Why good news for GDP isn't necessarily good news for the Chancellor

The output gap is a strange and unpredictable beast, writes Nida Broughton.

The Coalition came into Government in 2010 with a plan to repair the public finances and set itself a target to eliminate the structural deficit. The ONS today published figures showing that GDP in the second quarter of this year is even higher than we thought, rising by 0.7 per cent rather than 0.6 per cent. But it isn’t clear if this is good or bad news for the Chancellor’s deficit strategy, because the structural deficit – and therefore the billions of cuts that George Osborne is pencilling in – is determined by small changes in a very slippery measure of the state of the economy: the output gap.

The Government’s structural deficit target is carefully worded to take into account the fact that part of the deficit – the “cyclical” part – will automatically disappear as the economy recovers. From a theoretical point of view, this makes sense: there is little point on focusing efforts on areas of spending that are going to fall anyway. The non-cyclical, “structural” part of the deficit – the part that will remain even when the economy is back on track is surely the part to be concerned about. 

So since 2010, the Office for Budget Responsibility (OBR), whose remit is to report on Government’s performance against its fiscal targets, has set about trying to measure the “output gap” – a measure of how far the economy has to recover.  The output gap is the difference between actual GDP and “potential” GDP. Potential GDP is the level of GDP that the economy could achieve if it were operating at “full capacity”.

But it has become increasingly clear that in practice, the output gap is just too difficult to measure. The OBR’s twice-yearly reports always show a comparison of the OBR’s estimate of the output gap against those made by other forecasters – including banks and independent forecasting houses. This provides a useful sense-check of the OBR’s figures. 

The last OBR report in March, showed, as it always has done, the huge range that different forecasters have come up with in measuring the output gap – ranging from -7.3 per cent to -0.9 per cent for 2013. To put this into context, just a two percentage point difference in the output gap estimate is enough to change the forecast structural deficit in the Government’s target year of 2018 by around £28bn – no small amount when the Government is looking to cut around £33bn after the election.

Earlier this month, the Bank of England, searching for a way to measure the state of the economy as part of its Forward Guidance, decided against the output gap, saying that:

“The output gap is unobservable and difficult to explain, and any estimate would be subject to substantial uncertainty.”

Instead, it plumped for unemployment as a measure. And now even as the economy is showing some signs of life, independent forecasters still can’t agree among themselves on what the positive growth figures mean for the output gap, as shown in the chart below. Of those releasing estimates after July’s surprise good news on growth from the ONS, two thought this meant the economy was now closer to potential. One thought that it was now further away – presumably taking the good news on GDP to be a sign of underlying productivity improvements that mean that the economy’s potential has expanded. And two kept their output gap estimate unchanged. 

Chart: Forecasts of the output gap in 2013

HM Treasury, Forecasts for the UK economy: a comparison of independent forecasts, August 2013

The question has to be asked: how useful is a public spending target that depends on such an uncertain measure of the economy? Perhaps recognising this, or perhaps because it made for a better statistic, George Osborne omitted to mention the “structural deficit” at all in his last Spending Review speech in June, referring instead to the overall deficit. And even though the structural deficit – on OBR forecasts - is due to go into surplus by 2016-17, George Osborne’s planned cuts stretch out to 2018. So does the Chancellor himself still believe in the usefulness of his target?

The Chancellor. Photograph: Getty Images

Nida Broughton is Senior Economist at the Social Market Foundation.

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Inside Big Ben: why the world’s most famous clock will soon lose its bong

Every now and then, even the most famous of clocks need a bit of care.

London is soon going to lose one of its most familiar sounds when the world-famous Big Ben falls silent for repairs. The “bonging” chimes that have marked the passing of time for Londoners since 1859 will fall silent for months beginning in 2017 as part of a three-year £29m conservation project.

Of course, “Big Ben” is the nickname of the Great Bell and the bell itself is not in bad shape – even though it does have a huge crack in it.

The bell weighs nearly 14 tonnes and it cracked in 1859 when it was first bonged with a hammer that was way too heavy.

The crack was never repaired. Instead the bell was rotated one eighth of a turn and a lighter (200kg) hammer was installed. The cracked bell has a characteristic sound which we have all grown to love.

Big Ben strikes. UK Parliament.

Instead, it is the Elizabeth Tower (1859) and the clock mechanism (1854), designed by Denison and Airy, that need attention.

Any building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster.

Repairs to the tower are long overdue. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. There is water damage to the masonry and condensation problems will be addressed, too. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting.

Marvel of engineering

The clock mechanism itself is remarkable. In its 162-year history it has only had one major breakdown. In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. The resulting damage took months to repair.

The weights that drive the clock are, like the bells and hammers, unimaginably huge. The “drive train” that keeps the pendulum swinging and that turns the hands is driven by a weight of about 100kg. Two other weights that ring the bells are each over a tonne. If any of these weights falls out of control (as in the 1976 incident), they could do a lot of damage.

The pendulum suspension spring is especially critical because it holds up the huge pendulum bob which weighs 321kg. The swinging pendulum releases the “escapement” every two seconds which then turns the hands on the clock’s four faces. If you look very closely, you will see that the minute hand doesn’t move smoothly but it sits still most of the time, only moving on each tick by 1.5cm.

The pendulum swings back and forth 21,600 times a day. That’s nearly 8m times a year, bending the pendulum spring. Like any metal, it has the potential to suffer from fatigue. The pendulum needs to be lifted out of the clock so that the spring can be closely inspected.

The clock derives its remarkable accuracy in part from the temperature compensation which is built into the construction of the pendulum. This was yet another of John Harrison’s genius ideas (you probably know him from longitude fame). He came up with the solution of using metals of differing temperature expansion coefficient so that the pendulum doesn’t change in length as the temperature changes with the seasons.

In the Westminster clock, the pendulum shaft is made of concentric tubes of steel and zinc. A similar construction is described for the clock in Trinity College Cambridge and near perfect temperature compensation can be achieved. But zinc is a ductile metal and the tube deforms with time under the heavy load of the 321kg pendulum bob. This “creeping” will cause the temperature compensation to jam up and become less effective.

So stopping the clock will also be a good opportunity to dismantle the pendulum completely and to check that the zinc tube is sliding freely. This in itself is a few days' work.

What makes it tick

But the truly clever bit of this clock is the escapement. All clocks have one - it’s what makes the clock tick, quite literally. Denison developed his new gravity escapement especially for the Westminster clock. It decouples the driving force of the falling weight from the periodic force that maintains the motion of the pendulum. To this day, the best tower clocks in England use the gravity escapement leading to remarkable accuracy – better even than that of your quartz crystal wrist watch.

In Denison’s gravity escapement, the “tick” is the impact of the “legs” of the escapement colliding with hardened steel seats. Each collision causes microscopic damage which, accumulated over millions of collisions per year, causes wear and tear affecting the accuracy of the clock. It is impossible to inspect the escapement without stopping the clock. Part of the maintenance proposed during this stoppage is a thorough overhaul of the escapement and the other workings of the clock.

The Westminster clock is a remarkable icon for London and for England. For more than 150 years it has reminded us of each hour, tirelessly. That’s what I love about clocks – they seem to carry on without a fuss. But every now and then even the most famous of clocks need a bit of care. After this period of pampering, “Big Ben” ought to be set for another 100 or so years of trouble-free running.

The Conversation

Hugh Hunt is a Reader in Engineering Dynamics and Vibration at the University of Cambridge.

This article was originally published on The Conversation. Read the original article.