About the food price index
The food price index (FPI) measures the rate of price change of a fixed basket of food goods and services purchased by households. The FPI aims to measure price changes of the same items (brand and relevant details) at each outlet over time. When there is a change in the size or quality of any of the goods or services in the basket, an adjustment is made to ensure that the price change shown in the FPI is not affected by the change in size or quality.
The FPI represents $16.9 billion spent on food by New Zealand households (at June 2011 month prices). This is based on information from the 2009/10 Household Economic Survey and other sources. This is equivalent to spending about $199 a week per household on food.
A full listing of the representative food items monitored in the FPI is available in Food price index review: 2011 (see tables 3 and 4).
Food prices are also included in the consumers price index (CPI). The food group is the only group of the CPI for which an index is prepared each month. The all groups CPI is prepared quarterly.
The sources and methods used to compile food prices are explained in Food prices in the consumers price index and food price index, available on the Statistics NZ website.
A price index measures the change in price between time periods for a given set of goods and services. It summarises a set of prices for a variety of goods and services collected from a number of outlets.
Grocery food specials: Items that are 'on special' or come 'off special' are included in the FPI at the price levels observed at the time prices are collected. An analysis of the price quotes for these items is often given for the meat, poultry, and fish; grocery food; and non-alcoholic beverages subgroups in the 'Commentary' section of this information release. To be included in this analysis, the priced item will have been on special either last month or this month, or have been on special in both months.
Upward/downward contributions: Items mentioned in this release are often those that made a large contribution to the overall movement in the FPI. An item's contribution is a combination of its weight in the index (ie its relative importance, based on its share of household spending on food) and the magnitude of price movement. For example, for two items recording the same percentage rise in price, the item with the larger weight in the FPI will have a larger contribution to the overall movement. This contribution is also referred to as points (or index points) contribution.