Regression Analysis
Statistical techniques modelling the relationship between one or more predictor variables and an outcome variable, from simple linear to survival regression.
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.
Relapse-Free Survival
A time-to-event measure defined as the time from treatment completion until disease recurrence or death, used for curative-intent treatments.
Relative Risk
A measure calculated as the ratio of the risk of an outcome in an exposed or treated group to that in an unexposed group.
Relative Risk Reduction
The proportional reduction in risk associated with a treatment, calculated as one minus the relative risk, expressed as a percentage.
Repeated Measures Analysis
A statistical approach analysing data in which the same outcome has been measured multiple times on the same individuals, accounting for correlation.
Reproduction Number
A general term for the average number of secondary infections one infected individual produces, covering both the basic and effective reproduction numbers.
Residual
The difference between an observed value and the value predicted for it by a fitted statistical model.
Risk Difference
The absolute difference between the risk of an outcome in one group and in another, the excess or reduced risk from an exposure.
Risk Ratio
A measure calculated as the ratio of risk in one group compared to another, synonymous with relative risk for event comparisons.
Robust Standard Error
An estimate of a regression coefficient's statistical uncertainty that remains valid even when standard modelling assumptions, such as constant error variance, are violated.
ROC Curve
A graph depicting the trade-off between a test's true positive rate and false positive rate across a full range of decision thresholds.
Root Mean Square Error
A measure of average prediction error, the square root of the average squared difference between predicted and observed values, in the outcome's units.
Sample Size Calculation
The process of determining the number of participants a study needs to have an adequate chance of detecting a specified treatment effect.
Sample Size Optimisation
The process of determining the number of trial participants needed to reliably detect a treatment effect of a specified, meaningful size.
Sandwich Estimator
A method calculating an estimator's variance that remains valid even when standard model assumptions are violated, forming the basis of robust standard errors.
Secondary Attack Rate
A measure of infectious disease transmission, the proportion of susceptible close contacts of a primary case who themselves become infected.
Selection Model
A missing data modelling approach explicitly modelling the process by which observations become missing, alongside the model for the outcome itself.
Sensitivity
The proportion of individuals who truly have a condition who are correctly identified as positive by a diagnostic test.
Sequential Sampling
A data collection approach in which the decision to continue or stop sampling is made based on accumulating data, rather than a fixed sample size.
Significance Level
The predetermined probability threshold, usually five percent, used to judge whether a result counts as statistically significant.