The endless debate about the relative merits of Quantitative research and Qualitative research remains a central theme in evaluating evidence to guide nursing practice. Yet, this dichotomy is at best a misnomer and at worst an obfuscation of real issues.

Quantitative and qualitative refer to data: counted or numeric and narrative or categorical. Quantitative data arise from measurement processes that assign numerical values indicating greater or lesser amounts that can be analyzed in prescribed ways. Qualitative data arise from words describing values of things that are not meaningful as varying amounts (gender, experiences, occurrences, and actions). These qualitative data may be analyzed by counting or with procedures that produce themes or patterns representing unique experiences of individuals or groups.

Analyzing evidence for application in practice focuses on the likelihood that (a) the phenomenon addressed in the research project will occur in the future in similar or dissimilar settings and (b) the relationships found between the actions and events are causal and not coincidental. The first represents generalizability of knowledge (external validity), and the second refers to the certainty of relationships found among study concepts (internal validity).

Experimental studies (e.g., randomized controlled trials) use qualitative as well as quantitative data. The intervention (treat/not treat) is qualitative-the event of treatment occurred or did not. The outcome could be a change in the subjects' condition, death or life, another qualitative indicator. Much more important to evaluating evidence for practice than the qualitative-quantitative data issue is whether the intervention rather than some other event brought about the observed effect and whether this intervention would have the same result in the future, in other settings, with other patients.

Exploratory studies, with no intention of showing causal relationships, use both quantitative and qualitative data. Measurement procedures assign greater or lesser values to phenomena and then analyze to determine clustering, associations between phenomena, and differences across groups or time. These studies use advanced statistical procedures with intricately measured quantitative data, but they are not intended to create interventions for practice. To the extent that exploratory studies correctly describe an objective phenomenon that will likely exist in other populations and settings (general knowledge), the information can help us understand problems and inform practice. Exploratory studies that interpret unique phenomenon not likely to occur in other persons at other times and places are interesting but cannot guide practice interventions. To be applied in practice, knowledge must inform decisions about the likely effect of a selected action (treatment decision, care process, and management decision) on an outcome of interest.

The qualitative-quantitative debate must be re-framed to promote clarity of language and of thought. Persons in training to conduct or apply research must understand the basis for making judgments about the strength of the evidence. It is not about qualitative or quantitative data, but whether the evidence was produced using procedures that promote certainty about the relationships and confidence that the knowledge will apply to groups whose care we wish to improve.

Mary A. Blegen, PhD, RN, FAAN

Professor and Director of the Center for Patient Safety

School of Nursing, University of California San Francisco