Final answer:
The criterion used to indicate malnourishment in children under age five is mid-upper arm circumference (MUAC). MUAC is a measurement of the circumference of the upper arm and is used as a simple and reliable indicator of nutritional status in children.
Step-by-step explanation:
The criterion used to indicate malnourishment in children under age five is mid-upper arm circumference (MUAC).
MUAC is a measurement of the circumference of the upper arm and is used as a simple and reliable indicator of nutritional status in children. A smaller MUAC measurement can suggest malnutrition and the need for intervention.
Other criteria such as body mass index (BMI), height-to-weight ratio, and waist circumference are not specifically used to indicate malnourishment in children under age five.