Gay E.V.
Russian Federation State Scientific Centre — A.I. Leipunsky Institute of Physics and Power
Engineering, Obninsk, Russia
The onset of true PPP is considered, i.e., the effect that is not caused by misinterpretation
of incompletely documented experimental data. PPP is shown to be accompanied by an unexpectedly low
uncertainty associated with the least-squares method (LSM) estimate. This phenomenon is denoted the Small
Uncertainty Paradox (SUP). Two measurements are used to demonstrate that the occurrence of PPP and SUP
is conditioned by the presence of large values of the experimental systematic errors and by the significance
deviation of their shape from the shape of the assumed regression (model) function. An investigation is made
of the dependence of PPP and SUP on the value of the covariance for the experimental errors. SUP can occur
in nuclear data evaluation without the manifestation of PPP. Covariance (correlation) limitation is proposed
as a radical way of preventing these paradoxes. An estimate of the systematic error is considered as a possible
benefit if these paradoxes are true. The work is based on classical LSM; the Bayesian approach is not used.
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