<Li> The ideal, rarely realisable in practice, would consist of estimates of expenditure for each detailed consumption category, for each type of outlet, for each region . </Li> <Li> At the opposite extreme, with no regional data on expenditure totals but only on population (e.g. 24% in the Northern region) and only national estimates for the shares of different outlet types for broad categories of consumption (e.g. 70% of food sold in supermarkets) the weight for sliced bread sold in supermarkets in the Northern region has to be estimated as the share of sliced bread in total consumption × 0.24 × 0.7 . </Li> <P> The situation in most countries comes somewhere between these two extremes . The point is to make the best use of whatever data are available . </P> <P> No firm rules can be suggested on this issue for the simple reason that the available statistical sources differ between countries . However, all countries conduct periodical household - expenditure surveys and all produce breakdowns of consumption expenditure in their national accounts . The expenditure classifications used there may however be different . In particular: </P>

Consumer price index falls in the category of