Government statisticians began visiting homes over the weekend for the start of the 2004 expenditure survey.

Around 1,200 households will be targeted during May and June to gather information to update how the consumer price inflation index is measured.

It was last updated in 1993 but people are now buying new types of goods and services and so the market basket must be updated to reflect new spending patterns.

The survey is compulsory and is done under the authority of the Statistics Act but interviewers will leave leaflets to help answer some of the questions householders might have.