Unit of Analysis

In a statistical model, the unit of analysis is the entity about which inference is being made. For example, in a clinical study, an investigator must decide if inference is to be made with regard to individual patient outcomes or with regard to the physicians treating the patients. If the former, then the unit of analysis is the patient, and the resulting odds ratios or relative risks (or other statistics) would be interpreted as reflecting changes in patient risk or differences in patient characteristics. Similarly, it may be desirable to make inference regarding the treating physicians, each of whom may have treated multiple patients. In this case, statistical methods should be chosen so as to address questions related to the physician.

In most instances, the selection ...