ABSTRACT
A "measurable" or "physical" quantity is a property of phenomena, bodies, or substances that can be defined qualitatively and can be expressed quantitatively. The true value of a measurable quantity would ideally reflect, both qualitatively and quantitatively, the corresponding property of the object. The theory of measurement relies on the following postulates: the true value of the measurable quantity exists; the true value of the measurable quantity is constant relative to the conditions of the measurement; the true value cannot be found. The measurement error must be evaluated by identifying its underlying sources and reasons and by performing computations based on the estimates of all components of the respective measurement inaccuracy. A statistical model comprises mathematical formulations that express the various outputs of a system in terms of probabilities. The first-order sensitivities contribute the leading terms to the second-, third-, and fourth-order moments of the response distribution, thus providing the leading contributions to the response's variance/covariances, skewness, and kurtosis.
