The number of methods used to study the properties of galaxies is increased , and testing these methods is very important .
Galactic globular clusters ( GCs ) provide an excellent medium for such test , because they can be considered as simple stellar populations .
We present ages and metallicities for 40 Galactic GCs as determined from three publicly available techniques , including colour , Lick-index and spectrum-fitting methods , based on Bruzual & Charlot evolutionary population synthesis ( EPS ) models .
By comparing with the ages obtained from colour-magnitude diagrams ( CMDs ) and metallicities obtained from spectra of stars , we are able to estimate the ability of these methods on determination of GCs ^ { { } ^ { \prime } } parameters , which is absolutely necessary .
As a result , we find that : ( i ) for the metallicity , our derived metallicities agree with those derived from the spectra of stars , Lick-index method is suitable to study metallicity for the stellar population systems in the range of -1.5 \la [ Fe/H ] \la - 0.7 and spectrum-fitting method is suitable to study metallicity for the stellar population systems in the range of -2.3 \la [ Fe/H ] \la - 1.5 ; ( ii ) for the age , these three methods have difficulties in age determination , our derived ages are smaller ( about 2.0 Gyr , on average ) than the results of CMDs for all these three methods .
We use Vazdekis and Maraston models to analyze whether our results are dependent on EPS models , and find that the tendency of these two models is the same as that of Bruzual & Charlot models .
Our results are independent of the EPS models .
In addition , our test is based on the old GCs and our conclusions may hold for old stellar population systems .

Besides the age-metallicity degeneracy , we examine the possible effects of other factors ( horizontal branch morphology , blue straggler stars , binary interactions and \alpha - enhancement ) and give quantitative analysis of the influences of these factors on age determinations ( except for \alpha - enhancement ) .
For colour and spectrum-fitting methods , the age can be underestimated about 0.0 - 3.0 Gyr , 0.0 - 2.0 Gyr , and 0.0 - 3.0 Gyr due to influences of horizontal branch , blue straggler and binary stars , respectively .
And for Lick-index method , the lower limit of maximal change of age is 6.0 Gyr , 5.0 Gyr and 3.0 Gyr due to influences of horizontal branch , blue straggler and binary stars , respectively .