Root Mean Square Error
The square root of the mean squared difference between numerical predictions and their corresponding observed values, expressed in the outcome’s original units.
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.
Sample Size Calculation
Sample size calculation sets how many participants a trial must analyse to detect a target clinical or economic difference at set power and significance.
Sandwich Estimator
The sandwich estimator is a variance formula for regression estimates that stays valid when cost data are heteroskedastic or patients are clustered.
Screening
Screening is the process of identifying apparently healthy people at increased risk of a condition, then offering information, further tests or treatment.
Secondary Research
Secondary research is research that summarises existing studies instead of collecting new data, as in systematic reviews and meta-analyses.
Selection Model
A selection model handles missing trial data by modelling the outcome alongside the chance each value is observed, allowing for data missing not at random.
Sensitivity
The proportion of people with a specified target condition who test positive at a stated diagnostic threshold, calculated as true positives divided by true positives plus false negatives.
SF-12
SF-12 is a 12-item generic health survey taken from the SF-36 that gives physical and mental summary scores and can be scored as SF-6D utilities for QALYs.
SGRQ
SGRQ is the St George's Respiratory Questionnaire, a weighted 0 to 100 measure of health impairment in COPD and asthma, used in trials and mapped to EQ-5D.
Short Physical Performance Battery
Short Physical Performance Battery (SPPB) is a timed test of balance, gait speed and chair stands in older people, scored 0 to 12, used in trials.
Significance Level
The significance level is a prespecified upper bound on the probability that a valid statistical test rejects its null hypothesis when that hypothesis is true.
Simpson Paradox
Simpson's paradox occurs when a treatment comparison that holds in every patient subgroup reverses or disappears once the subgroups are pooled together.
Simulated Treatment Comparison
Simulated treatment comparison (STC) is an HTA method that uses one trial's patient data to predict outcomes in another trial's population for comparison.
Six-Minute Walk Test
Six-minute walk test (6MWT) is a performance outcome that records distance walked in six minutes, used as an endpoint in heart and lung trials and in HTA.
Skewness
Skewness measures the asymmetry of a distribution around its mean, such as the long right tail that a few very costly patients give health care cost data.
Spearman Correlation
Spearman correlation is a rank-based measure from -1 to +1 of how consistently two variables, such as disease severity and costs, rise or fall together.
Specificity
Specificity is the share of people without the target condition whom a diagnostic test correctly calls negative, setting how many false positives arise.
Standard Deviation
Standard deviation is a measure of how widely patient costs, outcomes or other values spread around their mean, in the same units as the data.
Standard Error
The standard error (SE) is the standard deviation of an estimate's sampling distribution, showing how precisely a mean cost or treatment effect is known.
Standard Normal
The standard normal distribution is a normal distribution with mean 0 and standard deviation 1, used in health economics to read z values as probabilities.