Right Censoring
Right censoring occurs when follow-up ends before a patient's event, such as death, so the survival time is known only to exceed the last time observed.
Encyclopaedia
Explore comprehensive, evidence-informed explanations of key health economics concepts, including their development, application and relationships to other concepts. Published entries are validated through human expert review.
Concepts, entries and ontology terms
A concept page is a published entry on the wiki. Some concepts also have a full encyclopaedia article. The Health Economics Ontology (HEO) holds every concept, including dictionary terms without an article, so it is larger than the list of published pages. The knowledge graph shows how concepts relate to each other.
Robust Optimisation
An optimisation approach that selects a feasible decision to perform well under the worst parameter values in a specified uncertainty set, often requiring constraints to hold throughout that set.
Royston-Parmar Model
The Royston-Parmar model is a parametric survival model that fits splines in log time to the log cumulative hazard, used to extrapolate survival in HTA.
Scenario Analysis
Scenario analysis re-runs a health economic model under alternative assumptions, such as another survival extrapolation, to see if the decision changes.
Schoenfeld Residual
A Schoenfeld residual is the observed minus expected covariate value at each event in a Cox model, used to test the proportional hazards assumption.
SEIR Model
The SEIR model is a transmission model that adds an exposed, not yet infectious stage to the SIR model, used to evaluate vaccines and outbreak control.
Sensitivity Analysis
Sensitivity analysis tests whether a health economic model's results and decision change when uncertain inputs, assumptions or model structure are varied.
Sequential Analysis
Sequential analysis tests trial or safety data as they accumulate and stops once preset evidence boundaries are crossed, not at a fixed sample size.
Sequential Monte Carlo
Sequential Monte Carlo (SMC) tracks a sequence of probability distributions with weighted samples to calibrate health models and update them with data.
Shared Frailty
Shared frailty is an unobserved random effect, shared by all patients in a cluster such as one hospital, that scales their hazard in survival analysis.
Simpson Rule
Simpson rule is a closed Newton-Cotes numerical integration formula that approximates a definite integral over pairs of equal subintervals by integrating quadratic interpolants through successive triples of function values.
Simulated Annealing
Simulated annealing is a stochastic search method, used to calibrate health economic models, that sometimes accepts a worse fit to escape local optima.
SIR Model
The SIR model is an epidemic model that sorts people into susceptible, infectious and recovered groups, used in health economics to value vaccination.
Sobol Indices
Sobol indices are variance-based sensitivity measures giving the share of a health economic model output's variance due to each input and its interactions.
Sobol Sequence
A Sobol sequence is a deterministic low-discrepancy sequence that spreads parameter values evenly for quasi-Monte Carlo runs of health economic models.
Spline Model
A spline model is a regression model that joins polynomial pieces at knots to fit a flexible curve, such as hospital cost by age or survival over time.
State Occupancy
State occupancy is the expected time a modelled cohort spends in a health state, found by adding the share of the cohort in that state across model cycles.
State Reward
A cost, utility, health outcome, or other consequence accrued while a modelled person occupies a specified state for a defined amount of time.
State Space Model
A state space model is a time series model where hidden states, such as disease severity or service demand, evolve over time and are measured with error.
State Transition Model
A state transition model is a decision model in which a cohort or simulated patients move between health states over time to estimate costs and QALYs.