Tragedy of the Commons
The tragedy of the commons is the overuse of a shared resource, such as antibiotic effectiveness, when each user keeps the gain but the cost falls on all.
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.
Transient State
A transient state is a health state in a Markov model that patients eventually leave for good, possibly after several stays, unlike an absorbing state.
Transition Matrix
A transition matrix is the table of probabilities of moving between, or staying in, health states in one cycle of a Markov model, with rows summing to one.
Transition Probability
A transition probability is the chance of moving from one health state to another, or staying, during one cycle of a Markov or state-transition model.
Transmission Model
A transmission model is an infectious disease model in which infection risk depends on how many people are infectious, so evaluations count herd effects.
Trapezoidal Rule
The trapezoidal rule approximates a definite integral by replacing a curve with straight-line segments and summing the resulting trapezoid areas.
Treatment Sequence Model
A treatment sequence model is a decision model comparing ordered pathways of therapies, moving patients to the next line when a treatment fails or stops.
Tunnel State
A tunnel state is one of a fixed sequence of one-cycle temporary states in a Markov model, letting risks, costs or utilities vary with time in a state.
Two-Way Sensitivity Analysis
Two-way sensitivity analysis varies two inputs of a health economic model together over a grid of values to show which combinations change the decision.
Type I Error
A type I error is a false positive in hypothesis testing, rejecting a null hypothesis that is true, such as concluding that an ineffective treatment works.
Type II Error
A type II error is a false negative in hypothesis testing, when a study fails to reject a false null hypothesis and misses a real treatment effect.
Unbiasedness
Unbiasedness is the property of an estimator, such as a trial's mean cost, whose average over repeated samples equals the true value it estimates.
Uncertainty
Uncertainty in health economics is imperfect knowledge of a model's true inputs, structure or methods, so the option chosen as best may prove to be wrong.
Uncertainty Quantification
Uncertainty quantification (UQ) measures how uncertainty in a health economic model's inputs and structure carries into its costs, QALYs and decision.
Uniform Distribution
The uniform distribution gives equal density to every value between two bounds and is used in health economic models for inputs known only by their range.
Unimodal Hazard
A unimodal hazard is an event rate that rises to a single peak and then falls, as log-logistic and log-normal survival models allow in HTA.
Unmarketed Good
An unmarketed good is an economic good, such as health or clean air, that is not traded in markets, so no market price shows its value in appraisal.
Unstructured Correlation
Unstructured correlation lets each trial visit have its own variance and each pair of visits its own correlation in models of repeated utilities or costs.
Utility Function
A utility function gives each outcome a number so that preferred outcomes score higher; in health economics it values health states, survival and income.
Utility Maximisation
Utility maximisation is the assumption that a person chooses the affordable option they rank highest, the basis of health economic models of demand.