Motivated by results in Rotnitzky et al. (2000), a family of parametrizations of the location-scale skew-normal model is introduced,
and it is shown that, under each member of this class, the hypothesis H0: λ = 0 is invariant, where λ is the asymmetry parameter. Using the trace of the inverse variance matrix associated to a generalized gradient as a selection
index, a subclass of optimal parametrizations is identified, and it is proved that a slight variant of Azzalini’s centred
parametrization is optimal. Next, via an arbitrary optimal parametrization, a simple derivation of the limit behavior of maximum
likelihood estimators is given under H0, and the asymptotic distribution of the corresponding likelihood ratio statistic for this composite hypothesis is determined.