A property or attribute of a material that is measured, compared or noted. Attributes are ordinarily qualitative characteristics, but quantitative characteristics (variables) may be converted into attributes by assigning items to certain categories on the basis of the measured values. The value of the characteristic determined as a result of an observation or test is the observed value; when determined by a specified test method, it is called the test result. The concentration or quantity of an analyte as estimated by use of a sample is usually the characteristic of interest in analytical chemistry.