  The role of radial velocity (RV) jitter in extrasolar planet search surveys
is discussed. Based on the maximum likelihood principle, improved statistical
algorithms for RV fitting and period search are developed. These algorithms
incorporate a built-in jitter determination, so that resulting estimations of
planetary parameters account for this jitter automatically. This approach is
applied to RV data for several extrasolar planetary systems. It is shown that
many RV planet search surveys suffer from periodic systematic errors which
increase effective RV jitter and can lead to erroneous conclusions. For
instance, the planet candidate HD74156 d may be a false detection made due to
annual systematic errors.
