How much does it hurt? Pain is a psychological state that can be difficult to measure. One way to put a number on a pain is to have people judge with reference to the external expression of the internal state.

FACES FROM HOCKENBERRY MJ, WILSON D: WONG’S ESSENTIALS OF PEDIATRIC NURSING, ED. 8, ST. LOUIS, 2009, MOSBY. USED WITH PERMISSION. COPYRIGHT MOSBY.