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The Lick-index spectrophotometric system is investigated in its inherentstatistical and operational properties to ease a more appropriate use forastrophysical studies. Non-Gaussian effects in the index standardizationprocedure suggest that a minimum S/N ratio has to be reached by spectral data,such as S/N >= 5 px^{-1} for a spectral resolution R~2000. In addition, index(re-)definition in terms of narrow-band "color" should be preferred over theclassical pseudo-equivalent width scheme. The overlapping wavelength rangeamong different indices is also an issue, as it may lead the latter ones tocorrelate, beyond any strictly physical relationship. The nested configurationof the Fe5335, Fe5270 indices, and the so-called "Mg complex" (including Mg1,Mg2 and Mgb) is analysed, in this context, by assessing the implied bias whenjoining entangled features into "global" diagnostic meta-indices, like theperused [MgFe] metallicity tracer. The perturbing effect of [OIII](5007) and[NI](5199) forbidden gas emission on Fe5015 and Mgb absorption features isconsidered, and an updated correction scheme is proposed when using[OIII](5007) as a proxy to appraise Hbeta residual emission. When applied topresent-day elliptical galaxy population, the revised Hbeta scale leads, onaverage, to 20-30% younger age estimates. Finally, the misleading role of thechristening element in Lick-based chemical analyses is illustrated for thestriking case of Fe4531. In fact, while Iron is nominally the main contributorto the observed feature in high-resolution spectra, we have shown that theFe4531 index actually maximizes its responsiveness to Titanium abundance.

Lick-index entanglement and biased diagnostic of stellar populations in galaxies