Treatment Switching
Treatment switching is when trial patients start a treatment they were not randomised to, typically control patients taking the new drug after progression.
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.
Truncation
Truncation occurs when people or values failing a selection rule are never recorded, as with late registry entry, and can bias survival and cost estimates.
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.
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.
Unit of Allocation
The unit of allocation is the patient, practice, hospital or other entity a trial randomises to each arm; the analysis must allow for that level.
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.
Variance
Variance is the average squared deviation from the mean, measuring spread in patient costs and outcomes and the uncertainty of health economic estimates.
Variance Inflation Factor
The variance inflation factor (VIF) measures how much overlap among predictors enlarges a regression coefficient's variance in cost or outcome models.
Varimax Rotation
Varimax rotation is an orthogonal factor rotation maximising the variance of squared loadings in each factor, used to find health questionnaire domains.
Verification Bias
Verification bias is error in estimated sensitivity and specificity when who receives the reference standard, or which one, depends on the test result.
Weighted Least Squares Regression
Weighted least squares (WLS) is regression that weights each squared residual, ideally by the inverse of its error variance, as in meta-analysis for HTA.
WEMWBS
WEMWBS is the Warwick-Edinburgh Mental Wellbeing Scale, a 14-item measure of positive mental wellbeing used as an outcome in public health evaluations.
WHOQOL-BREF
WHOQOL-BREF is the WHO's 26-item generic quality of life questionnaire with four domain scores, used as a trial outcome but not as a QALY utility.
Within Subject Variation
Within-subject variation is the scatter of one patient's repeated measurements, such as utility scores or costs, around that patient's own usual level.
WOMAC
WOMAC is a 24-question index of pain, stiffness and physical function in hip and knee osteoarthritis, used in trials and mapped to EQ-5D utilities.
Z-Score
A z-score is the number of standard deviations a value lies above or below a reference mean, used in health economics to compare outcomes on one scale.