  We aim to characterize the current status of knowledge on the accuracy of
open-cluster parameters such as the age, reddening and distance. These
astrophysical quantities are often used to study the global characteristics of
the Milky Way down to very local stellar phenomena. In general, the errors of
these quantities are neglected or set to some kind of heuristic standard value.
We attempt to give some realistic estimates for the accuracy of available
cluster parameters by using the independent derived values published in the
literature. In total, 6437 individual estimates for 395 open clusters were used
in our statistical analysis. We discuss the error sources depending on
theoretical as well as observational methods and compare our results with those
parameters listed in the widely used catalogue by Dias et al. (2002). In
addition, we establish a list of 72 open clusters with the most accurate known
parameters which should serve as a standard table in the future for testing
isochrones and stellar models.
