I have seen that some electrical components (which contain R,L,C elements) datasheets shows the curve of the quality factor Q with respect to frequency, and not simply its value at the resonance frequency. For instance, this is the curve we find on this datasheet of an high frequency inductor:

Now, the definition of the quality factor is this one:

At resonance the energy stored in the equivalent RLC circuit of the component may be evaluated as the maximum energy stored in the inductance or also as the maximum energy stored in the capacitance during a period, since at resonance both quantities are equal. But how we evaluate the energy stored for a generic frequency? I'd say that in general, the energy stored in the magnetic field is different from that stored in the electric field, if we are not working at resonance.