QOL: Acronym for quality of life.

Quality-adjusted life-years: An adjustment of life expectancy that reduces the overall expectancy by amounts that reflect the existence of chronic conditions causing impairment, disability and handicap as assessed from health survey data. Useful in economic analyses as a measure of health outcomes that reflects both lives saved and patient's valuation of quality of life in alternative states. [Quality of Life Research, 2002, 11, 37–45.]

Quality-adjusted survival analysis: A methodology for evaluating the effects of treatment and other covariates on survival times that allows consideration of both quality and quantity of life. [Annals of Hematology, 2005, 84, 47–55.]

Quality-adjusted survival times: The weighted sum of different time episodes making up a patient's survival time, with the weights reflecting the quality of life of each period. [Statistics in Medicine, 1993, 12, 975–88.]

Quality assurance: Any procedure or method for collecting, processing or analysing data that is aimed at maintaining or improving the reliability or validity of the data.

Quality control procedures: Statistical procedures designed to ensure that the precision and accuracy of, for example, a laboratory test are maintained within acceptable limits. The simplest such procedure involves a chart (usually called a control chart) with three horizontal lines, one drawn at the target level of the relevant control statistic, and the others, called action lines, drawn at some prespecified distance above and below the target level.