The recognized full-membership list by the USIA is from 2 sigma to 5 sigma, in which “sigma” applies to “S.D.” or standard deviation. For example, Mensa = 2 sigma (1:50 or 1-out-of-50 in the general population), when S.D. equals 15, 16, or 24 , means 3 times 15, 16, or 24, plus 100, or 130, 132, and 148, respectively. Please make sure the list is for the reference of the official USIA Qualifications.
| 2 Sigma (Standard) | |
| 132, SD16 | Mensa |
| 137, SD16 | Intertel |
| 137, SD16 | Top One Percent Society |
| 3 Sigma (Standard) | |
| 148, SD16 | Three Sigma Intelligence Society of USIA |
| 149, SD16 | Triple Nine Society |
| 150, SD16 | One in a Thousand Society |
| 4 Sigma (Standard) | |
| 164, SD16 | Four Sigma Intelligence Society of USIA |
| 164, SD16 | Prometheus Society |
| 164, SD16 | Epimetheus Society |
| 176, SD16 | Mega Society |
| 176, SD16 | Omega Society |
| 5 Sigma (Experimental) | |
| 180, SD16 | Esoteric Sigma Intelligence Society of USIA |
