In order to carry out this calculation, the indigence line is multiplied by a factor that differs for urban and rural areas. For poverty estimates up until 2006, a factor of 2 was used for urban zones and a factor of 1.75 was used for rural areas.aThe factors applied since 2007 vary depending on the differentials between trends in the prices for foodstuffs and for other goods and services. Since 2007, the indigence line is updated on the basis of the CPI for food products, while the portion of the poverty line corresponding to expenditure on non-food goods is updated using the non-food CPI. In line with standard ECLAC practice, the data have been corrected to account for the non-response rate for some income-related questions from wage earners, the self-employed and retirees and to mitigate probable underreporting biases. This latter operation is carried out by comparing the responses to income-related questions in the survey with estimates based on the household income and expenditure accounts included in each country's application of the System of National Accounts. These estimates are calculated using official information.