Utilization of sub-milliarcsecond trigonometric parallaxes shifts the classical problem of calibration of stellar parameters to a new level of complexity. Derivation of stellar luminosity from the parallaxes is not a straightforward task with a number of statistical effects, such as Malmquist bias, to be taken into account. Different methods are to be used in order to derive parameters of luminosity function depending on the nature of underlying stellar sample. It is emphasized that any combination of astrometric parameters (i.e. parallaxes) and astrophysical ones must be handled carefully to avoid or reduce statistical effects, which otherwise may seriously affect the astrophysical applications.