| year of publication | ISBN | author(s) | title |
|---|---|---|---|
| 2000 | 978-1-881773-01-6 | Patrick J. Aspell · Dee Dee Aspell | Enneanalysis (TM) |
| '' | 978-1-881773-05-4 | Patrick J. Aspell | The Enneagram Inventory® (Christian Version) |
| '' | 978-1-881773-09-2 | Dee Dee Aspell · Patrick J. Aspell | Aspell Type and Style Indicator |