“…In particular, dependency of observations may be seen as a clustering effect (Bergsma et al 2009) which arises in a number of sampling designs, including clustered, multilevel, spatial, and repeated measures (Heagerty et al 2000, Bergsma et al 2009, Geraci & Bottai 2014. In this context, quantile methods for modeling dependent-type data have been considered in a wide range of different applications spanning from medicine (Smith et al 2015, Farcomeni 2012, Alfò et al 2017, Marino et al 2018, Merlo, Maruotti & Petrella 2021, social inequality (Heise & Kotsadam 2015), economics (Bassett & Chen 2002, Kozumi & Kobayashi 2011, Bernardi et al 2015, Giovannetti et al 2018, Merlo, Petrella & Raponi 2021, environmental modeling (Hendricks & Koenker 1992, Pandey & Nguyen 1999, Reich et al 2011) and education (Kelcey et al 2019). When the interest of the research is on the entire conditional distribution, in addition to the classical quantile regression, a possible alternative approach is to consider the M-quantile regression proposed by Breckling & Chambers (1988).…”