Definition of the Shape Parameterγin the Interacting-Boson Model

It is argued that any estimate of the shape parameter $\gamma$ determined from interacting-boson-model (IBM) wave functions depends on the choice of $\chi$ in the definition of the IBM quadrupole operator $d_{\mu }^{†}s+s^{†}{\tilde{d}}_{\mu }+\chi {\left(d^{†}d\right)}_{2\mu }$. The consequences of different choices are discussed.