Counts, scales, and scores. Levels of observation

Description, analysis, and interpretation of biomedical information are guided, in part, by the nature of the observations. Objects or events in categories, ie, nominal data, are simply counted. At a somewhat higher level, observations may have a "more than" character, so they can be ordered or ranked; the increments between the elements may be unknown or not measurable. Interval data have known and fixed increments, but no true zero; ratio scales are interval observations with a true zero. Some relationships between the levels of observation and the presentation and interpretation of biomedical information are discussed.