  We define a method for analysis of the integrated spectra of extra-galactic
globular clusters that provides more reliable measures of age, metallicity and
alpha-element abundance ratio than have so far been achieved. The method
involves the simultaneous fitting of up to 25 Lick indices in a
chi-squared-fitting technique that maximises the use of the available data.
Here we compare three sets of single stellar population (SSP) models of Lick
indices to the high signal-to-noise, integrated spectra of 20 Galactic globular
clusters. The ages, [Fe/H] and alpha-element abundance ratios derived from the
SSP models are compared to the results of resolved stellar population studies
from the literature. We find good consistency with the published values, with
an agreement of better than 0.1 dex in all three derived parameters. The
technique allows identification of abundance ratio anomalies, such as the known
nitrogen over-abundance in Galactic globular clusters, and the presence of
anomalous horizontal-branch morphologies. It also minimises the impact on the
derived parameters of imperfect calibration to the Lick system, and reduction
errors in general. The method defined in this work is therefore robust with
respect to many of the difficulties that plague the application of SSP models
in general, and is, consequently, well suited to the study of extra-galactic
globular cluster systems.
