  The knowledge of the orbit or the ephemeris uncertainty of asteroid presents
a particular interest for various purposes. These quantities are for instance
useful for recovering asteroids, for identifying lost asteroids or for planning
stellar occultation campaigns. They are also needed to estimate the close
approach of Near-Earth asteroids, and subsequent risk of collision. Ephemeris
accuracy can also be used for instrument calibration purposes or for scientific
applications. Asteroid databases provide information about the uncertainty of
the orbits allowing the measure of the quality of an orbit. The aims of this
paper is to analyse these different uncertainty parameters and to estimate the
impact of the different measurements on the uncertainty of orbits. We
particularly deal with two main databases ASTORB and MPCORB providing
uncertainty parameters for asteroid orbits. Statistical methods are used in
order to estimate orbital uncertainty and compare with parameters from
databases. Simulations are also generated to deal with specific measurements
such as future Gaia or present radar measurements. Relations between the
uncertainty parameter and the characteristics of the asteroid (orbital arc,
absolute magnitude, ...) are highlighted. Moreover, a review of the different
measuments are compiled and the impact of these measures on the accuracy of the
orbit is also estimated.
