Statistics

Physics

Statistical physics

Mathematical analysis

Visual arts

Estimation theory

Estimator

Nuisance parameter

Event (particle physics)

Applied mathematics

Mathematics

Logarithm

Astrophysics

Maximum likelihood

Musical

Restricted maximum likelihood

Formalism (music)

Likelihood function

The European Physical Journal C

Parameter estimation via unbinned maximum likelihood fits is central for many analyses performed in high energy physics. Unbinned maximum likelihood fits using event weights, for example to statistically subtract background contributions via the sPlot formalism, or to correct for acceptance effects, have recently seen increasing use in the community. However, it is well known that the naive approach to the estimation of parameter uncertainties via the second derivative of the logarithmic likelihood does not yield confidence intervals with the correct coverage in the presence of event weights. This paper derives the asymptotically correct expressions and compares them with several commonly used approaches for the determination of parameter uncertainties, some of which are shown to not generally be asymptotically correct. In addition, the effect of uncertainties on event weights is discussed, including uncertainties that can arise from the presence of nuisance parameters in the determination of sWeights .

Parameter uncertainties in weighted unbinned maximum likelihood fits