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Abstract A survey of even–even nuclei in the nuclear chart showed regularities in the values of the ratio Q (2 1 +) / (B (E 2) for each nucleus for which independent measurements of both the electric quadrupole moment of the 2 1 + state, Q (2 1 +) , and the reduced transition probability B (E 2 ; 0 1 + → 2 1 +) exist. As predicted by the rotational model, this ratio was found to be close to unity for the deformed nuclei in the rare-earth region. For non-rotational nuclei the absolute value of this ratio is almost always considerably lower. This latter observation can be interpreted within different models for different classes of nuclei as illustrated by a set of schematic IBA model calculations. A general mixing model and simple geometrical models are also suitable for collective non-rotational nuclei. Near magic nuclei a mechanism within the seniority scheme is compatible with the observed small value of R Q B. [ABSTRACT FROM AUTHOR]