Absolute Error
The absolute difference between an estimated or measured value and the true or accepted value.
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.
Absorbing State
A health state within a Markov model from which no further transitions are possible, most commonly death, once entered permanently.
Accelerated Failure Time
A class of survival models assuming covariates act multiplicatively on time itself, speeding or slowing progression to an event, unlike a Cox model.
Accuracy
A general measure of how closely a test result, measurement, or prediction corresponds to the true underlying value, covering sensitivity and specificity.
Active Choice
A choice architecture approach requiring an individual to make an explicit selection rather than passively accepting a default.
Activity-Based Costing
A costing method that assigns overhead and indirect costs to services based on the actual activities that consume resources, rather than a simple volume measure.
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.
Adverse Selection
Adverse selection occurs when people use private information about their risk before an agreement to make participation or contract choices, causing those who select into a market or plan to differ systematically from the wider population.
Age Weighting
An early methodological adjustment to the DALY calculation valuing healthy years lived in young to middle adulthood more highly than years in childhood or old age.
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.
Allocative Efficiency
A condition in which resources are distributed among competing uses to maximise total value, given fixed technical efficiency in production.
Alpha Spending
A group sequential trial method allocating the overall acceptable risk of a false positive across multiple planned interim analyses.
Annuity Payment
A reimbursement structure paying a treatment's total cost to the manufacturer in a series of instalments over time, rather than as a single upfront sum.
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
A summary statistic representing a predictive model's discriminative ability, the area beneath its ROC curve, from 0.5 for chance to 1 for perfect.
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.
Asymptotic Normality
A statistical property whereby, as sample size grows large, an estimator's sampling distribution approaches a normal distribution regardless of the original data's shape.
Atkinson Index
A measure of income or health inequality incorporating an explicit parameter reflecting society's aversion to inequality at the bottom of the distribution.