Coma Overview. A coma is a deep state of unconsciousness in which individuals do not consciously respond to stimuli in their environment. Coma can result from injury such as head trauma, or an underlying illness such as an infection or tumor, or toxins that enter the body. Patients in a coma are unable to think consciously and lack awareness of their surroundings, but they do retain basic life support functions, such as breathing and circulation.
The best known classification is that developed by the psychologist Stanley Smith Stevens, who proposed four levels, or scales, of measurement: nominal, ordinal, interval, and ratio.
System of measurement. A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce.