Taylor Series Method
The practical application of a Taylor series expansion to derive an approximate variance formula for a function of random variables.
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.
Test Statistic
A single numerical value calculated from sample data during a hypothesis test, used to judge whether to reject the null hypothesis.
Test-Retest Reliability
The degree of agreement between scores from the same instrument given to the same people on two separate occasions, when no real change is expected.
Time-to-Event Analysis
Statistical methods analysing data on the time until a specific event occurs, such as death, while appropriately handling censored observations.
Tolerance Interval
An interval calculated to contain a specified proportion of an entire population's values with a given confidence, unlike a confidence or prediction interval.
Trajectory Analysis
A statistical approach identifying and characterising distinct patterns of change in an outcome over time, often revealing subgroups with different courses.
Treatment Effect
The change in an outcome attributable to a specific treatment, distinguished from changes that would have occurred regardless due to other factors.
Truncation
A situation in survival or longitudinal analysis where certain observations are systematically excluded based on a variable's value, such as required registration.
Two-Stage Meta-Analysis
An individual patient data meta-analysis first analysing each study separately, then combining the resulting study-level estimates using standard methods.
Two-Tailed Test
A hypothesis test assessing evidence for an effect in either direction, without specifying in advance whether it is expected to be better or worse.
Type I Error
In hypothesis testing, the error of incorrectly rejecting a true null hypothesis, concluding a genuine effect exists when it does not.
Type II Error
In hypothesis testing, the error of failing to reject a false null hypothesis, concluding no effect exists when a genuine effect is present.
Unbiasedness
A property of an estimator whose expected value, across repeated samples, equals the true underlying value of the parameter being estimated.
Uniform Distribution
A probability distribution in which every value within a defined range is equally likely to occur.
Unstructured Correlation
A correlation structure for repeated measures allowing the correlation between every pair of time points to be estimated freely and independently.
Variance
A dispersion measure representing the average squared deviation of individual data points from the mean of a dataset.
Variance Inflation Factor
A regression diagnostic quantifying how much an estimated coefficient's variance is inflated by correlation with other predictors, higher values meaning worse multicollinearity.
Varimax Rotation
An orthogonal factor rotation maximising the variance of squared loadings within each factor, tending to make each variable load strongly on only one factor.
Within Subject Variation
The degree to which repeated measurements on the same individual fluctuate over time, unlike between-subject variation reflecting differences across individuals.
Working Correlation
In generalised estimating equations, an assumed correlation structure among repeated observations, improving statistical efficiency even if not perfectly correct.