Life expectancy at age 1, infant mortality, and literacy are used as indicators of development, describing progress in health, sanitation, education, and women’s status. Gross National Product (GNP) is the standard measure of progress but does not show how output is distributed. The Physical Quality of Life Index (PQLI) is a summation of complex social interrelationships on which no theoretical explanation imposes any given weights/biases. Equal weight is assigned to each component.Source: Morris, MD (1980). "The Physical Quality of Life Index (PQLI).". Development digest 18 (1): 95 to 109.