To measure literacy using such a definition requires census or sample survey measurements under controlled conditions. In practice, many countries estimate the number of illiterate adults from self-reported data or from estimates of school completion. Life expectancy at birth is the number of years a newborn infant would live if prevailing patterns of mortality at the time of its birth were to stay the same throughout its life. Prevalence of child malnutrition is the percentage of children under 5 whose weight by age is less than minus two standard deviations from the median of the reference population. Access to sanitation is the percentage of the population with excreta disposal facilities that can effectively prevent human, animal, and insect contact with excreta.
Suitable facilities range from simple but protected pit latrines to flush toilets with sewerage.
To be effective, all facilities must be correctly constructed and properly maintained. In urban areas the source may be a public fountain or standpipe located not more than 200 meters away. In rural areas the definition implies that members of the household do not have to spend a disproportionate part of the day fetching water. The definition of safe water has changed over time. Adult illiteracy rate is the percentage of adults aged 15 and above who cannot, with understanding, read and write a short, simple statement about their everyday life.