FOI ref: FOI/2022/4636
You asked
I note that published inflation figures are usually 'rounded up' to one decimal point. However, I believe the Government use a more precise figure when calculating increases to benefits and pensions. I assume the ONS provide this information, although appearing to only publish the 'rounded' figure.
Would you please inform me of the CPI figure for September 2022, to greater than one decimal place?
We said
Thank you for your enquiry regarding the published inflation figures.
As part of the Consumer price inflation release, we publish the Consumer Prices Index (CPI) index values, and annual and monthly inflation rates. It is the annual inflation rates which are typically reported as the inflation figures.
Although the inflation rates are calculated to a higher level of precision, the National Statistics series is published to one decimal place within the statistical bulletin.
We follow a conventional approach to rounding rather than favouring rounding in one direction or the other. Our rounding policy and the effects of rounding are detailed in Section 10.4 of our Consumer Prices Indices Technical Manual, 2019.
In answer to your enquiry, the CPI annual inflation rate for September 2022 to four decimal places was 10.0951% and was published as 10.1%. Although an Official Statistic, the inflation rate to that level of precision would not be consider a National Statistic.
The CPI inflation rates are calculated following the standard approach, which is to calculate derived statistics from unrounded monthly indices. Where we publish the CPI index values to one and three decimal places (the latter are routinely published each month in Table 57 of the Consumer prices inflation tables), it is possible to calculate differing inflation rates from these differently rounded figures.
Since we calculate the published inflation rates from unrounded monthly indices, the published annual inflation rate could differ from the rate calculated from the indices published to one or three decimal places.
For September 2022, the annual inflation rate based on published index values rounded to one and three decimal places would have been 10.1423% (based on 112.4 and 123.8 for September 2021 and 2022) and 10.0956% (based on 112.415 and 123.764), respectively, to four decimal places.
Finally, I would like to reassure you that we do not provide inflation figures to other parts of the government to a greater level of precision that those published in or alongside the monthly Consumer price inflation release.