1. Introduction

The consumer price index (CPI) and the European harmonised index of consumer prices (HICP) measure monthly price developments for goods and services purchased by consumers. The inflation rate is based on the year-on-year change in the CPI. Energy includes ECOICOP groups 4.5.1 (electricity), 4.5.2 (natural gas) and 4.5.5 (district heating). In 2022, electricity and natural gas accounted for 2.6% and 3.0% of the CPI, respectively. District heating will not be discussed here.

Up to the reporting month of May 2023, pricing data was obtained from the Netherlands Authority for Consumers and Markets (ACM) every month to calculate the CPI for energy.  The data in question was collected through monthly sample surveys of only newly concluded energy contracts. For a long time, this method provided a good picture of price trends in the energy market. Moreover, it was implicitly approved by Eurostat, the statistical office of the European Union, as shown by the organisation’s annual report for 2021: in the section on compliance monitoring, energy is not identified as an area of concern (2023). ACM’s data collection was efficient and, in accordance with government guidelines, no duplicate information requests were submitted.

However, with the large price increases for energy products from mid-2021, the price development of new contracts was less representative of the broader market, as about half of all consumers had long-term, fixed-rate contracts when the price hikes started. In addition, many consumers with existing older, variable-rate contracts paid lower rates than consumers with new contracts. As the method described above does not provide a complete picture of all transactions in a volatile market, additional data was sought. A number of energy companies agreed to submit overviews of consumer contract data to Statistics Netherlands (CBS). This data provides comprehensive insight into the rates paid by all customers of the companies concerned, which has significantly broadened CBS’s view of price trends in the energy market.

The availability of these new data sources has also made it possible to apply new methods specifically designed for detailed data. CBS started using these methods in the reporting month of June 2023. The same methodology is used for the CPI and the HICP. Below, references to the CPI include the HICP.
The purpose of this report is to explain the methodology used. Some results of the research that was conducted to arrive at this methodology are discussed as well. This report is structured as follows: Chapter 2 describes the new data, Chapter 3 explains the new methodology, and figures presenting outcomes have been included in the annex (Chapter 5).