See risk difference.

See concealment of allocation.

(synonyms: external validity, generalisability, relevance, transferability)
The degree to which the results of an observation, study or review hold true in other settings.

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 side effects of the intervention. Excluding these patients from the analysis could result in an overestimate of the effectiveness of the intervention.

A systematic error or deviation in results or inferences. In studies of the effects of healthcare, bias can arise from systematic differences in the groups that are compared (selection bias), the care that is provided, or exposure to other factors apart from the intervention of interest (performance bias), withdrawals or exclusions of people entered into the study (attrition bias) or how outcomes are assessed (detection bias). Bias does not necessarily imply a prejudice, such as the investigators' desire for particular results. This differs from conventional use of the word in which bias refers to a partisan point of view. See also methodological quality, validity.

(synonym: masking) Keeping secret group assignment (e.g. to treatment or control) from the study participants or investigators. Blinding is used to protect against the possibility that knowledge of assignment may affect patient response to treatment, provider behaviours (performance bias) or outcome assessment (detection bias). Blinding is not always practical (e.g. when comparing surgery to drug treatment). The importance of blinding depends on how objective the outcome measure is; blinding is more important for less objective outcome measures such as pain or quality of life. See also single blind, double blind and triple blind.

An uncontrolled observational study involving an intervention and outcome for more than one person.

(synonyms: anecdote, case history, single case report) An uncontrolled observational study involving an intervention and outcome for a single person (or other unit).

See Cochrane Controlled Trials Register.

See Cochrane Database of Systematic Reviews.

The Cochrane Collaboration's register of studies which may be relevant for inclusion in Cochrane Reviews. Its development is guided by the CENTRAL/CCTR Advisory Group. See also Cochrane Controlled Trials Register.

Any statistical test based on comparison of a test statistic to a chi-square distribution.

See Confidence interval

(Cumulative Index of Nursing and Allied Health Literature) Electronic database covering the major journals in nursing and allied health. Years of coverage: 1983 - present.

A systematically developed statement for practitioners and patients about appropriate health care for specific clinical circumstances. (e.g. Scottish Intercollegiate or SIGN guidelines, Royal College of Physicians guidelines etc.)

(synonyms: therapeutic trial, intervention study) A trial that tests out a drug or other intervention to assess its effectiveness and safety. This general term encompasses randomised controlled trials and controlled clinical trials.

An international organisation that aims to help people make well informed decisions about health by preparing, maintaining and ensuring the accessibility of systematic reviews of the benefits and risks of healthcare interventions.

(CCTR) A database of references to controlled trials in health care. Cochrane groups and other organisations have been invited to contribute their specialised registers, and these registers, together with references to clinical trials identified on MEDLINE and other sources, form the CENTRAL register of studies. Records from CENTRAL, following quality control to try to ensure that only reports of definite randomised controlled trials or controlled clinical trials are included, make up The Cochrane Controlled Trials Register (CCTR). Trials included in the STEP process are derived from the Cochrane Stroke Group.

(CDSR) It brings together all the currently available Cochrane Reviews and is updated quarterly.

A Cochrane Review is a systematic, up-to-date summary of reliable evidence of the benefits and risks of healthcare. Cochrane Reviews are intended to help people make practical decisions.

In a randomised controlled trial, the application of additional diagnostic or therapeutic procedures to members of either or both the experimental and the control groups.

The process used to prevent foreknowledge of group assignment in a randomised controlled trial, which should be seen as distinct from blinding. The allocation process should be impervious to any influence by the individual making the allocation by having the randomisation process administered by someone who is not responsible for recruiting participants; for example, a hospital pharmacy, or a central office. Using methods of assignment such as date of birth and case record numbers (see quasi random allocation) are open to manipulation. Adequate methods of allocation concealment include: centralized randomisation schemes; randomisation schemes controlled by a pharmacy; numbered or coded containers in which capsules from identical-looking, numbered bottles are administered sequentially; on-site computer systems, where allocations are in a locked unreadable file; and sequentially numbered opaque, sealed envelopes.

(CI) The range within which the "true" value (e.g. size of effect of an intervention) is expected to lie with a given degree of certainty (e.g. 95% or 99%). Note: Confidence intervals represent the probability of random errors, but not systematic errors (bias).

[or Competing interests declaration] 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.

A situation in which a measure of the effect of an intervention or exposure is distorted because of the association of exposure with other factor(s) that influence the outcome under investigation.

(healthcare consumer) Someone who uses, is affected by, or who is entitled or compelled to use a health related service.

In clinical trials, the unintentional 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.

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.

In clinical trials comparing two or more interventions, a control is a person in the comparison group that receives a placebo, no intervention, usual care or another form of care.

Refers to a study that compares one or more intervention groups to one or more comparison (control) groups. Whilst not all controlled studies are randomised, all randomised trials are controlled.

The process of assessing and interpreting evidence by systematically considering its validity, results and relevance.

A type of clinical trial comparing two or more interventions in which the participants, upon completion of the course of one treatment are switched to another. For example, for a comparison of treatments A and B, half the participants are randomly allocated to receive them in the order A, B and half to receive them in the order B, A. A problem with this design is that the effects of the first treatment may carry over into the period when the second is given.

See Database of Abstracts of Reviews of Effectiveness.

A collection of organised information, usually held on a computer. In some ways a database is similar to a filing system, but with important advantages: the information can be revised and kept up to date easily, and the computer can retrieve information from it very quickly. Electronic databases such as MEDLINE, EMBASE and the CDSR can be distributed on disk, CD-ROM or via the Internet.

(DARE) A collection of structured abstracts and bibliographic references of systematic reviews of the effects of healthcare.

(synonym: ascertainment bias) Systematic differences between comparison groups in how outcomes are ascertained, diagnosed or verified.

(synonym: binary data) Observations with two possible categories such as dead/alive, smoker/non-smoker, present/not present.

(synonym: double masked) Neither the participants in a trial nor the investigators (outcome assessors) are aware of which intervention the participants are given. The purpose of blinding the participants (recipients and providers of care) is to prevent performance bias. The purpose of blinding the investigators (outcome assessors, who might also be the care providers) is to protect against detection bias. See also blinding, single blind, triple blind, concealment of allocation.

1. A generic term for the estimate of effect for a study. 2. A dimensionless measure of effect that is typically used for continuous data when different scales (e.g. for measuring pain) are used to measure an outcome and is usually defined as the difference in means between the intervention and control groups divided by the standard deviation of the control or both groups. See standardised mean difference.

The extent to which a specific intervention, when used under ordinary circumstances, does what it is intended to do.