Folding Back
The process of calculating a decision tree's expected values by working backward from final outcomes toward the initial decision node.
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.
Force of Infection
The rate at which susceptible individuals become infected, determined jointly by disease prevalence and the rate and probability of transmission per contact.
Fractional Polynomial
A flexible modelling technique representing a non-linear relationship using a small number of power transformations of a continuous variable.
Frailty Model
A survival model incorporating an unobserved random effect, called frailty, to represent risk heterogeneity not captured by observed covariates.
Gamma Distribution
A flexible probability distribution capable of representing increasing, decreasing, or constant hazard patterns, commonly used for time-to-event and cost data.
Gamma Model
A survival model assuming time-to-event data follow a gamma distribution, allowing hazard rates that increase, decrease, or stay constant over time.
Gaussian Process
A flexible statistical framework modelling an unknown function by treating any finite set of its values as jointly normally distributed.
Gaussian Process Regression
A non-parametric technique modelling an unknown function by treating any finite set of outputs as jointly normally distributed, giving predictions with uncertainty.
Gaussian Quadrature
A numerical integration technique approximating a definite integral using a weighted sum of function values at strategically chosen points.
Generalized F Model
A highly flexible parametric survival model encompassing several other distributions, including the exponential, Weibull, and log-normal, as special cases.
Generalized Gamma
A flexible probability distribution including the gamma, Weibull, and log-normal distributions as special cases, capable of representing many hazard shapes.
Generalized Gamma Model
A survival model based on the generalised gamma distribution, nesting simpler distributions, such as the Weibull and log-normal, within one framework.
Genetic Algorithm
An optimisation technique inspired by evolution that iteratively selects and combines the best candidate solutions across generations to improve results.
Gibbs Sampling
A Markov chain Monte Carlo algorithm generating samples from a complex joint distribution by iteratively sampling each variable from its conditional distribution.
Global Sensitivity Analysis
Sensitivity analysis techniques assessing how a model's output responds to simultaneous variation across the full range of all uncertain inputs, unlike one-way analysis.
Gompertz Distribution
A probability distribution characterised by a hazard rate rising exponentially with time, originally developed to describe human mortality increasing with age.
Gompertz Model
A survival model based on the Gompertz distribution, assuming the hazard rate rises exponentially over time, a pattern common in age-related mortality.
Goodness of Fit
A statistical measure of how well a model's predicted values correspond to observed data, used to assess whether it adequately fits the pattern.
Goodness of Fit Test
A formal statistical test determining whether observed data are consistent with a specified distribution or model, providing a basis for accepting or rejecting it.
Gradient Descent
An iterative optimisation algorithm adjusting parameters in the direction that most rapidly reduces an objective function until a minimum is reached.