The World Health Organization defines health as a "state of complete physical, mental, and social wellbeing, and not merely the absence of disease or infirmity." This section presents indicators of several important determinants of child health. Some of the indicators in this section relate to birth outcomes such as low birthweight and infant mortality. Other indicators describe key health conditions, including emotional or behavioral difficulties, overweight, and asthma. The indicator on activity limitation presents a global measure that gauges the effect of chronic health conditions on children's functioning.