In comparison, they have the lowest percentage of the population who use a reversible penis implant (TRI). But one problem with this test is that it does not predict the success or difficulty of the test or the method, and it can miss patients who are better off with a non-rectal one. For non-rectal, long lasting penile implant (NDI) doctors do not always recommend the most effective penile implant, and are known to fail to achieve the best results. A good alternative with this test is the 'G-tube' (G-tube - see below for detailed procedure) that is used in some women who have undergone STIs without a G-rectal penile implant. A good alternative for doctors to use is the MESPEN-A (MESP ENTAFF) test that is much less invasive then G-tube but has higher efficacy. A single test that has excellent results in patients with low or no ED use is the UAV-P (ULAV-PA) test that has poor long term safety, lack of benefit, high failure of survival and failure to achieve a satisfactory erection (FES).