Blinding (masking): in an experimental study, refers to whether patients, clinicians providing an intervention, people assessing outcomes, and/or data analysts were aware or unaware of the group to which patients were assigned. In the design section of Evidence-Based Nursing abstracts of treatment studies, the study is identified as blinded, with specification of who was blinded; unblinded, if all parties were aware of patients' group assignments; or blinded (unclear) if the authors did not report or provide us with an indication of who was aware or unaware of patients' group assignments.

Concealment of randomisation: concealment of randomisation is specified in the design section of Evidence-Based Nursing abstracts of treatment studies as follows: allocation concealed (deemed to have taken adequate measures to conceal allocation to study group assignments from those responsible for assessing patients for entry in the trial [ie, central randomisation; sequentially numbered, opaque, sealed envelopes; sealed envelopes from a closed bag; numbered or coded bottles or containers; drugs prepared by the pharmacy; or other descriptions that contain elements convincing of concealment]); allocation not concealed (deemed to have not taken adequate measures to conceal allocation to study group assignments from those responsible for assessing patients for entry in the trial [ie, no concealment procedure was undertaken, sealed envelopes that were not opaque or were not sequentially numbered, or other descriptions that contained elements not convincing of concealment]); unclear allocation concealment (the authors did not report or provide a description of an allocation concealment approach that allowed for the classification as concealed or not concealed).

Confidence interval (CI): quantifies the uncertainty in measurement; usually reported as 95% CI, which is the range of values within which we can be 95% sure that the true value for the whole population lies.

Data saturation (saturation, redundancy)¹: process of collecting data in a qualitative research study to the point where no new themes are generated.

Diagnostic (gold or criterion) standard: the current best available measure of an outcome; used for assessing properties of a new diagnostic or screening test. The results from a new test are compared with the results from the diagnostic standard to assess the usefulness of the new test (ie, its sensitivity, specificity, and likelihood ratios).

Ethnography (ethnographic study)¹: an approach to inquiry that focuses on the culture or subculture of a group of people, with an effort to understand the world view of those under study.

Grounded theory¹: an approach to collecting and analysing qualitative data with the aim of developing theories grounded in real world observations.

Heterogeneity²: the degree to which the effect estimates of individual studies in a meta-analysis differ significantly.

Inductive analysis: often used in qualitative research, this type of analysis begins with specific observations from which generalisations are developed; opposite to deductive analysis, often used in quantitative research, which begins with the abstract (eg, general laws or hypotheses) from which logical deductions about specific things are made.

Intention to treat analysis (ITT): all patients are analysed in the groups to which they were randomised, even if they failed to complete the intervention or received the wrong intervention.

Kappa: a statistic that indicates the extent of agreement between 2 or more observers beyond that expected by chance. A kappa of 1.0 indicates perfect agreement.

Likelihood ratio (for positive and negative results)³: A way of summarising the findings of a study of a diagnostic test for use in clinical situations where there may be differences in the prevalence of the disease. The likelihood ratio for a positive test is the likelihood that a positive test result comes from a person who really does have the disorder rather than one who does not have the disorder (sensitivity/1−specificity). The likelihood ratio for a negative test is the likelihood that a negative test result comes from a person with the disorder rather than one without the disorder (1−sensitivity/specificity).

Meta-analysis⁴: a method for combining the results of several independent studies that measure the same outcomes so that an overall summary statistic can be calculated.

Number needed to treat (NNT): number of patients who need to be treated to prevent 1 additional negative event (or to promote 1 additional positive event); this is calculated as 1/absolute risk reduction (rounded to the next whole number), accompanied by the 95% confidence interval.

Odds ratio (OR): describes the odds of a patient in the experimental group having an event divided by the odds of a patient in the control group having the event or the odds that a patient with a certain outcome (eg, MI) was exposed to a given risk factor divided by the odds that a patient without the outcome was exposed to the risk factor.

Open coding¹: first level of coding in a grounded theory study, consisting of basic descriptive coding of narrative content.

Positive predictive value: a measure of the performance of a diagnostic test; it is the proportion of participants with positive test results who actually have the disease or condition being evaluated.

Purposeful (purposive) sampling¹: a type of non-probability sampling in which the researcher selects subjects on the basis of personal judgment about which ones will be most representative of a specific population.

Relative benefit increase (RBI): the proportional increase in the rates of good events between experimental and control participants; it is reported as a percentage (%).

Relative risk reduction (RRR): the proportional reduction in bad outcomes between experimental and control participants; it is reported as a percentage (%).

Sensitivity⁵: a measure of a diagnostic test's ability to correctly detect a disorder when it is present in a sample of people.

Specificity⁵: a measure of a diagnostic test's ability to correctly identify the absence of a disorder in a sample of people who do not have the disorder.