Of all the more intractable problems I have encountered,
Brexit is top of the list. Every time we think we have found a way forward,
reality intervenes to cast us back to square one. It strikes me that one reason
for this is that we are thinking about the problem in a binary way, which is
inappropriate given the complexity of the issue. As it is conventionally
presented in the media – and indeed in parliament – Brexit is a simple case of
in or out. The prime minister’s ill-judged attack on MPs last week was a product of this kind of simplistic thinking. But it is wrong. There is a
cost associated with each choice and the optimal strategy is to choose the one
with the lowest costs. It is thus wrong to think simply of “in” or “out.” The
real choice has always ever been between “in” and “what kind of out?”
Rather than trying to solve the problem by looking forward,
we can use the method of backward induction which begins by looking at the end
point and working back to determine the path necessary to get there. One of the
great advantages of this approach is that it allows us to abstract from a lot
of the political noise surrounding the current debate. Thus, to answer the
question of how to leave the EU with an agreement that minimises economic costs
to the UK, we can work out the sequence of events designed to get us to that
point. By sequentially going through the outcomes, we end up gradually
eliminating all the impossible options until only the possible ones remain.
None of them accord with the plans put forward by the most fervent Brexit
supporters.
But whilst this is an approach which allows us to look at
desired outcomes, methods of voter choice help us to assess how we actually
arrive at our choices, however unlikely they may be. Consider a system of
single transferable votes in which 650 MPs face four options, A, B, C and D.
Suppose they rank their preferences from 1 to 4. If no option commands a
majority, the lowest-ranked first choice is eliminated from the ballot and the
remainder are subject to a vote in the next round. The attached chart shows the
sequence of how this might pan out.
In the first round, options A and D have an equally low
number of first preferences but A is eliminated because it has a smaller number
of second preferences. In the second round, D again scrapes through on the
basis of having more second round votes than C and in the final round it ends
up on top because more voters switched their allegiance to D than B, despite
the fact that D was never a first choice winner in either of the first two
rounds. Imagine now that option D is either a hard Brexit or revocation of
Article 50. Although these are not plausible outcomes today, such a voting
system demonstrates how they could end up as being the favoured choice
depending what other choices are available.
An alternative voting system is the Condorcet method which attempts to force a decision by holding a series of one-on-one votes to
determine whether there is one preference that comes out on top. In our
example, we thus run six votes (A vs B); (A vs C); (A vs D); (B vs C); (B vs D)
and (C vs D). If preferences are transitive (i.e. if A is preferred to B and B
is preferred to C, then A must be preferred to C), it is possible to derive a
winner. But if they are non-transitive it is not. Imagine, for example, the
case where MPs are asked to choose between accepting the Withdrawal Agreement
and revoking Article 50 and opt for the former. In a second vote, MPs prefer
accepting the Withdrawal Agreement over a hard Brexit but in a third vote they
express a preference for a hard Brexit over revoking Article 50. It is thus
impossible to derive a series of ordinal preferences. This is known as the
Condorcet paradox which we can liken to the game rock-paper-scissors, to which
there is no obvious solution.
The work of Nobel Laureate Kenneth Arrow highlighted the
problems involved in arriving at optimal choices. He gave his name to Arrow’s impossibility theorem which suggests that when there are three or more options, no ranked voting
system can convert the ranked preferences of each individual into an overall
ranking which meets a number of specific criteria. Perhaps the most important
of these is that one person or group of people cannot be made better off
without making others worse off (the Pareto criterion). This is an accurate
description of where we are in the Brexit debate given the sentiments expressed
on the streets of London at the weekend.
Continuing to put a series of votes to parliament, none of
which commands a majority, can ever be guaranteed to find a resolution to the
Brexit problem. The very fact that the electoral split in favour of leaving the
EU was not much more than 50-50 ought to make us question why MPs can find a
resolution when the electorate could not find a solution to the Brexit
impossibility conundrum. The government’s approach has been to treat the
outcome as a zero-sum game. But as the estimated one million people marching
through London at the weekend highlighted, this approach is far from
satisfactory. The only resolution to the problem is to buy more time: Kick the
can down the road in the hope that society is able to agree on an acceptable
compromise. Theresa May gained only an additional three weeks. It’s not enough!