JAMAevidence Glossary

Terms are derived from Users' Guides to the Medical Literature: A Manual for Evidence-Based Practice, 2nd Edition and The Rational Clinical Examination: Evidence-Based Clinical Diagnosis. Updated March 2010.
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Qualitative research
Qualitative research focuses on social and interpreted, rather than quantifiable, phenomena and aims to discover, interpret, and describe rather than to test and evaluate. Qualitative research makes inductive, descriptive inferences to theory concerning social experiences or settings, whereas quantitative research makes causal or correlational inferences to populations. Qualitative research is not a single method but a family of analytic approaches that rely on the description and interpretation of qualitative data. Specific methods include, for example, grounded theory, ethnography, phenomenology, case study, critical theory, and historiography.

Quality assurance
Any procedure, method, or philosophy for collecting, processing, or analyzing data that is aimed at maintaining or improving the appropriateness of health care services.

Quality improvement
An approach to defining, measuring, improving, and controlling practices to maintain or improve the appropriateness of health care services.

Quality of care
The extent to which health care meets technical and humanistic standards of optimal care.

Quality-adjusted life expectancy
The number of years of expected life corrected for the quality of life that patients are expected to experience in those years.

Quality-adjusted life-year
A unit of measure for survival that accounts for the effects of suboptimal health status and the resulting limitations in quality of life. For example, if a patient lives for 10 years and his or her quality of life is decreased by 50% because of chronic lung disease, survival would be equivalent to 5 quality-adjusted life-years. See also Cost-utility analysis.

Quantitative research
The investigation of phenomena that lend themselves to test well-specified hypotheses through precise measurement and quantification of predetermined variables that yield numbers suitable for statistical analysis.