making potential contamination a significant concern. For this reason, we therefore base our simulation on those fields for which the total extinction is less than $A_{V}$=0.45. A total of 35 fields had a column density less than our limit which corresponds to an area of 10 square degrees. We find eleven blue pulsators in these fields (these are flagged in the last column of Table 1).

Low resolution spectroscopic data exist for seven of these eleven pulsators and a spectroscopic analysis indicates they have a metal content consistent with that of SX Phe stars. Here we assume that all eleven pulsators at high Galactic latitudes are SX Phe stars. We use a simulation of the Galactic populations found in the fields to extrapolate the number of SX Phe stars found in the whole Galaxy. Our simulation uses a modified version of a model originally developed for populations of hot evolved stars (Napiwotzki 2008). Thin disc, thick disc and halo populations are included in our simulations, while the scale height adopted for the thick disk is 800 pc. The halo is modelled as an oblate ellipsoid with axis ratio $\epsilon$ = 0.76. Reddening is included in a simple approximation. Further details 