  One of the fundamental hypotheses in observational cosmology is the validity
of the so-called cosmic distance-duality relation (CDDR). In this paper, we
perform Monte Carlo simulations based on the method developed in Holanda,
Goncalves & Alcaniz (2012) [JCAP 1206 (2012) 022] to answer the following
question: what is the number of galaxy clusters observations N_{crit} needed to
check the validity of this relation at a given confidence level? At 2\sigma, we
find that N_{crit} should be increased at least by a factor of 5 relative to
the current sample size if we assume the current observational uncertainty
\sigma_{obs}. Reducing this latter quantity by a factor of 2, we show that the
present number of data would be already enough to check the validity of the
CDDR at 2\sigma.
