QUADAS Quality Assessment of studies of Diagnostic Accuracy included in Systematic reviews. An evidence-based quality assessment tool to be used in systematic reviews of diagnostic accuracy studies. The checklist includes items that cover patient spectrum, reference standard, disease progression bias, verification bias, review bias, clinical review bias, incorporation bias, test execution, study withdrawals, and indeterminate results. It is presented together with guidelines for scoring each of the items included in the tool.327 See also consort; quorum; stard; strobe; trend.

QALYs See quality-adjusted life years.


  1. Observations or information characterized by measurement on a categorical scale, i.e., a dichotomous or nominal scale, or, if the categories are ordered, an ordinal scale. Examples are sex, hair color, death or survival, and nationality. See also measurement scale.
  2. Systematic nonnumerical observations by sociologists, anthropologists, etc., using approved methods such as participant observation or key informants. Qualitative data can enrich understanding of complex problems and help to explain why things happen.

QUALITATIVE RESEARCH Any type of research that employs nonnumeric information to explore individual or group characteristics, producing findings not arrived at by statistical procedures or other quantitative means. Examples include clinical case studies, narrative studies of behavior, ethnography, and organizational or social studies.328

QUALITY-ADJUSTED LIFE EXPECTANCY (QALE) A model for clinical decision making in which estimates of impairment or disability are included in the calculation of life expectancy.

QUALITY-ADJUSTED LIFE YEARS (QALYs) An adjustment of life expectancy that reduces the overall life expectancy by amounts that reflect the existence of chronic conditions causing impairment, disability, and/or handicap as assessed from health survey data, hospital discharge data, etc. In practice, numerical weights representing severity of residual disability are established by the judgment of patients and health professionals. Procedures for calculating QALYs, like those for calculating DALYs, begin with chronological age and multiply this by a “utility-weight” for the health state. A variety of techniques have been used, including standard gamble and time trade-off. See also disability-adjusted life years.

QUALITY ASSURANCE System of procedures, checks, audits, and corrective actions to ensure that all research, testing, monitoring, sampling, analysis, and other technical and reporting activities are of the highest achievable quality. The term is used in health services with the same meaning.

QUALITY CONTROL The supervision and control of all operations involved in a process, usually involving sampling and inspection, in order to detect and correct systematic or excessively random variations in quality.

QUALITY OF CARE A level of performance or accomplishment that characterizes the health care provided. Ultimately, measures of the quality of care always depend upon value judgments, but there are ingredients and determinants of quality that can be mea- sured objectively. These ingredients and determinants were classified by Donabedian329 into measures of structure (e.g., manpower, facilities), process (e.g., diagnostic and therapeutic procedures), and outcome (e.g., case fatality rates, disability rates, and levels of patient satisfaction with the service). See also health services research.


  1. The degree to which persons perceive themselves able to function physically, emotionally, mentally, and socially. Contrast health status, which is an objective measurement. In a general sense, that which makes life worth living.
  2. In a more “quantitative” sense, an estimate of remaining life free of impairment, disability, or handicap, as used in the expression quality-adjusted life years. Somewhere between these is an estimate of the utility of life; for instance, in clinical decision analysis, the utility of life that is impaired by a disabling degree of angina pectoris may be compared with that of a life that may be shorter in duration but free of disabling pain as a result of applying therapeutic procedures. Such trade-offs are part of clinical decision analysis. See also utility.

QUOROM Quality of Reporting of Meta-analyses. A consensus checklist and a flow diagram to improve the quality of reports of meta-analyses of randomized clinical trials.95,106,330 The checklist describes ways to present the abstract, introduction, methods, results, and discussion sections of a report of a meta-analysis. The flow diagram pro- vides information about the numbers of trials identified, included, and excluded and the reasons for exclusion of trials. See also consort; moose; quadas; stard; strobe; trend.

QUANGO A semipublic body partly or wholly supported by government funds and with some members appointed by the government but otherwise having the characteristics of a nongovernmental organization, i.e., a quasi-autonomous NGO, hence the name, originally slang. A term used mainly in Britain.

QUANTAL EFFECT (Syn: all-or-none effect) An effect that can be expressed only in binary form, e.g., as “occurring” or “not occurring.”200

QUANTILES Divisions of a distribution into equal, ordered subgroups. Deciles are tenths; quartiles, quarters; quintiles, fifths; terciles, thirds; and centiles, hundredths.

QUANTITATIVE DATA Data in numerical quantities, such as continuous measurements or counts.


1. Restriction of the activities of well persons or animals who have been exposed to a case of communicable disease during its period of communicability (i.e., contacts) to prevent disease transmission during the incubation period if infection should occur. a. Absolute or complete quarantine: The limitation of freedom of movement of those exposed to a communicable disease for a period of time not longer than the longest usual incubation period of that disease in such manner as to prevent effective contact with those not so exposed.
b. Modified quarantine: A selective, partial limitation of freedom of movement of contacts, commonly on the basis of known or presumed differences in susceptibility and related to the danger of disease transmission. It may be designed to meet particular situations. Examples are exclusion of children from school, exemption of immune persons from provisions applicable to susceptible persons, or restriction of military populations to the post or to quarters. It includes personal surveillance, the practice of close medical or other supervision of contacts in order to permit prompt recognition of infection or illness but without restricting movements; and segregation, the separation of some part of a group of persons or domestic animals from the others for special consideration, control, or observation — for example, removal of susceptible children to homes of immune persons or establishment of a sanitary boundary to protect uninfected from infected portions of a population.52

2. The word quarantine comes from the Italian quaranta, meaning forty, and refers to the 40 days arbitrarily (or empirically) believed to be an adequate isolation period, perhaps based on the biblical 40 days. The clinical distinction between isolation and quarantine is that isolation is the procedure for persons already sick, whereas quarantine is often applied to (apparently) healthy contacts. This has legal and ethical implications if apparently healthy persons must submit to restrictions upon their freedom to move at large in society. See also isolation.

QUASI-EXPERIMENT A situation in which the investigator lacks full control over the allocation and/or timing of intervention but nonetheless conducts the study as if it were an experiment, allocating subjects to groups. Inability to allocate subjects randomly is a common situation that may be best described as a quasi-experiment. See also natural experiment.

QUESTIONNAIRE A predetermined set of questions used to collect data—clinical data, social status, occupational group, etc. This term is often applied to a self-completed sur- vey instrument, as contrasted with an interview schedule.

QUETELET’S INDEX See body mass index.

QUEUEING THEORY A mathematical discipline featuring models that analyze the flow of people through a service or their use of resources and that attempts to optimize utilization.

“QUICK AND DIRTY” METHOD A colloquial expression to refer to a method that yields a result rapidly but not necessarily with scientific rigor or validity. At least one variety, rapid epidemiological assessment, has value and is not necessarily “dirty” (i.e., unreliable).

QUOTA SAMPLING A method by which the proportions in the sample in various sub- groups (according to criteria such as age, sex, and social status of the individuals to be selected) are chosen to agree with the corresponding proportions in the population. The resulting sample may not be representative of characteristics that have not been taken into account.

QUOTIENT The result of the division of a numerator by a denominator.