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Term |
Definition/Description |
Comment |
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Absolute risk reduction |
A measure of treatment effect that compares the probability (or mean) of a type of outcome in the control group with that of a treatment group, [i.e.: Pc - Pt (or µc - µt)]. For instance, if the results of a trial were that the probability of death in a control group was 25% and the probability of death in a treatment group was 10%, the absolute risk reduction would be (0.25 - 0.10) = 0.15. (See also Number needed to treat, Odds ratio, and Relative risk reduction)
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Access |
The degree to which the health care system aids or inhibits an individual or group in gaining entry and receiving necessary services due to constraints in the financing and delivery of care.
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Accuracy |
The degree to which a measurement (e.g. the mean estimate of a treatment effect) is true or correct. An estimate can be accurate, yet not be precise, if it is based upon an unbiased method that provides observations having great variation (i.e. not close in magnitude to each other). (See also Precision)
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Acquisition cost |
The purchase cost of a drug to an institution, agency or person.
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Action research (or participatory action research) |
Where a problem is identified, investigated and changes are made; then reassessed and further changes made, until the problem is satisfactorily resolved.
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Additive model |
A model in which the combined effect of several factors is the sum of the effects produced by each of the factors. For example, if one factor multiplies risk by a and a second factor by b, the combined effect of the two factors is a + b. (See also Multiplicative model)
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Adverse effect |
An undesirable or unintended effect of an intervention. (See also Adverse event and Side effect)
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Adverse event |
Any noxious, pathological or unintended change in anatomical, physical or metabolic functions as indicated by physical signs, symptoms and/or laboratory changes occurring in any phase of a clinical study whether or not considered treatment related. It includes exacerbation of pre-existing conditions or events, intercurrent illnesses, accidents, drug interaction or the significant worsening of disease.
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Adverse reaction |
Any undesirable or unwanted consequence of a preventive, diagnostic, or therapeutic procedure in a standard clinical setting.
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Allocative efficiency |
An allocation of the mix of resources for maximal benefit (i.e. such that no change in spending priorities could improve the overall welfare).
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Alpha (a) |
Alpha (α): the probability of a Type I (false-positive) error. In hypothesis testing, the α-level is the threshold for defining statistical significance. For instance, setting α at a level of 0.05 implies that investigators accept that there is a 5% chance of concluding incorrectly that an intervention is effective when it has no true effect. The α-level is commonly set at 0.01 or 0.05 or 0.10. (See also Hypothesis testing)
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Annualisation |
A means of converting capital costs into an annual figure based upon the equipment lifespan, initial cost, end of lifespan value and financial interest rate.
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Applicability |
The degree to which the results of an observation, study or review hold true in other settings. (See also External validity and Generalizability).
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Analytic perspective |
The viewpoint chosen for the analysis (e.g. societal, government, health care system, payer).
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Arithmetic mean |
See Mean.
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Assessment |
A scientific process of examining and reporting properties of a technology used in health care, such as safety, efficacy, feasibility and indications for use, cost and cost-effectiveness, as well as social, economic and ethical consequences.
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Attrition bias |
Systematic differences between comparison groups in withdrawals or exclusions of participants from the results of a study. For example, patients may drop out of a study because of adverse reactions of the intervention. Excluding these patients from the analysis could result in an overestimate of the effectiveness of the intervention.
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Audit |
The process of setting and adopting standards and measuring performance against those standards with the aim of identifying both good and bad practice.
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Autonomy |
The patient’s right of self-determination concerning medical care. It may be used in various senses including freedom of action, effective deliberation and authenticity. It supports such moral and legal principles as respect for persons and informed consent. Making decisions for oneself, in light of a personal system of values and beliefs.
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Average cost |
Total costs of a treatment or programme divided by total quantity of treatment units provided. (See also Marginal cost)
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Bayesian analysis |
A statistical approach that can be used in single studies or meta-analysis which explicitly incorporates a prior probability distribution based on subjective opinion and objective evidence, such as the results of previous research. Bayesian analysis uses Bayes' theorem to update the prior distribution in light of the results of a study, producing a posterior distribution. Statistical inferences (point estimates, confidence intervals, etc.) are probability based on this posterior distribution. The posterior distribution also acts as the prior distribution for the next study. This approach has many attractive features, but is controversial because it may depend on opinions, and frequently they will vary considerably. However, its use has become commonplace in Economic evaluation as it allows creation of complex models with different evidence sources and determination of uncertainty.
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Before-and-after study (pre-test/post-test study) |
A study design where a group is studied before and after an intervention. Interpretation of the result is problematic, as it is difficult to separate the effect of the intervention from the effect of other factors. |
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Benchmarking |
A quality assurance process in which an organization sets goals and measures its performance in comparison to those of the products, services, and practices of other organizations that are recognized as leaders.
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Beta (β) |
The probability of a Type II (false-negative) error. In hypothesis testing, β is the probability of concluding incorrectly that an intervention is not effective when it has true effect. (1-β) is the Power to detect an effect of an intervention if one truly exists. (See also Hypothesis testing)
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Bias |
In general, any factor that distorts the true nature of an event or observation. In clinical investigations, a bias is any systematic factor other than the intervention of interest that affects the magnitude of (i.e. tends to increase or decrease) an observed difference in the outcomes of a treatment group and a control group. Bias diminishes the accuracy (though not necessarily the precision) of an observation. Randomization is a technique used to decrease this form of bias. Bias also refers to a prejudiced or partial viewpoint that would affect someone's interpretation of a problem. Double blinding is a technique used to decrease this type of bias.
(See also Attrition bias, Detection bias, Performance bias, Publication bias, Selection bias and Workup bias)
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Bibliographic database |
An indexed computer or printed source of citations of journal articles and other reports in the literature. Bibliographic citations typically include author, title, source, abstract, and/or related information (including full text in some cases). Examples are MEDLINE and EMBASE.
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Binary data (dichotomous data) |
Observations with two possible categories such as dead/alive, smoker/non-smoker, present/not present. |
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Blinding (masking) |
Also known as “masking,” the knowledge of patients and/or investigators about whether individual patients are receiving the investigational intervention(s) or the control (or standard) intervention(s) in a clinical trial. Blinding is intended to eliminate the possibility that knowledge of which intervention is being received will affect patient outcomes or investigator behaviors that may affect outcomes. Blinding is not always practical (e.g. when comparing surgery to drug treatment), but it should be used whenever it is possible and compatible with optimal patient care.
(See also Concealment of allocation, Single blind, Double blind and Triple blind)
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Budget impact analysis |
The financial impact of the introduction of a technology or service on the capital and operating budgets of a government or agency.
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Capital costs |
The non-recurring cost of investment in items that remains useful beyond the period when costs are incurred.
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Case |
A person in the study group who has the disease or characteristic of interest.
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Case-control study |
A retrospective observational study designed to determine the relationship between a particular outcome of interest (e.g. disease or condition) and a potential cause (e.g. an intervention, risk factor, or exposure). Investigators identify a group of patients with a specified outcome (cases) and a group of patients without the specified outcome (controls). Investigators then compare the histories of the cases and the controls to determine the rate or level at which each group experienced a potential cause. As such, this study design leads from outcome (disease or condition) to cause (intervention, risk factor, or exposure).
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Case-mix |
Features of a study population that may influence the outcome or the choice of treatment (e.g. severity of disease, coexisting conditions); such features must be taken into account when assessing treatment outcomes.
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Case report (case study) |
An uncontrolled (prospective or retrospective) observational study involving an intervention and outcome in a single patient. (Also known as a single case report or anecdote.)
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Case series |
An uncontrolled study (prospective or retrospective) of a series (succession) of consecutive patients who receive a particular intervention and are followed to observe their outcomes. (Also known as case series or clinical series or series of consecutive cases.)
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Categorical data |
Data that are classified into more than two categories where there is not necessarily a natural order to the categories; for example treatment centres. (See also Ordinal data.)
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Causal pathway |
Also known as an “analytical framework,” a depiction (e.g. in a schematic) of direct and indirect linkages between interventions and outcomes. For a clinical problem, a causal pathway typically includes a patient population, one or more alternative interventions (e.g. screening, diagnosis, and/or treatment), intermediate outcomes (e.g. biological markers), and health outcomes. Causal pathways are intended to provide clarity and explicitness in defining the questions to be addressed in an assessment; they are useful in identifying pivotal linkages for which evidence may be lacking.
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Causality |
The relating of causes to the effects they produce. The Bradford Hill criteria for causal association are: consistency; strength; specificity; dose–response relationship; temporal relationship (exposure always precedes the outcome; it is the only essential criterion); biological plausibility; coherence; and experiment.
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CINAHL (Cumulative Index to Nursing and Allied Health Literature) |
Electronic database covering the literature in nursing and allied health. Years of coverage: 1982 - present. |
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Citation |
The record of an article, book, or other report in a bibliographic database that includes summary descriptive information, e.g. authors, title, abstract, source, and indexing terms.
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Clinical effectiveness (effectiveness) |
The extent to which a specific intervention, procedure, regimen, or service does what it is intended to do under ordinary circumstances, rather than controlled conditions. Or more specifically, the evaluation of benefit to risk of an intervention, in a standard clinical setting, using outcomes measuring issues of importance to patients (e.g. ability to do daily activities, longer life, etc.).
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Clinical (practice) guideline |
A systematically developed statement to assist practitioner and patient decisions about appropriate health care for one or more specific clinical circumstances. The development of clinical practice guidelines can be considered to be a particular type of HTA; or, it can be considered to be one of the types of policymaking that is informed or supported by HTA
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Clinical outcome |
An outcome of major clinical importance that is defined on the basis of the disease being studied (e.g. fracture in osteoporosis, peptic ulcer healing and relapse rates).
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Clinical pathway |
A multidisciplinary set of daily prescriptions and outcome targets for managing the overall care of a specific type of patient, e.g. from pre-admission to post-discharge for patients receiving inpatient care. Clinical pathways often are intended to maintain or improve quality of care and decrease costs for patients in particular diagnosis-related groups.
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Clinical prediction |
A clinical prediction rule is a tool for assisting clinical decision making, which consists of variables obtained from the patient’s history, physical exam, or testing that provide the probability of an outcome or suggest a diagnostic or therapeutic course of action.
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Clinical significance |
A conclusion that an intervention has an effect that is of practical meaning to patients and health care providers. Even though an intervention is found to have a statistically significant effect, this effect might not be clinically significant. In a trial with a large number of patients, a small difference between treatment and control groups may be statistically significant but clinically unimportant. In a trial with few patients, an important clinical difference may be observed that does not achieve statistical significance. (A larger trial may be needed to confirm that this is a statistically significant difference.)
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Clinical trial |
A carefully controlled and monitored research study on human subjects or patients evaluating one or more health interventions (including diagnostic methods and prophylactic interventions). Each trial is designed to answer specific scientific questions.
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Cochrane Central Register of Controlled Trials (CENTRAL) |
A database of references to controlled trials in health care compiled from the specialised registers of the Cochrane groups and other organisations, searches of MEDLINE, EMBASE and other databases.
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Cochrane Database of Methodology Reviews (CDMR) |
The CDMR contains two parts: Cochrane Methodology Reviews (complete systematic reviews of methodological studies) and Protocols for reviews that are currently in progress.
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Cochrane Methodology Register (CMR) |
A database of articles and books about methods for conducting systematic reviews of the effects of health care interventions. It is published in The Cochrane Library.
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Cochrane Database of Systematic Reviews (CDSR) |
This database includes the full text of all available Cochrane Collaboration systematic reviews, and the procotols for reviews that are currently underway. (See also The Cochrane Library) |
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The Cochrane Library |
A collection of databases published on CD-ROM and the Internet and updated quarterly, designed to provide information and evidence to support decision making in health care. The databases are as follows: the Cochrane Database of Systematic Reviews, the Cochrane Database of Methodology Reviews, the Cochrane Central Register of Controlled Trials, the Database of Abstracts of Reviews of Effects, the Cochrane Methodology Register, the Health Technology Assessment database and the NHS Economic Evaluation database.
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Cochrane Methodology Register (CMR) |
A bibliography of publications which report on the methods used in the conduct of controlled trials. It is published in The Cochrane Library.
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Cohort study |
An observational study in which outcomes in a group of patients that received an intervention are compared with outcomes in a similar group i.e. the cohort, either contemporary or historical, of patients that did not receive the intervention. In an adjusted- (or matched-) cohort study, investigators identify (or make statistical adjustments to provide) a cohort group that has characteristics (e.g. age, gender, disease severity) that are as similar as possible to the group that experienced the intervention.
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Cointervention |
In a randomized controlled trial, the application of additional diagnostic or therapeutic procedures to members of either or both the experimental and the control groups.
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Comorbidity |
The presence of co-existing or additional diseases to the one being studied.
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Comparator |
The technology to which an intervention is compared. |
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Compliance |
A measure of the extent to which patients undergo an assigned treatment or regimen, e.g. taking drugs, undergoing a medical or surgical procedure, doing an exercise regimen, or abstaining from smoking.
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Concealment of allocation |
The process used to assign patients to alternative groups in an RCT in a manner that prevents foreknowledge (by the person managing the allocation as well as the patients) of this assignment. Medical record numbers, personal identification numbers, or birthdays are not adequate for concealment of allocation. Certain centralized randomization schemes and sequentially numbered sealed, opaque envelopes are among adequate methods of allocation concealment. (See also Blinding)
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Concurrent control |
A control group that is observed by investigators at the same time as the treatment group, but that was not established using random assignment of patients to control and treatment groups. Differences in the composition of the treatment and control groups may result.
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Confidence interval (CI) |
Depicts the range of uncertainty about an estimate of a treatment effect. It is calculated from the observed differences in outcomes of the treatment and control groups and the sample size of a study. The confidence interval (CI) is the range of values above and below the point estimate that is likely to include the true value of the treatment effect. The use of CIs assumes that a study provides one sample of observations out of many possible samples that would be derived if the study were repeated many times. Investigators typically use CIs of 90%, 95%, or 99%. For instance, a 95%
CI indicates that there is a 95% probability that the CI calculated from a particular study includes the true value of a treatment effect. If the interval includes a null treatment effect (usually 0.0, but 1.0 if the treatment effect is calculated as an odds ratio or relative risk), the Null hypothesis of no true treatment effect cannot be rejected.
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Confidence profile method |
A type of meta-analysis based on Bayesian statistics for combining results of multiple studies of various design (e.g. RCTs, observational studies, and others) that adjusts the individual studies for their respective methodological biases before combining their results into a probability distribution for the parameter(s) of interest.
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Confidentiality |
The professional-client promise not to reveal information without consent.
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Conflict of interest |
A situation in which the private interests of someone involved in the assessment or evaluation process (e.g. interviewer, rater, scorer, evaluator) have an impact (either positive or negative) on the quality of the evaluation activities, the accuracy of the data, or the results of the evaluation.
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Conflict of interest declaration (register of interest) |
A statement by a contributor to a report or review of personal financial or other interests that could have influenced the findings or their interpretation.
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Confounding factor |
A factor that is causally linked to the treatment (exposure) and the outcome under study. For example, if cancer incidence is compared between heavy drinkers and tea-totallers, smoking is a confounder (i.e. more heavy drinkers smoke and this is related to cancer) and so smoking should be carefully ascertained and evaluated in the analysis.
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Consensus development |
Various forms of group judgment in which a group (or panel) of experts interacts in assessing an intervention and formulating findings by vote or other process of reaching general agreement. These process may be informal or formal, involving such techniques as the nominal group and Delphi techniques.
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Consensus report |
A statement or practice based on general or majority agreement within a group.
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Consequence(s) |
The outcome(s) associated with a disease and/or intervention (e.g. stroke, death, side effects, avoided morbidity).
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Consumer (patient, user) |
Someone who uses, is affected by, or who is entitled or compelled to use a health related service.
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Consumer advocate (patient representative) |
Consumer who is actively involved with other consumers and able to represent the perspectives and concerns of that broader group of people.
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Contamination |
In clinical trials, the inadvertent application of the intervention being evaluated to people in the control group or inadvertent failure to apply the intervention to people assigned to the intervention group.
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Context |
The conditions and circumstances that are relevant to the application of an intervention, for example the setting [in hospital, at home, in the air], the time [working day, holiday, night-time], type of practice [primary, secondary, tertiary care; private practice, insurance practice, charity], whether routine or emergency.
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Context bias |
The influence of the study context on the interpretation of test results; for example, in groups with high prevalence of disease, readers may be more likely to interpret test results as abnormal.
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Contingency table |
A tabular cross-classification of data such that subcategories of one characteristic are indicated horizontally (in rows) and subcategories of another characteristic are indicated vertically (in columns). Tests of association between the characteristics can be readily applied. The simplest contingency table is the fourfold, or 2x2 table, which is used in clinical trials to compare dichotomous outcomes, such as death, for an intervention and control group or two intervention groups.
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Contingent valuation |
A method for evaluation of benefit or value to individuals of therapy that uses survey methods to establish willingness to pay.
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Continuous data |
Data with a potentially infinite number of possible values along a continuum. Height, weight and blood pressure are examples of continuous variables.
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Contraindication |
A clinical symptom or circumstance indicating that the use of an otherwise advisable intervention would be inappropriate.
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Control |
1. In clinical trials comparing two or more interventions, a control is a person in the comparison group that receives a placebo, no intervention or standard care.
2. In case-control studies a control is a person in the comparison group without the disease or outcome of interest.
3. In statistics control means to adjust for or take into account extraneous influences or observations.
4. Control can also mean programs aimed at reducing or eliminating the disease when applied to communicable (infectious) diseases.
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Control group |
A group of patients that serves as the basis of comparison when assessing the effects of the intervention of interest that is given to the patients in the treatment group. Depending upon the circumstances of the trial, a control group may receive no treatment, a "usual" or "standard" treatment, or a placebo. To make the comparison valid, the composition of the control group should resemble that of the treatment group as closely as possible. (See also Historical control)
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Controlled clinical trial (CCT) |
A prospective experiment in which investigators compare outcomes of a group of patients receiving an intervention to a group of similar patients not receiving the intervention. Not all clinical trials are RCTs, though all RCTs are clinical trials.
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Controlled vocabulary |
A system of terms, involving, e.g. definitions, hierarchical structure, and cross-references, that is used to index and retrieve a body of literature in a bibliographic, factual, or other database. An example is the MeSH controlled vocabulary used in MEDLINE and other MEDLARS databases of the NLM.
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Correlation coefficient |
A numeric measure between -1 and 1 that expresses the strength of observed linear association between two variables; expressed as r, the value r = 0 indicates either the lack of a linear relationship or a possible nonlinear relationship between the two variables.
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Cost-benefit analysis |
A comparison of alternative interventions in which costs and outcomes are quantified in common monetary units
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Cost-consequence analysis (CCA) |
A form of cost-effectiveness analysis in which the components of incremental costs (of therapies, hospitalization, etc.) and consequences (health outcomes, adverse effects, etc.) of alternative interventions or programs are computed and displayed, without aggregating these results (e.g. into a cost-effectiveness ratio).
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Cost-effectiveness acceptability curve (CEAC) |
A plot of the probability that an intervention is cost effective, as a function of the value assigned to an additional quality adjusted life year (QALY). |
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Cost-effectiveness analysis (CEA) |
A comparison of alternative interventions in which costs are measured in monetary units and outcomes are measured in non-monetary units, e.g. reduced mortality or morbidity. (See also Cost per QALY)
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Cost-minimization analysis (CMA) |
A determination of the least costly among alternative interventions that are assumed to produce equivalent outcomes.
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Cost of illness analysis |
A determination of the economic impact of a disease or health condition, including treatment costs; this form of study does not address benefits/outcomes.
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Cost of lost time |
The cost of time lost from work and decreased productivity due to disease, disability, or death. Value of time commonly based on the average wage/earnings rate.
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Cost per QALY |
A measure used in CUA to assist in comparisons among programmes; expressed as monetary cost per unit of outcome.
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Cost-utility analysis (CUA) |
A form of cost-effectiveness analysis of alternative interventions in which costs are measured in monetary units and outcomes are measured in terms of their utility, usually to the patient, e.g. using QALYs.
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Credible interval |
The Bayesian equivalent of a confidence interval. The probability of a X% credible interval containing the true value is X/100. For example, a 95% credible interval of (0.82, 1.36) for the odds ratio for mortality would imply that the probability that this odds ratio was between 0.82 and 1.36 is 0.95.
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Critical appraisal |
The process of assessing and interpreting evidence by systematically considering its validity, results and relevance.
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Cross-sectional study
(prevalence study) |
A (prospective or retrospective) observational study in which a group is chosen (sometimes as a random sample) from a certain larger population, and the exposures of people in the group to an intervention and outcomes of interest are determined. |
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Crossover bias |
Occurs when some patients who are assigned to the treatment group in a clinical study do not receive the intervention or receive another intervention, or when some patients in the control group receive the intervention (e.g. outside the trial). If these crossover patients are analyzed with their original groups, this type of bias can "dilute" (diminish) the observed treatment effect.
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Crossover design |
A clinical trial design in which patients receive, in sequence, the treatment (or the control), and then, after a specified time, switch to the control (or treatment). In this design, patients serve as their own controls, and randomization may be used to determine the order in which a patient receives the treatment and control.
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Crossover trial (study) |
A trial in which patients receive, in sequence, the treatment (or the control), and then, after a specified time, switch to the control (or treatment). In this design, patients serve as their own controls, and randomization is used to determine the order in which a patient receives the treatment and control. A problem with this design is that the effects of the first treatment may carry over into the period when the second is given and so washout periods between periods are often used.
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Cumulative meta-analysis |
In cumulative meta-analysis studies are added one at a time in a specified order (e.g. according to date of publication or quality) and the results are summarised as each new study is added. In a graph of a cumulative meta-analysis each horizontal line represents the summary of the results as each study is added, rather than the results of a single study. However, such analyses are subject to bias unless the multiple testing aspects are adequately accounted for. (See also Sequential trial)
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DALY |
See Disability-adjusted life years
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Database (or register) |
Any of a wide variety of repositories (often computerized) for observations and related information about a group of patients (e.g. adult males living in Göteborg) or a disease (e.g. hypertension) or an intervention (e.g. antihypertensive drug therapy) or other events or characteristics. Depending upon criteria for inclusion in the database, the observations may have controls. Although these can be useful, a variety of confounding factors (e.g. no randomization and possible selection bias in the process by which patients or events are recorded) make them relatively weak methods for determining causal relationships between an intervention and an outcome.
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Database of Abstracts of Reviews of Effects (DARE) |
DARE is a database of quality assessed systematic reviews of the effects of health care interventions. (See also The Cochrane Library)
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Decision analysis |
An approach to decision making under conditions of uncertainty that involves modeling of the sequences or pathways of multiple possible strategies (e.g. of diagnosis and treatment for a particular clinical problem) to determine which is optimal. It is based upon available estimates (drawn from the literature or from experts) of the probabilities that certain events and outcomes will occur and the values of the outcomes that would result from each strategy. A decision tree is a graphical representation of the alternate pathways.
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Decision tree |
A framework for representing alternatives for use in decision analysis.
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Degrees of freedom |
The number of independent comparisons that can be made between the members of a sample. It refers to the number of independent contributions to a sampling distribution (such as chi-square distribution). In a contingency table it is one less than the number of row categories multiplied by one less than the number of column categories; e.g. a 2 x 2 table comparing two groups for a dichotomous outcome, such as death, has one degree of freedom.
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Delphi technique |
An iterative group judgment technique in which a central source forwards surveys or questionnaires to isolated, anonymous (to each other) participants whose responses are collated/summarized and recirculated to the participants in multiple rounds for further modification/critique, producing a final group response (sometimes statistical). See also Nominal group technique
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Detection bias |
Systematic differences between comparison groups in ascertainment, diagnosis or verification of outcomes.
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Diagnosis |
Identification of an illness or diseases by means of its signs, symptoms and results of investigations. This involves ruling out other illnesses and causal factors for the clinical manifestations.
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Diagnostic accuracy |
See Accuracy
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Diagnostic impact |
A characteristic of Diagnostic test efficacy describing the effect of test results on diagnosis.
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Diagnostic test efficacy |
The impact and usefulness of a diagnostic test expressed in terms of its technical properties, Diagnostic accuracy, Diagnostic impact, therapy, patient outcome, or society.
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Dichotomous data |
See Binary data
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Diffusion of innovation |
The process by which an innovation is communicated through certain channels over time among the members of a social system. In the case of medical technologies this would be the factors influencing the adoption of a new technology within the health care system.
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Dilemma |
A forced choice between courses of action (usually two) which are equally unacceptable.
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Direct costs |
The fixed and variable costs of all resources (goods, services, etc.) consumed in the provision of an intervention as well as any consequences of the intervention such as adverse effects or goods or services induced by the intervention. Includes direct medical costs and direct nonmedical costs such as transportation or child care.
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