Wednesday, March 25, 2009

The BBC need to find out what an index is

Oh dear me. The BBC need to find out what the difference between "an index" and "a change in an index" is.

Yesterday, their bulletins were routinely announcing that the Retail Price Index is at its "lowest ever".

Similarly, BBC Online stated:

But a sharp fall in mortgage repayments caused the Retail Prices Index (RPI), which includes housing costs, to fall to zero for the first time in 49 years.

Well, no actually. According to the Office for National Statistics, the Retail Prices Index is at 211.4. Far from zero.

What BBC Online should have stated is that "Retail Prices Index inflation" has fallen to zero for the first time in 49 years.

Similarly, those bulletins which hailed the "lowest Retail Prices Index ever" would have been more correct in saying that 'last month the Retail Prices Index was the lowest since the previous month'. What they meant to say, I think, is that 'the rate of change in the Retail Prices Index was the lowest ever'. But that is not so sexy is it?

The Office for National Statistics reported the situation correctly, as you would expect:

Retail Prices Index (RPI) inflation (my bolding) slowed to 0.0 per cent in February, down from 0.1 per cent in January

...RPI is the Retail Prices Index. The uses of the RPI and its derivatives include indexation of pensions, state benefits and index-linked gilts.


Inflation is the percentage change in the index compared with the same month one year previously.

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