This study also suggests a number of avenues for future computational studies. Firstly, analysis of the π-cubic phases of e.g. SnS and SnSe would confirm, or otherwise, that: (1) the size of the primitive cell, rather than the crystal symmetry, is the key predictor of low group velocities; and (2) that the local environment of the tetrel atoms, rather than the "global" crystal symmetry, is the key predictor of anharmonicity. Secondly, extension of this study to GeS and SnS, and to the Pb chalcogenides PbS, PbSe and PbTe, would provide a clearer picture of the role of the chalcogen and tetrel in defining the κ κ κ latt and would complement previous studies with new insight into the anharmonicity in the Pb chalcogenides. We aim to address both points in the near future.