<prompt> Protein efficiency ratio is -Gain weight per unit of protein consumedProduct of digestibility coefficient and biological value divided by 100Percentage of nitrogen retained out of the nitrogen absorbedPercentage of protein absorbed after digestion  <response>: Protein efficiency ratio PER is based on the weight gain of a test subject divided by its intake of a paicular food protein during the test period. From 1919, until very recently, the PET has been a widely used method for evaluating the quality of protein in food Ref: Dictionary of public Health, Dr. Jugal Kishore Pgno : 423-424 