Simpson Paradox
A statistical phenomenon where a trend seen within subgroups reverses or disappears once those subgroups are combined into a single aggregated analysis.
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.
Simulated Treatment Comparison
A method comparing treatments from separate trials by fitting a regression model to one trial's data to predict outcomes for the other's population.
Skewness
A measure describing a distribution's asymmetry around its mean, positive skewness meaning a longer tail toward higher values.
Spearman Correlation
A non-parametric measure of the monotonic relationship between two ranked variables, calculated from data ranks rather than raw values.
Specificity
The proportion of individuals who truly do not have a condition who are correctly identified as negative by a diagnostic test.
Standard Deviation
A dispersion measure representing the average distance of data points from the mean, calculated as the square root of the variance.
Standard Error
A measure of an estimated parameter's precision, the standard deviation of its sampling distribution across repeated samples of the same size.
Standard Normal
A specific normal distribution with a mean of zero and standard deviation of one, used as a reference for standardising other variables.
Standardised Residual
A regression diagnostic dividing an observation's raw residual by its estimated standard deviation, allowing comparison on a common scale.
Statistical Power
The probability that a statistical test will correctly detect a true effect of a specified size, calculated as one minus the beta level.
Statistical Significance
A judgement that an observed result is unlikely to have occurred by chance under the null hypothesis, based on a p-value below a threshold.
Structural Equation Model
A modelling framework combining factor analysis and regression to test hypothesised relationships among observed and unobserved, latent variables.
Studentized Residual
A standardised residual excluding an observation's own contribution to the model fit, a more robust diagnostic for identifying influential data points.
SUCRA
An abbreviation for the surface under the cumulative ranking curve, ranking treatments in a Bayesian network meta-analysis by probability of being most effective.
Survival Regression
A modelling approach estimating the relationship between predictor variables and a time-to-event outcome, including the Cox model and parametric survival models.
Symptom-Free Survival
A time-to-event measure defined as the time from treatment start until the onset or return of clinically significant symptoms.
Synthetic Control
A quasi-experimental method constructing a weighted combination of untreated units to serve as a comparison group resembling a treated unit before intervention.
T-Distribution
A continuous probability distribution similar to the normal but with heavier tails, used when estimating a mean from a small sample with unknown variance.
Tau-Squared
A statistical parameter representing the estimated variance of the true treatment effect across studies in a random effects meta-analysis.
Taylor Series Expansion
A mathematical technique approximating a complex function using a polynomial series based on its derivatives at a single point, underlying the delta method.