The JMP uses household surveys and censuses

A few notable data sources are described here:

Demographic and Health Surveys (DHS)
Nationally-representative household surveys funded by the U.S. Agency for International Development (USAID) that provide data for a wide range of monitoring and impact evaluation indicators in the areas of population, health, and nutrition. Sample sizes range from 2,000 to 30,000 households, and surveys are conducted in over 75 countries approximately every 5 years. 

Multiple Indicator Cluster Surveys (MICS)
UNICEF assists countries in collecting and analyzing data in order to fill data gaps for monitoring the situation of children and women through its international household survey initiative the Multiple Indicator Cluster Surveys (MICS). Since the mid-1990s, the MICS has enabled many countries to produce statistically sound and internationally comparable estimates of a range of indicators in the areas of health (including water, sanitation and hygiene), education, child protection and HIV/AIDS.

World Health Surveys (WHS)
WHO has developed and implemented a Survey Programme and a World Health Survey to compile comprehensive baseline information on the health of populations and on the outcomes associated with the investment in health systems; baseline evidence on the way health systems are currently functioning; and, ability to monitor inputs, functions, and outcomes. Also within the implemented Survey Programme the WHO Evidence, Measurement and Analysis unit has developed the Study on global AGEing and adult health (SAGE) as part of an ongoing program of work to compile comprehensive longitudinal information on the health and well-being of adult populations and the ageing process.

Living Standards Measurement Surveys (LSMS) 
The Living Standards Measurement Study is an on-going research initiative of the World Bank generating policy-relevant household level data that provides an increasingly broad range of technical assistance as methods and technology continue to improve.

Population and housing censuses
Data on access to water and sanitation is often collected in housing censuses from most developing countries. They are therefore important sources of data for the JMP estimates. Current estimates are derived from over 250 censuses. 

This document provides international agencies and country statistics offices with questionnaire tools to arrive at data that is consistent for coordinated monitoring across countries.
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Learn more about the JMP method.