There has recently been criticism of the Office for National Statistics’ retail sales growth rates as overly optimistic. However, the survey is the most comprehensive of its type, with the ONS claiming it covers around 95% of all retail sales in the UK. Accepting this robustness, this post looks at grocery retail sales data and considers the implications of omittances in calculating consumer prices inflation (CPI) for the real-terms growth rates (i.e. growth stripping out inflation) in retail sales.
CPI and retail sales figures
The ONS retail-sales survey collects data in current-value form and uses deflators derived from the official CPI figures to strip out the effects of inflation and so calculate real-terms growth. But there are questions over CPI and its possible over-statement of the inflation actually being felt by consumers, especially in food shopping. This would imply that the deflators used to calculate the real-terms retail-sales growth figures are too high. In turn, this suggests real-terms retail-sales growth is higher than that calculated by the ONS.
The figure below charts the official retail sales data recorded by the ONS in current prices, and calculated by the ONS in real terms.
Figure 1: Food retailers’ sales growth: annual % change, Jan – Nov 2011

Source: ONS
The accuracy of CPI in grocery
The particular problems of applying CPI to grocery retailing include:
- the exclusion of multibuy offers (BOGOFs, 3-for-2s etc) from CPI calculations – although CPI does take into account straight discounting (half-price etc).
- the exclusion of coupons which are helping to suppress the amount consumers are paying in cash: e.g. Asda’s £5 off a subsequent £40 shop, online voucher codes, and manufacturer coupons.
- the exclusion from CPI calculations of loyalty-card redemption points/vouchers as a further means of decreasing the amount consumers are paying in cash.
These exclusions are significant – in July 2011 Nielsen estimated 39% of grocery spending was on promoted goods. Although any straight discounting will be factored into CPI, any multibuy or other irregular offers will not, so consumers taking advantage of the numerous 2-for-1s, for example, do not register. Consequently, consumers are not feeling grocery inflation anywhere near the 4.6% grocery deflator figure given by the ONS (at November 2011).
In July 2011, Waitrose MD Mark price claimed that same-product food inflation was running at around 3% year-on-year, and with consumers downtrading the rate being felt by customers was more like 2.1%. At that time, the deflator being used for food retail figures by the ONS was 5.9%. If we extrapolate the ratios between these two figures (3% and 5.9%) across 2011, we get an alternative “Waitrose-derived” deflator, charted below; this is simplistic but suggestive of a potential alternative real inflation rate in food retailing.
Figure 2: ONS deflator and alternative deflator for food retailers’ retail sales, Jan – Nov 2011

Source: ONS/public domain
Applying the alternative deflator to retail sales data
Applying this alternative grocery-prices deflator to the current-prices food retail sales growth published by the ONS produces an alternative set of real-terms data. Is this actually closer to the real growth rates being seen in food retailing?
Figure 3: Food retailers’ sales growth: annual % change, Jan – Nov 2011

Source: ONS/public domain