2
c
µ−σ2
u
³
ηu
ηc
´2
from eq. (4).
10The geometric Brownian motion Γ has an absorbing barrier at zero.
9References
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[2] Barro, R.J. and D.B. Gordon, 1983a, Rules, discretion and reputation
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[3] Barro, R.J. and D.B. Gordon, 1983b, A positive theory of monetary
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[5] De Grauwe, P., 2003, Economics of monetary union, 5th. ed. (Oxford
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11

Leaving EMU: a real options perspective

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