“Since 2010, our economy has grown by 15.8 per cent, meaning we can deliver world-class public services”

That’s what the Conservatives’ official Twitter account posted on Monday.

We’ve got thoughts.

UPDATE: The Conservative Party has finally got back to us with an explanation for their claims and said: 

“Our GDP calculation explained below

Q1 2010: 89.4
Q3 2017: 103.5

Percentage growth in GDP since Q1 2010 is 15.77 per cent.
(ONS, GDP index: seasonally adjusted, 25 October 2017)

“On public services, we are spending more on the NHS than ever before and this year the NHS has been ranked the best healthcare system of 11 wealthy countries by The Commonwealth Fund. The schools budget is also at a record level, and 1.8 million more pupils are in good or outstanding schools since 2010.”

Where does the 15.8 per cent figure come from?

There was no source provided in the tweet.

We’ve repeatedly asked the Conservatives where they’ve got this figure from, but they haven’t provided an answer. We’ll update this article if they do.

In the meantime, we put our thinking caps on to try and work out how they calculated the elusive “15.8 per cent”.

We looked at the difference between the total GDP of the UK economy in 2010 (£1.75 trillion) compared with 2016 (£1.92 trillion). But that’s a difference of 12.8 per cent – so we assume that’s not the source of the Tories’ claim.

Then we considered the change in GDP at “market prices” over the same period. That rose from £1.57 trillion to £1.92 trillion – a bump of 24.1 per cent. So again, probably not what they had in mind.

Then we wondered if they might have been adding together the annual GDP growth rates. It would be a strange technique, certainly… but even those figures were a way off the magic “15.8 per cent”.

As it stands, we can’t find a plausible explanation for the Conservatives’ claim that “since 2010, our economy has grown by 15.8 per cent”.

But even if the figures are correct, they’ve forgotten their record on public spending

The Conservatives’ tweet strongly suggests economic growth since 2010 has led to increased public spending. They said the boost means “we can deliver world-class public services”.

But in fact, since the party’s been in office, annual growth in government spending has consistently been lower than annual growth in GDP.

You can see this in the graph below, where areas shaded red show years in which spending growth has been weaker than GDP growth. (The purple areas show years when spending has grown faster than GDP).

The picture’s even more stark when we look at government spending as a proportion of GDP. Here we can see a sharp drop in spending (technically known as Total Managed Expenditure) from 2010.

Having peaked at nearly 46 per cent of GDP when the party first came to power, government spending is predicted to drop to around 36 per cent of GDP by the end of the decade.

It’s odd that a party that has spent much of its seven years in office implementing spending cuts would emphasise public services in this context.