Definition and Criteria for Classification. Certain questions are important and should be asked early in classification development: At an abstract level, what is to be classified? How does a concept (notion) become a diagnosis, accepted for classification?

The NANDA definition of a nursing diagnosis was accepted by the NANDA membership in 1988; it is adapted from a national, Delphi study by Dr. Joyce Shoemaker (1984):

Nursing diagnosis is a clinical judgment about individual, family, or community responses to actual or potential health problems/life processes. Nursing diagnoses provide the basis for selection of nursing interventions to achieve outcomes for which the nurse is accountable (North American Nursing Diagnosis Association, 1997).

Because the focus of nursing diagnosis is abstract, this definition is acceptable to nurses of different theoretical persuasions and colleagues in other professions. In nursing it is challenged by some because of the implications for the scope of nursing diagnosis. A discussion of this controversy over the last sentence is better left to a discussion of issues below.

A diagnostic concept, or category, is formed from a set of empirical indicators (signs/symptoms) observed together frequently enough to capture nurses' attention. The set of indicators is given a name and definition. Ideally, as in other professions, clinicians would report their observations in a journal to alert others to the phenomena. Further observation leads to identification of contributing factors which will be the focus of nursing intervention. Qualitative studies using grounded theory or other methods, should follow. Quantitative research methods are useful when there is a tentative formulation of the concept and contributing factors or when the category is ready for epidemiological studies. Norris (1982) has offered methods of concept clarification and Gordon (1990) has proposed a cycle of development for determining the conceptual base of a diagnostic category.

Recent work in cognitive theory suggests ways of looking at concepts that will be useful for studies of the developmental, cultural, gender, and illness-related variables which influence defining characteristics of a diagnostic concept. Research and development in this area has to be informed by the research on human cognitive architecture, concept learning, and diagnostic reasoning (Rosch and Lloyd, 1990; Van Mechelen, Hampton, Michalski, and Theuns, 1993; Gordon, 1994).

Research on the validity and reliability of diagnostic categories has increased considerably in the last decade but is still insufficient. This is a serious problem. Diagnostic reasoning and judgment require valid and reliable diagnostic concepts that facilitate, rather than inhibit, thinking. Large scale funding for the basic research that is needed to identify, develop, and validate diagnostic categories has not been available in grants or contracts in the USA or Canada. In contrast, in other regions of the world large scale validation projects have been funded (Mortensen, 1996). Although nursing diagnosis always has been one of the standards for professional practice (American Nurses Association, 1973) and part of the profession's contract with society (American Nurses Association, 1980; Canadian Nurses Association, 1993) leaders in nursing research have not always supported the need for a language and classification system that differs from medicine.