Summary of a study, which may be published alone or as an introduction to a full scientific paper.

A flow chart of the clinical decision pathway described in the guideline, where decision points are represented with boxes, linked with arrows.

The process used to prevent advance knowledge of group assignment in a RCT. The allocation process should be impervious to any influence by the individual making the allocation, by being administered by someone who is not responsible for recruiting participants.

The degree to which the results of an observation, study or review are likely to hold true in a particular clinical practice setting.

Sub-section of individuals within a study who receive one particular intervention, for example placebo arm

Statistical relationship between two or more events, characteristics or other variables. The relationship may or may not be causal.

The initial set of measurements at the beginning of a study (after run-in period where applicable), with which subsequent results are compared.

A study that investigates the effects of an intervention by measuring particular characteristics of a population both before and after taking the intervention, and assessing any change that occurs.

Systematic (as opposed to random) deviation of the results of a study from the ‘true’ results that is caused by the way the study is designed or conducted.

Bivariate data, that shows the relationship between two variables

Keeping the study participants, caregivers, researchers and outcome assessors unaware about the interventions to which the participants have been allocated in a study.

Someone other than a health professional who is involved in caring for a person with a medical condition.

Comparative observational study in which the investigator selects individuals who have experienced an event (For example, developed a disease) and others who have not (controls), and then collects data to determine previous exposure to a possible cause.

Report of a number of cases of a given disease, usually covering the course of the disease and the response to treatment. There is no comparison (control) group of patients.

The extent to which an intervention produces an overall health benefit in routine clinical practice.

The extent to which an intervention is active when studied under controlled research conditions.

A healthcare professional providing direct patient care, for example doctor, nurse or physiotherapist.

The Cochrane Library consists of a regularly updated collection of evidence-based medicine databases including the Cochrane Database of Systematic Reviews (reviews of randomised controlled trials prepared by the Cochrane Collaboration).

A retrospective or prospective follow-up study. Groups of individuals to be followed up are defined on the basis of presence or absence of exposure to a suspected risk factor or intervention. A cohort study can be comparative, in which case two or more groups are selected on the basis of differences in their exposure to the agent of interest.

Co-existence of more than one disease or an additional disease (other than that being studied or treated) in an individual.

Similarity of the groups in characteristics likely to affect the study results (such as health status or age).

This is a recent term whose meaning has changed. It was initially applied to the consultation process in which doctor and patient agree therapeutic decisions that incorporate their respective views, but now includes patient support in medicine taking as well as prescribing communication. Concordance reflects social values but does not address medicine-taking and may not lead to improved adherence.

A range of values for an unknown population parameter with a stated ‘confidence’ (conventionally 95%) that it contains the true value. The interval is calculated from sample data, and generally straddles the sample estimate. The ‘confidence’ value means that if the method used to calculate the interval is repeated many times, then that proportion of intervals will actually contain the true value.

In a study, confounding occurs when the effect of an intervention on an outcome is distorted as a result of an association between the population or intervention or outcome and another factor (the ‘confounding variable’) that can influence the outcome independently of the intervention under study.

Techniques that aim to reach an agreement on a particular issue. Consensus methods may used when there is a lack of strong evidence on a particular topic.

A group of patients recruited into a study that receives no treatment, a treatment of known effect, or a placebo (dummy treatment) - in order to provide a comparison for a group receiving an experimental treatment, such as a new drug.

A type of economic evaluation where both costs and benefits of healthcare treatment are measured in the same monetary units. If benefits exceed costs, the evaluation would recommend providing the treatment.

A type of economic evaluation where various health outcomes are reported in addition to cost for each intervention, but there is no overall measure of health gain.

An economic study design in which consequences of different interventions are measured using a single outcome, usually in ‘natural’ units (For example, life-years gained, deaths avoided, heart attacks avoided, cases detected). Alternative interventions are then compared in terms of cost per unit of effectiveness.

An explicit mathematical framework, which is used to represent clinical decision problems and incorporate evidence from a variety of sources in order to estimate the costs and health outcomes.

A form of cost-effectiveness analysis in which the units of effectiveness are quality-adjusted life-years (QALYs).

Method for investigating the effect of several variables upon the time a specified event takes to happen. The method does not assume any particular “survival model” but it is not truly non-parametric because it does assume that the effects of the predictor variables upon survival are constant over time and are additive in one scale.

The Bayesian equivalent of a confidence interval.

An explicit quantitative approach to decision making under uncertainty, based on evidence from research. This evidence is translated into probabilities, and then into diagrams or decision trees which direct the clinician through a succession of possible scenarios, actions and outcomes.

Costs and perhaps benefits incurred today have a higher value than costs and benefits occurring in the future. Discounting health benefits reflects individual preference for benefits to be experienced in the present rather than the future. Discounting costs reflects individual preference for costs to be experienced in the future rather than the present.

An intervention is said to be dominated if there is an alternative intervention that is both less costly and more effective.

A participant who withdraws from a trial before the end.

Comparative analysis of alternative health strategies (interventions or programmes) in terms of both their costs and consequences.

The observed association between interventions and outcomes or a statistic to summarise the strength of the observed association.

See ‘Clinical effectiveness’.

See ‘Clinical efficacy’.

The study of a disease within a population, defining its incidence and prevalence and examining the roles of external influences (For example, infection, diet) and interventions.

A standardise instrument used to measure a health outcome. It provides a single index value for health status.

Information on which a decision or guidance is based. Evidence is obtained from a range of sources including randomised controlled trials, observational studies, expert opinion (of clinical professionals and/or patients).

Criteria that define who is not eligible to participate in a clinical study.

Explicit standards used to decide which studies should be excluded from consideration as potential sources of evidence.

If Option A is both more clinically effective than Option B and has a lower cost per unit of effect, when both are compared with a do-nothing alternative then Option A is said to have extended dominance over Option B. Option A is therefore more efficient and should be preferred, other things remaining equal.

In data analysis, predicting the value of a parameter outside the range of observed values.

Observation over a period of time of an individual, group or initially defined population whose appropriate characteristics have been assessed in order to observe changes in health status or health-related variables.

The extent to which the results of a study based on measurement in a particular patient population and/or a specific context hold true for another population and/or in a different context. In this instance, this is the degree to which the guideline recommendation is applicable across both geographical and contextual settings. For instance, guidelines that suggest substituting one form of labour for another should acknowledge that these costs might vary across the country.

See ‘Reference standard’GRADE.

GRADE / GRADE profile A system developed by the GRADE Working Group to address the shortcomings of present grading systems in healthcare. The GRADE system uses a common, sensible and transparent approach to grading the quality of evidence. The results of applying the GRADE system to clinical trial data are displayed in a table known as a GRADE profile.

Adverse effects of an intervention.

The study of the allocation of scarce resources among alternative healthcare treatments. Health economists are concerned with both increasing the average level of health in the population and improving the distribution of health.

A grouping consisting of patient events that have been judged to consume a similar level of resource

A combination of an individual’s physical, mental and social well-being; not merely the absence of disease.

The term is used in meta-analyses and systematic reviews when the results or estimates of effects of treatment from separate studies seem to be very different – in terms of the size of treatment effects or even to the extent that some indicate beneficial and others suggest adverse treatment effects. Such results may occur as a result of differences between studies in terms of the patient populations, outcome measures, definition of variables or duration of follow-up.

Results are imprecise when studies include relatively few patients and few events and thus have wide confidence intervals around the estimate of effect.

Explicit criteria used to decide which studies should be considered as potential sources of evidence.

The analysis of additional costs and additional clinical outcomes with different interventions.

The mean cost per patient associated with an intervention minus the mean cost per patient associated with a comparator intervention.

The difference in the mean costs in the population of interest divided by the differences in the mean outcomes in the population of interest for one treatment compared with another.

The value (usually in monetary terms) of an intervention net of its cost compared with a comparator intervention. The INB can be calculated for a given cost-effectiveness (willingness to pay) threshold. If the threshold is £20,000 per QALY gained then the INB is calculated as: (£20,000 × QALYs gained) − Incremental cost.

The available evidence is different to the review question being addressed, in terms of PICO (population, intervention, comparison and outcome).

A strategy for analysing data from a randomised controlled trial. All participants are included in the arm to which they were allocated, whether or not they received (or completed) the intervention given to that arm. Intention-to-treat analysis prevents bias caused by the loss of participants, which may disrupt the baseline equivalence established by randomisation and which may reflect non-adherence to the protocol.

Measure in quantitative studies, where it ensures that a researcher’s experiment design closely follows the principle of cause and effect.

Healthcare action intended to benefit the patient, for example, drug treatment, surgical procedure, psychological therapy.

The period of time during a surgical procedure.

A statistical measure of inter-rater agreement that takes into account the agreement occurring by chance.

The total number of days a participant stays in hospital.

See ‘Product licence’.

Mean average years of life gained per person as a result of the intervention compared with an alternative intervention.

The likelihood ratio combines information about the sensitivity and specificity. It tells you how much a positive or negative result changes the likelihood that a patient would have the disease. The likelihood ratio of a positive test result (LR+) is sensitivity divided by 1- specificity.

Residential care in a home that may include skilled nursing care and help with everyday activities. This includes nursing homes and residential homes.

This represents the number of participants in a study who were not available for follow-up measurements after an intervention. Loss to follow up can create bias if two groups have a differential percentage of loss to follow up, and bias can also be created between groups through a breakdown of randomisation.

A method for estimating long-term costs and effects for recurrent or chronic conditions, based on health states and the probability of transition between them within a given time period (cycle).

A statistical technique for combining (pooling) the results of a number of studies that address the same question and report on the same outcomes to produce a summary result. The aim is to derive more precise and clear information from a large data pool. It is generally more reliably likely to confirm or refute a hypothesis than the individual trials.

A statistical model for analysis of the relationship between two or more predictor (independent) variables and the outcome (dependent) variable.

A measure of the usefulness of a screening/diagnostic test. It is the proportion of those with a negative test result who do not have the disease, and can be interpreted as the probability that a negative test result is correct.

The value (usually in monetary terms) of an intervention net of its cost. The NMB can be calculated for a given cost-effectiveness (willingness to pay) threshold. If the threshold is £20,000 per QALY gained then the NMB is calculated as: (£20,000 × QALYs gained) – cost. This value can then be compared easily against other interventions.

The number of patients that who on average must be treated to prevent a single occurrence of the outcome of interest.

Retrospective or prospective study in which the investigator observes the natural course of events with or without control groups; for example, cohort studies and case control studies.

A measure of treatment effectiveness. The odds of an event happening in the treatment group, expressed as a proportion of the odds of it happening in the control group. The ‘odds’ is the ratio of events to non-events.

The loss of other health care programmes displaced by investment in or introduction of another intervention. This may be best measured by the health benefits that could have been achieved had the money been spent on the next best alternative healthcare intervention.

Measure of the possible results that may stem from exposure to a preventive or therapeutic intervention. Outcome measures may be intermediate endpoints or they can be final endpoints. See ‘Intermediate outcome’.

The period from admission through surgery until discharge, encompassing the pre-operative and post-operative periods.

An inactive and physically identical medication or procedure used as a comparator in controlled clinical trials.

The use or prescription of multiple medications.

In screening/diagnostic tests: A measure of the usefulness of a screening/diagnostic test. It is the proportion of those with a positive test result who have the disease, and can be interpreted as the probability that a positive test result is correct.

Pertaining to the period after patients leave the operating theatre, following surgery.

For diagnostic tests. The proportion of patients with that particular test result who have the target disorder (post test odds/[1 + post-test odds]).

The ability to demonstrate an association when one exists. Power is related to sample size; the larger the sample size, the greater the power and the lower the risk that a possible association could be missed.

The period before surgery commences.

For diagnostic tests. The proportion of people with the target disorder in the population at risk at a specific time point or time interval. Prevalence may depend on how a disorder is diagnosed.

Healthcare delivered to patients outside hospitals. Primary care covers a range of services provided by general practitioners, nurses, dentists, pharmacists, opticians and other healthcare professionals.

The outcome of greatest importance, usually the one in a study that the power calculation is based on.

An authorisation from the MHRA to market a medicinal product.

A probable course or outcome of a disease. Prognostic factors are patient or disease characteristics that influence the course. Good prognosis is associated with low rate of undesirable outcomes; poor prognosis is associated with a high rate of undesirable outcomes.

A study in which people are entered into the research and then followed up over a period of time with future events recorded as they happen. This contrasts with studies that are retrospective.

Also known as reporting bias. A bias caused by only a subset of all the relevant data being available. The publication of research can depend on the nature and direction of the study results. Studies in which an intervention is not found to be effective are sometimes not published. Because of this, systematic reviews that fail to include unpublished studies may overestimate the true effect of an intervention. In addition, a published report might present a biased set of results (e.g. only outcomes or sub-groups where a statistically significant difference was found.

The probability that an observed difference could have occurred by chance, assuming that there is in fact no underlying difference between the means of the observations. If the probability is less than 1 in 20, the P value is less than 0.05; a result with a P value of less than 0.05 is conventionally considered to be ‘statistically significant’.

See ‘Health-related quality of life’.

An index of survival that is adjusted to account for the patient’s quality of life during this time. QALYs have the advantage of incorporating changes in both quantity (longevity/mortality) and quality (morbidity, psychological, functional, social and other factors) of life. Used to measure benefits in cost-utility analysis. The QALYs gained are the mean QALYs associated with one treatment minus the mean QALYs associated with an alternative treatment.

An abridged version of NICE guidance, which presents the key priorities for implementation and summarises the recommendations for the core clinical audience.

Allocation of participants in a research study to two or more alternative groups using a chance procedure, such as computer-generated random numbers. This approach is used in an attempt to ensure there is an even distribution of participants with different characteristics between groups and thus reduce sources of bias.

A comparative study in which participants are randomly allocated to intervention and control groups and followed up to examine differences in outcomes between the groups.

See ‘Randomised controlled trial’.

A graphical method of assessing the accuracy of a diagnostic test. Sensitivity Is plotted against 1-specificity. A perfect test will have a positive, vertical linear slope starting at the origin. A good test will be somewhere close to this ideal.

The test that is considered to be the best available method to establish the presence or absence of the outcome – this may not be the one that is routinely used in practice.

The number of times more likely or less likely an event is to happen in one group compared with another (calculated as the risk of the event in group A/the risk of the event in group B).

See publication bias.

The likely impact in terms of finance, workforce or other NHS resources.

A retrospective study deals with the present/ past and does not involve studying future events. This contrasts with studies that are prospective.

In guideline development, this term refers to the questions about treatment and care that are formulated to guide the development of evidence-based recommendations.

An outcome used to evaluate additional effects of the intervention deemed a priori as being less important than the primary outcomes.

A systematic bias in selecting participants for study groups, so that the groups have differences in prognosis and/or therapeutic sensitivities at baseline. Randomisation (with concealed allocation) of patients protects against this bias.

Sensitivity or recall rate is the proportion of true positives which are correctly identified as such. For example in diagnostic testing it is the proportion of true cases that the test detects. See the related term ‘Specificity’

A means of representing uncertainty in the results of economic evaluations. Uncertainty may arise from missing data, imprecise estimates or methodological controversy. Sensitivity analysis also allows for exploring the generalisability of results to other settings. The analysis is repeated using different assumptions to examine the effect on the results.

One-way simple sensitivity analysis (univariate analysis): each parameter is varied individually in order to isolate the consequences of each parameter on the results of the study.

Multi-way simple sensitivity analysis (scenario analysis): two or more parameters are varied at the same time and the overall effect on the results is evaluated.

Threshold sensitivity analysis: the critical value of parameters above or below which the conclusions of the study will change are identified.

Probabilistic sensitivity analysis: probability distributions are assigned to the uncertain parameters and are incorporated into evaluation models based on decision analytical techniques (For example, Monte Carlo simulation).

A standardise instrument used to measure a health outcome. It provides a single index value for health status.

A result is deemed statistically significant if the probability of the result occurring by chance is less than 1 in 20 (p <0.05).

The proportion of true negatives that a correctly identified as such. For example in diagnostic testing the specificity is the proportion of non-cases incorrectly diagnosed as cases.

See related term ‘Sensitivity’.

In terms of literature searching a highly specific search is generally narrow and aimed at picking up the key papers in a field and avoiding a wide range of papers.

Those with an interest in the use of the guideline. Stakeholders include manufacturers, sponsors, healthcare professionals, and patient and carer groups.

Research that summarises the evidence on a clearly formulated question according to a pre-defined protocol using systematic and explicit methods to identify, select and appraise relevant studies, and to extract, collate and report their findings. It may or may not use statistical meta-analysis.

The time span over which costs and health outcomes are considered in a decision analysis or economic evaluation.

Assigning a participant to a particular arm of the trial.

Analysis which separately explores each variable in a data set.

A measure of the strength of an individual’s preference for a specific health state in relation to alternative health states. The utility scale assigns numerical values on a scale from 0 (death) to 1 (optimal or ‘perfect’ health). Health states can be considered worse than death and thus have a negative value.