First, the food basket takes into consideration the habits prevailing in society. The way in which households assemble the calories they need varies from one country to another and, in higher-resource countries, households purchase more expensive calories. Non-food needs are not specified directly, but correspond to the spending ratio observed in households close to the poverty line. This ratio, known as the Orshansky ratio, tends to rise with income level, owing party to changes in relative prices (in developed countries non-tradable goods are more expensive) and partly changes in habits and tastes at higher levels of purchasing power.