HTA and HEOR glossary

A

All Wales Medicines Strategy Group (AWMSG)

The body that provides health technology assessment advice on medicines for NHS Wales, supported by the All Wales Therapeutics and Toxicology Centre. AWMSG assesses licensed medicines that are not in NICE's work programme, or where an early Welsh assessment would be beneficial; most licensed medicines are expected to be assessed by NICE. Where NICE later issues guidance for the same medicine and indication, it usually supersedes AWMSG advice, and recommendations are ratified by the Welsh Government.

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AMCP dossier

A product dossier prepared to the Academy of Managed Care Pharmacy (AMCP) Format for Formulary Submissions, which gives manufacturers guidance on presenting clinical and economic evidence to US health care decision makers. The Format is advisory rather than mandatory, and the dossier is intended as a living document across the product life cycle, from pre-approval to post-approval. AMCP released Format 6.0 in October 2026, adding guidance for cell and gene therapies and biosimilars.

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Anchored indirect comparison

An indirect comparison of two treatments that is made through a common comparator arm shared by the trials, so that the relative effect within each trial, and therefore its randomisation, is preserved. Both the HTA Coordination Group and NICE Decision Support Unit guidance state that anchored comparisons should always be preferred to unanchored methods in a connected network. Examples include the Bucher method, network meta-analysis and anchored population-adjusted methods.

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B

Bucher method

The adjusted indirect comparison described by Bucher and colleagues in 1997, in which the relative effect of A versus C is estimated from trials of A versus B and C versus B, for example log HR(AC) = log HR(AB) − log HR(CB), with the variances summed. It preserves randomisation within trials but widens uncertainty. The HTA Coordination Group guideline notes that it can only be used in simple star networks, where consistency cannot be tested.

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Budget impact analysis

An estimate of the change in expenditure for a specific budget holder if a new technology is adopted, usually over three to five years and accounting for eligible population size, uptake, displacement of current treatments and associated costs. Unlike cost-effectiveness analysis, it addresses affordability rather than value for money. In England, NICE and NHS England apply a budget impact test, which the NICE manual set at £40 million in June 2025.

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C

Canada's Drug Agency (CDA-AMC)

The pan-Canadian HTA organisation formerly known as CADTH, which adopted its new name on 1 May 2024. It conducts reimbursement reviews of drugs and other technologies and issues recommendations to participating public drug plans. Its expanded mandate includes promoting appropriate use of medicines and improving access to pan-Canadian data, including real-world evidence.

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Cancer Drugs Fund (CDF)

An NHS England fund that pays for cancer medicines that NICE has recommended for use within managed access while further data are collected to resolve clinical uncertainty. At the end of the managed access period NICE reviews the evidence and decides on routine commissioning. NHS England states that the CDF has a ring-fenced budget of £340 million, alongside the Innovative Medicines Fund for non-cancer medicines.

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Comparator

The treatment, or set of treatments, against which a new technology is assessed. At NICE, comparators are technologies that represent established NHS practice, and technologies recommended within managed access are not considered suitable comparators. In the EU joint clinical assessment, comparators are defined PICO by PICO from Member State requirements and may include an individualised treatment comparator.

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Cost-comparison analysis

A NICE evaluation route for technologies likely to provide similar or greater health benefits at similar or lower cost than relevant comparators. The analysis compares the costs and resource use of the technology with those of the comparator rather than estimating QALYs. For medicines, relevant comparators are those already recommended in published NICE guidance for the same population.

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Cost-effectiveness acceptability curve (CEAC)

A graph, derived from probabilistic sensitivity analysis, showing the probability that each option is cost-effective across a range of values of the cost-effectiveness threshold. It summarises decision uncertainty rather than the size of the expected net benefit. The option with the highest expected net benefit at a given threshold is not always the one with the highest probability of being cost-effective, so CEACs are usually read alongside expected net benefit.

Cost-effectiveness analysis (CEA)

A comparative economic evaluation in which costs are related to a single measure of health effect, such as life-years gained or events avoided, and summarised as an incremental cost per unit of effect. The term is also used broadly to include cost-utility analysis. Natural-unit CEA allows comparison within a disease area but not across them, which is why most HTA agencies prefer cost-utility analysis for reimbursement decisions.

Cost-effectiveness threshold

The maximum cost per unit of health gain, usually per QALY, at which a decision maker considers a technology to be good value, reflecting the health forgone elsewhere in the system. Since its March 2026 manual update, NICE normally recommends technologies with a most plausible ICER below £25,000 per QALY, and between £25,000 and £35,000 makes explicit reference to factors such as uncertainty and uncaptured benefits; the level for highly specialised technologies is £100,000 per QALY. Thresholds differ between countries, and some systems do not publish one.

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Cost-minimisation analysis

An economic evaluation that compares only costs, on the premise that the outcomes of the alternatives are equivalent. Its validity depends on robust evidence of equivalence, not merely a lack of evidence of difference. In practice, agencies such as NICE use structured cost-comparison routes with explicit criteria for when similar effectiveness can be assumed.

Cost-utility analysis (CUA)

A form of cost-effectiveness analysis in which health effects are measured in quality-adjusted life years (QALYs), allowing comparison across diseases. Results are expressed as an incremental cost per QALY gained or as net benefit. It is the reference-case method for NICE technology appraisals and for HIQA's national guidelines in Ireland.

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D

Deterministic sensitivity analysis (DSA)

An analysis in which one or more model inputs are varied over plausible ranges, while others are held at base-case values, to see how results change. One-way DSA is often presented as a tornado diagram. It identifies influential parameters but does not quantify joint parameter uncertainty, which is the role of probabilistic sensitivity analysis.

Discounting

The adjustment of future costs and health effects to present values, reflecting time preference, using PV = X / (1 + r)^t. NICE's reference case discounts costs and health effects at 3.5% a year, with 1.5% accepted for alternative analyses in specific circumstances. HIQA's 2025 Irish guidelines use 4% a year for both costs and outcomes.

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Discrete event simulation (DES)

An individual-level modelling technique in which simulated patients move through time according to the timing of events, drawn from time-to-event distributions, rather than in fixed cycles. It handles competing events, resource constraints, queues and patient history flexibly. The NICE Decision Support Unit covers patient-level simulation in Technical Support Document 15.

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Dominance and extended dominance

An option is dominated when another option is both less costly and more effective. It is extendedly dominated when a combination of two other options would deliver more health at the same or lower cost, which is shown by a higher ICER than the next more effective option. Dominated and extendedly dominated options are removed before calculating incremental cost-effectiveness ratios in a fully incremental analysis.

E

Early dialogue and joint scientific consultation (JSC)

Early dialogue is scientific advice from HTA bodies, sometimes in parallel with regulators, on a developer's evidence generation plans before pivotal studies start. Under the EU HTA Regulation, joint scientific consultations allow developers to obtain advice during study planning so that evidence meets the needs of a later joint clinical assessment. Requests can only be submitted in the request periods published in the HTA Coordination Group's annual work programme.

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Effect modifier

A characteristic that changes the relative effect of a treatment, on a given scale, between subgroups of patients. Imbalance in effect modifiers between trials is the main threat to the validity of anchored indirect comparisons. NICE Decision Support Unit recommendations state that unanchored comparisons must also adjust for all prognostic variables, because they rely on predicting absolute outcomes.

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Effective sample size (ESS)

In a weighted analysis such as a matching-adjusted indirect comparison, the number of unweighted patients that would give the same precision, calculated as ESS = (sum of weights)^2 / sum of squared weights. A large fall from the original sample indicates poor overlap between populations and that a few patients dominate the estimate. It is routinely reported alongside population-adjusted comparisons.

EQ-5D

A generic, preference-based measure of health-related quality of life covering mobility, self-care, usual activities, pain or discomfort, and anxiety or depression, available in three-level (3L) and five-level (5L) versions. A value set converts responses into utilities for QALY calculations. In its interim methods statement of 27 August 2026, NICE made the EQ-5D-5L and the new UK value set its preferred approach for adults, applied to topics starting after publication.

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EUnetHTA

The European Network for Health Technology Assessment, a collaboration of European HTA bodies that developed joint methods, assessments and early dialogues through successive EU-funded joint actions and the EUnetHTA 21 service contract. Its methodological work informed the guidance now adopted by the HTA Coordination Group. Joint clinical assessments are now carried out under Regulation (EU) 2021/2282 rather than through EUnetHTA.

Expected value of perfect information (EVPI)

A value of information measure equal to the expected net benefit with perfect information minus the expected net benefit of the decision under current information, calculated from probabilistic analysis. Multiplied by the size of the affected population over the decision's lifetime, it gives an upper bound on the value of further research. Expected value of partial perfect information (EVPPI) applies the same logic to specific parameters to show where research would be most valuable.

External control arm

A comparator group built from data outside the trial, such as registries, electronic health records or historical trials, typically used when the pivotal study is single-arm. Comparisons with external controls are non-randomised and require methods such as propensity score weighting with demonstrated overlap and balance. The HTA Coordination Group guidance notes that single-arm or non-randomised evidence usually threatens internal validity and calls for sensitivity analyses and clear caveats.

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G

G-BA (Federal Joint Committee)

The Gemeinsamer Bundesausschuss, Germany's highest decision-making body of the joint self-government in statutory health insurance, which conducts the early benefit assessment of new medicines under section 35a of Social Code Book V (AMNOG). Manufacturers submit a dossier demonstrating added benefit over the appropriate comparator therapy set by the G-BA, results are published within three months, and the G-BA passes its resolution after a further three months. The resolution informs price negotiation with the statutory health insurance funds.

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Global value dossier (GVD)

A company's core reference document that sets out the disease burden, unmet need, clinical evidence, economic case and value messages for a product, used as the source for local adaptations. It is an internal tool rather than a submission format, and affiliates tailor its content to national HTA and payer requirements. A well-governed GVD keeps the evidence base consistent across markets.

GRADE

The Grading of Recommendations Assessment, Development and Evaluation approach, which rates the certainty of a body of evidence for each outcome as high, moderate, low or very low, considering risk of bias, inconsistency, indirectness, imprecision and publication bias. It is widely used in guidelines and systematic reviews. The HTA Coordination Group's validity guidance maps several GRADE domains to its own concepts but does not require GRADE.

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H

HAS (Haute Autorité de Santé)

France's independent public health authority. Its Transparency Committee appraises medicines using two scores: the clinical benefit (SMR), which informs whether and at what rate a medicine is reimbursed, and the clinical added value (ASMR), which is used in pricing negotiations. Its Economic and Public Health Evaluation Committee (CEESP) issues efficiency opinions, for example where a high ASMR (I to III) is claimed and expected second-year sales reach €20 million.

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Health economics and outcomes research (HEOR)

The disciplines that generate and analyse evidence on the costs, outcomes and value of health interventions, including economic modelling, evidence synthesis, real-world evidence, patient-reported outcomes and health-related quality of life. HEOR provides much of the evidence used in HTA submissions and payer negotiations. In industry it typically sits alongside market access and medical affairs.

Health technology assessment (HTA)

A multidisciplinary process that uses explicit methods to determine the value of a health technology at different points in its life cycle, to inform decision making about its use and funding. It typically covers clinical effectiveness and safety and may include cost-effectiveness, budget impact, and ethical, organisational, social and legal aspects. Under the EU HTA Regulation, the joint European assessment covers only the clinical domains.

Highly specialised technologies (HST)

NICE's programme for evaluating technologies for very rare, severe conditions, with its own decision rules. The normal level for highly specialised technologies is £100,000 per QALY, and a QALY weight between 1 and 3 can be applied where lifetime incremental QALY gains per patient are between 10 and 30 or more. The 2026 threshold change for technology appraisals did not alter the HST level.

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HIQA

The Health Information and Quality Authority, Ireland's independent authority for health and social care quality, which also conducts HTAs and publishes national HTA methods guidelines. Its 2025 economic evaluation guidelines specify cost-utility analysis as the preferred reference case, a publicly funded health and social care perspective for costs, and a 4% annual discount rate for costs and outcomes. Drug reimbursement assessments in Ireland are carried out by the NCPE.

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HTA Coordination Group (HTACG)

The Member State Coordination Group on HTA established by Regulation (EU) 2021/2282, made up of representatives of national HTA authorities and bodies. It oversees joint clinical assessments and joint scientific consultations, endorses JCA reports and adopts methodological and procedural guidance. Its subgroups, including the JCA subgroup, carry out the operational work.

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HTA Regulation (EU HTAR)

Regulation (EU) 2021/2282, which established joint clinical assessments, joint scientific consultations, identification of emerging technologies and voluntary cooperation on HTA across the EU. It has applied since 12 January 2025 to oncology medicines with new active substances and advanced therapy medicinal products, and extends to designated orphan medicines from 13 January 2028 and to other medicines in scope from 13 January 2030. Member States must give due consideration to published JCA reports and should not request at national level information already submitted.

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I

Incremental cost-effectiveness ratio (ICER)

The difference in mean costs between two options divided by the difference in mean health effects, for example ICER = (C1 − C0) / (QALY1 − QALY0). In a fully incremental analysis, options are ranked by effectiveness and dominated or extendedly dominated options are removed before ICERs are calculated. The ICER is compared with a cost-effectiveness threshold; it is undefined or misleading when effect differences are close to zero, where net benefit is more informative.

Individualised treatment comparator

A comparator in the EU joint clinical assessment that bundles two or more treatment options, chosen for each patient according to their characteristics, into a single comparison. It is used when a population cannot be split into a limited number of meaningful subpopulations, and yields one effect estimate per outcome against the combined options. Under the HTA Coordination Group scoping guidance it cannot be merged with other comparator scenarios and so forms a separate PICO.

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Innovative Medicines Fund (IMF)

An NHS England fund, launched in June 2022, that provides a managed access route for promising non-cancer medicines recommended by NICE for use while further data are collected. Only the eligible population recommended by NICE receives IMF-funded treatment. It operates alongside the Cancer Drugs Fund, with the two funds together having £680 million of ring-fenced funding.

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International reference pricing (IRP)

A pricing policy in which a country sets or negotiates the price of a medicine by reference to its prices in a defined basket of other countries, often using the lowest or an average price. It is widely used in Europe and creates interdependence between national prices, which influences launch sequencing and the use of confidential discounts. Most-favoured-nation proposals in the United States apply a similar logic.

IQWiG

The Institute for Quality and Efficiency in Health Care, Germany's independent scientific institute that assesses the benefits and harms of medical interventions. The G-BA can commission IQWiG to carry out the dossier assessment in the early benefit assessment of new medicines, and IQWiG publishes its own General Methods. It also acts as an assessor or co-assessor in EU joint clinical assessments.

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J

Joint clinical assessment (JCA)

An EU-level assessment under Regulation (EU) 2021/2282 that describes the relative effectiveness and safety of a health technology, and the certainty of those effects, for each PICO in the agreed scope. The report "shall not contain any value judgement or conclusions on the overall clinical added value"; pricing, reimbursement and economic evaluation remain national. For medicines, the developer must submit the dossier within 100 days of the Commission's first request under Implementing Regulation (EU) 2024/1381.

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L

Living systematic review

A systematic review that is continually updated, with searches run at defined intervals and new evidence incorporated as it becomes available. It suits fast-moving fields and evidence programmes that must support several submissions over time. Its feasibility depends on a stable protocol, efficient screening workflows and clear rules for when analyses are re-run.

M

Managed access

A NICE recommendation route in which a promising technology is funded for a defined period while further evidence is collected to resolve key uncertainties, after which NICE decides on routine use. A managed access agreement includes a data collection agreement, lasting no more than five years, and a commercial access agreement with NHS England. Medicines in managed access are funded through the Cancer Drugs Fund or the Innovative Medicines Fund.

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Mapping

The estimation of utility values from a non-preference-based measure, or from one version of a preference-based measure to another, using a statistical model fitted to data where both are collected. NICE requires specific mapping approaches, for example the Decision Support Unit model when mapping EQ-5D-3L data to the EQ-5D-5L UK value set. The NICE Decision Support Unit covers mapping methods in Technical Support Document 22, updated in September 2026.

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Markov model

A state-transition cohort model in which a hypothetical population moves between mutually exclusive health states in discrete cycles according to transition probabilities, accumulating costs and QALYs in each state. The basic model is memoryless, so history-dependent processes need additional tunnel states or a different structure. Half-cycle or similar corrections are applied to account for transitions occurring within cycles.

Matching-adjusted indirect comparison (MAIC)

A population-adjusted indirect comparison in which individual patient data from one trial are reweighted, using method-of-moments propensity score weights, so that the distribution of selected covariates matches the published aggregate data of another trial. It can be anchored, through a common comparator, or unanchored. Guidance from the HTA Coordination Group and NICE Decision Support Unit requires sufficient population overlap and prespecified covariates, and regards unanchored MAIC as relying on very strong assumptions.

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Microsimulation

An individual-level state-transition model in which patients are simulated one at a time, allowing transition probabilities to depend on individual characteristics and history. It avoids the memoryless limitation of cohort Markov models at the cost of more computation and Monte Carlo error. Enough simulated individuals are needed for stable results, particularly within probabilistic analysis.

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Mixture cure model

A survival model that assumes a fraction of patients is cured, experiencing background mortality only, while the remainder follow a parametric survival distribution. It is used where long-term survival plateaus are clinically plausible, for example with some immunotherapies and cell therapies. The estimated cure fraction is highly sensitive to follow-up length and should be supported by external evidence; the NICE Decision Support Unit discusses it among flexible survival methods.

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Most-favoured-nation (MFN) pricing

A pricing approach in which a buyer seeks a price no higher than the lowest price paid in a set of comparable countries. In the United States, Executive Order 14297 of 12 May 2025 directed the administration to communicate MFN price targets to manufacturers, to bring prices in line with comparably developed nations. MFN policies increase the importance of international price relationships for launch and pricing strategy.

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Multilevel network meta-regression (ML-NMR)

A population-adjustment method that extends network meta-analysis to combine individual patient data and aggregate data across a whole network, by integrating an individual-level regression model over the covariate distribution of aggregate-data studies. It can produce estimates for any target population and maintains coherence across the network. The HTA Coordination Group guideline notes that, as currently proposed, it requires substantial individual patient data and cannot be applied to time-to-event data.

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N

National Centre for Pharmacoeconomics (NCPE)

The Irish body that assesses medicines for reimbursement on behalf of the Health Service Executive (HSE). All applications begin with a rapid review of about four weeks, after which selected medicines undergo a full HTA of clinical and cost-effectiveness and budget impact, taking about 18 weeks plus stop-clock time. NCPE recommendations are advisory, with final decisions made by the HSE, and the NCPE also acts as an assessor in EU joint clinical assessments.

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Net monetary benefit (NMB) and net health benefit (NHB)

Measures that convert cost-effectiveness results into a single value at a given threshold λ: NMB = λ × ΔQALY − ΔCost and NHB = ΔQALY − ΔCost / λ. A positive value indicates that the technology is cost-effective at that threshold. NICE asks for net health benefit to be presented at £25,000 and £35,000 per QALY, with and without any QALY weighting.

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Network meta-analysis (NMA)

A statistical synthesis of a connected network of trials that combines direct and indirect evidence to estimate relative effects between all treatments in the network, in a frequentist or Bayesian framework. It assumes similarity, homogeneity and consistency, and consistency can only be checked where closed loops exist. NICE asks for an NMA where technologies have not been compared in a single trial, using the methods in its Decision Support Unit evidence synthesis series.

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NICE

The National Institute for Health and Care Excellence, which produces evidence-based guidance for health and care in England, including technology appraisals of medicines and other health technologies. Its methods and processes are set out in its health technology evaluation manual (PMG36), which uses cost-utility analysis as the reference case. NICE technology appraisal recommendations carry a statutory funding requirement for the NHS in England.

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P

Partitioned survival model

A model, common in oncology, in which the proportion of patients in each health state over time is derived directly from survival curves, typically progression-free and overall survival, with progressed disease taken as the difference. It does not model transitions explicitly, so it assumes no structural link between endpoints. The NICE Decision Support Unit describes its strengths and limitations in Technical Support Document 19.

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Patient access scheme (PAS)

A pricing agreement proposed by a company to improve the cost-effectiveness of a medicine in England, considered alongside NICE appraisal. A simple discount PAS gives a confidential fixed or percentage discount on the list price and is the preferred form; complex schemes, such as outcome-based or dose-capped arrangements, are non-confidential and involve a fuller review. NHS England makes the final decision on schemes after NICE's review.

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PICO

A framework that defines a research or decision question by Population, Intervention, Comparator and Outcomes, used to structure systematic reviews and HTA scopes. In the EU joint clinical assessment, the assessment scope is expressed as a set of PICOs consolidated from Member State needs, with the aim of translating those needs into the lowest possible number of PICOs. Each PICO requires its own relative effect estimates in the developer's dossier.

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PRISMA

The Preferred Reporting Items for Systematic reviews and Meta-Analyses, a reporting guideline whose current version, PRISMA 2020, provides a checklist and a flow diagram showing records identified, screened, excluded and included. It governs how a review is reported, not how it is conducted. Extensions cover network meta-analyses, scoping reviews and literature searches.

Probabilistic sensitivity analysis (PSA)

An analysis in which all uncertain model inputs are assigned probability distributions and sampled simultaneously, typically over thousands of iterations, to estimate expected costs and outcomes and the probability that each option is cost-effective. Results are shown on a cost-effectiveness plane and as acceptability curves. NICE expects the uncertainty in key relationships, such as a surrogate-to-final outcome relationship, to be reflected in the PSA.

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Q

QALY shortfall

NICE's measure of disease severity. Absolute QALY shortfall is the expected remaining QALYs of the general population of the same age and sex minus the expected QALYs with the condition under current treatment; proportional shortfall divides this by the general population's remaining QALYs. Both are discounted at the reference-case rate, and the measure implying greater severity determines the severity weight.

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Quality-adjusted life year (QALY)

A measure of health that combines length and quality of life, calculated by multiplying the time spent in a health state by its utility weight, where 1 represents full health and 0 represents death. One QALY equals one year in full health. NICE's reference case expresses health effects in QALYs and gives an additional QALY the same weight regardless of who receives it, except where decision modifiers apply.

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R

Real-world data (RWD)

Data relating to patient health status or the delivery of care collected outside conventional randomised trials, for example from electronic health records, registries, claims databases and patient-generated sources. Its fitness for purpose depends on provenance, completeness and relevance to the research question. RWD becomes real-world evidence only once it has been analysed to address a defined question.

Real-world evidence (RWE)

Evidence about the use, benefits or harms of a technology derived from the analysis of real-world data. In HTA it is used to characterise natural history, current practice, resource use and long-term outcomes, and sometimes to construct external controls for comparative effectiveness. NICE's manual refers to its real-world evidence framework and states that study appraisal and sensitivity analyses are as important for these data as for trial data.

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Reference case

The set of methods an HTA agency considers most appropriate for its decisions, specified so that submissions are consistent and comparable. NICE's reference case includes a scope-defined decision problem, an NHS and personal social services cost perspective, cost-utility analysis, QALYs measured preferably with the EQ-5D, a time horizon long enough to capture all important differences, and 3.5% discounting. Non-reference-case analyses can be presented but must be justified.

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RoB 2

The revised Cochrane risk-of-bias tool for randomised trials, which assesses bias across five domains: the randomisation process, deviations from intended interventions, missing outcome data, outcome measurement, and selection of the reported result. Judgements are made per outcome or result, leading to low risk, some concerns or high risk. The HTA Coordination Group's validity guidance currently prefers the original Cochrane RoB 1 instrument for joint clinical assessments, so reviews serving several agencies may need both.

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ROBINS-I

The Risk Of Bias In Non-randomised Studies of Interventions tool, which assesses a non-randomised study against a hypothetical target trial across domains including confounding, selection of participants, classification of interventions, deviations, missing data, outcome measurement and selective reporting. Overall judgements range from low to critical risk of bias. The HTA Coordination Group's validity guidance recommends it for non-randomised comparative studies.

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S

Scottish Medicines Consortium (SMC)

The body that advises NHS Scotland on the clinical and cost-effectiveness of newly licensed medicines. For medicines used at the end of life or for rare conditions, the company can request a Patient and Clinician Engagement (PACE) meeting, which gives patient groups and clinicians a stronger voice in SMC decision making. SMC defines end of life as a condition usually leading to death within three years with current treatment.

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Severity modifier

NICE's decision-making modifier that gives greater weight to QALYs gained in severe conditions, based on absolute and proportional QALY shortfall. A weight of 1.2 applies where proportional shortfall is 0.85 to 0.95 or absolute shortfall is 12 to 18, and 1.7 where proportional shortfall is at least 0.95 or absolute shortfall at least 18, using whichever implies greater severity. It replaced the end-of-life modifier in the 2022 manual.

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Simulated treatment comparison (STC)

A population-adjusted indirect comparison that fits an outcome regression model to individual patient data from one trial and uses it to predict outcomes in the population of a comparator trial with only aggregate data. Like MAIC it can be anchored or unanchored. The HTA Coordination Group guideline cautions that, with non-identity link functions, the commonly applied approach can bias both conditional and marginal estimates.

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Surrogate endpoint

An outcome, such as a biomarker or progression-free survival, used in place of a final patient-relevant outcome such as survival or quality of life. NICE recognises three levels of evidence for surrogacy, with level 1 being RCT evidence that treatment effects on the surrogate correspond to effects on the final outcome. The HTA Coordination Group outcomes guidance considers trial-level evidence required for validation and describes a correlation of at least 0.85 as high.

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Systematic literature review (SLR)

A review that uses explicit, prespecified and reproducible methods to identify, select, appraise and synthesise all relevant studies on a defined question, typically with dual independent screening and data extraction. It underpins evidence synthesis for HTA: NICE expects a systematic review using a predefined protocol. The EU joint clinical assessment additionally requires a search cut-off no more than three months before dossier submission.

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Targeted literature review (TLR)

A focused, non-exhaustive literature review designed to answer a specific question quickly, for example to source a model input or describe treatment patterns. It uses structured but limited searches and may not involve dual screening. It is appropriate for context and parameter sourcing, but not where an HTA body expects a systematic review of comparative evidence.

Treatment switching

The situation in which trial patients, usually in the control arm, switch to the experimental treatment or another therapy after progression, which can bias intention-to-treat estimates of overall survival. Adjustment methods include rank-preserving structural failure time models, inverse probability of censoring weights and two-stage approaches. NICE advises against simple censoring or excluding switchers, and its Decision Support Unit covers the methods in Technical Support Documents 16 and 24.

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U

Unanchored indirect comparison

A comparison of treatments from different studies without a common comparator, for example a single-arm trial against an arm of another study, so that randomisation is not preserved. Validity requires adjustment for all prognostic factors and effect modifiers, an assumption that is rarely verifiable. The HTA Coordination Group guideline describes unanchored MAIC and STC without a common comparator as highly problematic.

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Utility

A preference-based value for a health state on a scale where 1 is full health and 0 is death, with negative values possible for states considered worse than death. Utilities are usually obtained by applying a national value set to a generic instrument such as the EQ-5D, and are used as the quality weights in QALY calculations. NICE prefers utilities reported directly by patients and valued by a representative sample of the UK population.

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