and references therein].

For 44 out of the 48 UGSs, that have been analyzed on the basis of the above statistical methods, it is also possible to perform a comparison with our results to verify if the 2FGL sources that we associated to a $\gamma$-ray blazar candidates have been also classified as AGNs following the Ackermann et al. (2011b) procedures. By comparing the results of our association method with those in Ackermann et al. (2011b), we found that 27 out of 44 UGSs that we associate to a $\gamma$-ray blazar candidate are also classified as AGNs, all of them with a probability higher than 71% and 18 of them higher than 80%. Among the remaining 17 out of 44 sources, 7 have been classified as pulsars, with a very low probability with respect to the whole sample; in particular, 3 of these pulsar candidates are classified with a probability lower than 41% and all of them lower than 71%, making these classifications less reliable than those of the AGNs. The last 10 UGSs did not have a classification in Ackermann et al. (2011b). Consequently, we emphasize that our results are in good agreement with the classification suggested previously by Ackermann 