There are four main principles for organizing values of a nominal variable or a series of related health outcomes or other items. Alphabetical order, the order of items used on the original questionnaire or other data collection instrument, empirical order (ascending or descending numeric order), and theoretical groupings.

One principle to avoid is arbitrary order – whatever order you happen to recall the categories or items you seek or organize! The rest of this lecture will define and demonstrate each of these other principles and explain how to determine which one best fits the task at hand.