Annette Prüss-Üstün and Sophie Bonjour

Public Health and Environment

World Health Organization (WHO)

Postal Address:20 avenue Appia, 1211 Geneva 27, Switzerland

Telephone:+41 22 791 3584 and +41 22 791 5419

Fax: +41 22 791 1383

E-mail: pruessa@who.int and bonjourso@who.int

Website: http://www.who.int/indoorair/mdg/en/

The percentage of population using solid fuels is the percentage of the population that relies on solid fuels as the primary source of domestic energy for cooking and heating. Solid fuels include biomass fuels, such as wood, charcoal, crops or other agricultural waste, dung, shrubs and straw, and coal.

This indicator is calculated as follows: The numerator is the number of people using solid fuels (in nationally representative sample) as the main cooking fuel, multiplied by 100. The denominator is the total population (in nationally representative sample).

Limitations of the indicator:

• The indicator uses solid fuel use as a proxy for indoor air pollution, as it is not currently possible to obtain nationally representative samples of indoor concentrations of criteria pollutants, such as small particles and carbon monoxide.
• The indicator is based on the main type of fuel used for cooking as cooking occupies the largest share of overall household energy needs. However, many households use more than one type of fuel for cooking and, depending on climatic and geographical conditions, heating with solid fuels can also be a contributor to indoor air pollution levels.

In principle, there is no discrepancy between global and national figures, as national data are not modified. However, values above 95% solid fuel use are reported as “>95%”, and values below 5% as “<5%” to avoid misinterpretation of the precision of the estimates.

Solid fuel use data are routinely collected at the national and sub national levels in most countries using censuses and surveys. Household surveys used include: United States Agency for International Development (USAID)-supported Demographic and Health Surveys (DHS); United Nations Children’s Fund (UNICEF)-supported Multiple Indicator Cluster Surveys (MICS); WHO-supported World Health Surveys (WHS); and other reliable and nationally representative country surveys.

The indicator draws on already published data sources and WHO therefore does not rely on country counterparts for obtaining data.

Until 2004, national data were not modified and reported as such. For the 2009 reporting (2007 being the year reported), as the number of nationally representative data has increased, the methods developed and implemented by the WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation (WHO & UNICEF 2006) were followed:

• Where solid fuel use information is available for a single year, a horizontal line is drawn six years into the past and six years into the future;
• Where solid fuel use information is available for two or more years that are spaced four or fewer years apart, an average is calculated. This average is extrapolated six years into the past and six years into the future.
• Where solid fuel use information is available for two or more years that are spaced at least five years apart, linear regression is performed. The linear regression line is extrapolated up to two years after the latest survey point and up to two years before the earliest survey point. Outside of these time limits, the extrapolated regression line is flat for four years in either direction. Where coverage reaches 0% or 100%, a horizontal line is drawn from the year before coverage reaches 0% or 100%.

Missing data are estimated based on the following criteria:

• All countries with a Gross National Income (GNI) per capita above USD 10,500 are assumed to have made a complete transition to using non-solid fuels as the primary source of domestic energy for cooking and heating.
• Missing data are not estimated for countries with a GNI per capita below USD 10,500, and for which no household solid fuel use data are available.

The indicator is currently reported for 186 countries with the number of countries for which data are obtained from nationally representative surveys increasing every year.

The population of interest includes the entire population of countries that have a relatively low national income (typically below USD 10,500).

The time lag between the reference year and actual availability of data series is often about 1-2 years, the time to analyze and publish the data.

The frequency of data production depends on the country; often, new data on use of solid fuels are only assessed once every few years.

Countries are population-weighted to obtain regional aggregates; for countries with no data, the regional mean exposure is assumed; for countries with less than 5% of solid fuel use (SFU), 0% is assumed for the calculation of regional or global means; for countries with more than 95% of SFU, 95% is assumed in the calculation of the mean.

Reporting of estimates by WHO is variable. Updates are produced approximately every two years and made available at: www.who.int/indoorair/mdg/en/.