The ‘secret deflator’ used to fiddle the GDP figures

Rather than use the RPI to calculate GDP, the government uses its own ‘secret deflator’. And that gives a completely different view of the economy.

I wrote here a few weeks ago about the oddly opaque manner in which the government figures out what inflation-adjusted GDP growth in the UK is.

It doesn't use the RPI or the CPI as a representative of inflation - as you might think they would instead, it uses its own deflator. I have no idea how that is calculated, and I strongly suspect that almost no one else does either.

The key point to note is that until 2010 the RPI and the deflator were much of a muchness. But in the last few years, they have suddenly (and to my mind inexplicably) parted ways.

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James Ferguson at MacroStrategy Partners has kindly picked this point up for me and produced this chart:

Real GDP vs NGDP adjusted for RPI

13-07-25-GDP-v-NGDP

If you assume that the Office for National Statistics' occult calculations for the deflator are entirely reasonable and correct, the UK has avoided a double dip recession (hooray!).

If, on the other hand, you note that the deflator and the RPI have rarely diverged in the past, and so think that using the RPI to deflate nominal GDP continues to make perfect sense, it turns out that the real economy has been contracting since 2008 (boo!).

That's not a double dip. It is a depression.

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Merryn Somerset Webb

Merryn Somerset Webb started her career in Tokyo at public broadcaster NHK before becoming a Japanese equity broker at what was then Warburgs. She went on to work at SBC and UBS without moving from her desk in Kamiyacho (it was the age of mergers).

After five years in Japan she returned to work in the UK at Paribas. This soon became BNP Paribas. Again, no desk move was required. On leaving the City, Merryn helped The Week magazine with its City pages before becoming the launch editor of MoneyWeek in 2000 and taking on columns first in the Sunday Times and then in 2009 in the Financial Times

Twenty years on, MoneyWeek is the best-selling financial magazine in the UK. Merryn was its Editor in Chief until 2022. She is now a senior columnist at Bloomberg and host of the Merryn Talks Money podcast -  but still writes for Moneyweek monthly. 

Merryn is also is a non executive director of two investment trusts – BlackRock Throgmorton, and the Murray Income Investment Trust.