Cohen was reluctant to provide reference values for his standardized effect size measures. Although he stated that d = 0.2, 0.5 and 0.8 correspond to small, medium and large effects, he specified that these values provide a conventional frame of reference which is recommended when no other basis is available.

These stages postdate the Permo‐Carboniferous glaciation but retain a moderately steep equator‐to‐pole gradient, judging by the level of floral and faunal differentiation