Absorbing State
A health state within a Markov model from which no further transitions are possible, most commonly death, once entered permanently.
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.
Actuarial Method
A technique estimating survival probabilities by dividing follow-up into fixed intervals and calculating the proportion surviving each, accounting for those lost to follow-up.
Agent-Based Model
A simulation approach representing individual entities, such as patients or providers, as autonomous agents following behavioural rules, letting system patterns emerge.
Akaike Information Criterion
A statistic comparing the relative quality of candidate statistical models fitted to the same data, penalising those with more parameters.
Antithetic Variates
A variance reduction technique pairing each sampled value with a negatively correlated complementary value to reduce a simulation's output variance.
Area Under Curve Approach
A survival extrapolation method fitting a parametric distribution to observed data and calculating the area under the resulting curve to estimate mean survival.
Arrival Process
The pattern by which entities, such as patients, enter a discrete event simulation over time, governed by a probability distribution of intervals.
Background Hazard
The rate of death from causes unrelated to the disease under study, applied to represent risk a patient would face regardless of the condition.
Bathtub Hazard
A hazard pattern that is high early in follow-up, declines to a stable middle period, then rises again later, resembling a bathtub's shape.
Bayesian Analysis CEA
The application of Bayesian statistical methods to cost-effectiveness analysis, combining prior beliefs with observed trial data to produce posterior distributions.
Bayesian Information Criterion
A statistic comparing candidate models fitted to the same data, similar to the Akaike criterion but penalising complexity more as sample size grows.
Bayesian Optimisation
A statistical approach updating probability estimates as new evidence arrives, used to combine prior information with observed trial data in modelling.
Beta Distribution
A flexible probability distribution bounded between zero and one, commonly used to represent uncertainty in probability parameters.
Calibration
The process of adjusting a model's unobserved or uncertain parameters so its predicted outputs match observed real-world data as closely as possible.
Calibration Assessment
An evaluation of how closely a calibrated model's predicted outputs match the observed data used as calibration targets, typically using formal fit statistics.
Cause-Specific Survival
The probability of surviving without dying from a specific cause of interest, treating deaths from other causes as censoring rather than a competing risk.
Censoring
A situation in survival analysis where the exact time of an event is not observed, either because the study ended or follow-up was lost.
Chance Node
A point in a decision tree where the pathway followed is determined by probability rather than choice, branches summing to one.
Cholesky Decomposition
A matrix factorisation technique decomposing a covariance matrix to generate correlated random samples from otherwise independently sampled parameters.
Cohort Model
A decision-analytic model simulating the average experience of a defined group of patients moving through health states, rather than tracking each individually.