  Source position time series produced by International VLBI Service for
Geodesy and astrometry (IVS) Analysis Centers were analyzed. These series was
computed using different software and analysis strategy. Comparison of this
series showed that they have considerably different scatter and systematic
behavior. Based on the inspection of all the series, new sources were
identified as sources with irregular (non-random) position variations. Two
statistics used to estimate the noise level in the time series, namely RMS and
ADEV were compared.
