The World Health Organization defines health as a "state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity." This section presents indicators of several important aspects or determinants of child health. Some of the indicators in this section relate to birth outcomes such as low birthweight, preterm birth, and infant mortality. Other indicators describe key health conditions, including emotional or behavioral difficulties, adolescent depression, obesity, and asthma. An indicator on the quality of children's diets compares children's dietary intake to recommended national dietary guidelines. The indicator on activity limitation presents a global measure that gauges the effect of chronic health conditions on children's functioning.