  Establishing the reliability with which stellar population parameters can be
measured is vital to extragalactic astronomy. Galactic GCs provide an excellent
medium in which to test the consistency of Single Stellar Population (SSP)
models as they should be our best analogue to a homogeneous (single) stellar
population. Here we present age, metallicity and $\alpha$-element abundance
measurements for 48 Galactic globular clusters (GCs) as determined from
integrated spectra using Lick indices and SSP models from Thomas, Maraston &
Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to
independent determinations we are able to assess the ability of these SSPs to
derive consistent results -- a key requirement before application to
heterogeneous stellar populations like galaxies.
  We find that metallicity determinations are extremely robust, showing good
agreement for all models examined here, including a range of enhancement
methods. Ages and $\alpha$-element abundances are accurate for a subset of our
models, with the caveat that the range of these parameters in Galactic GCs is
limited. We are able to show that the application of published Lick index
response functions to models with fixed abundance ratios allows us to measure
reasonable $\alpha$-element abundances from a variety of models. We also
examine the age-metallicity and [$\alpha$/Fe]-metallicity relations predicted
by SSP models, and characterise the possible effects of varied model horizontal
branch morphology on our overall results.
