In 1978 two Jungian analysts, June Singer and Mary Loomis, initiated an innovative experiment with approximately 200 people. Being deeply concerned about the lifelong process of individuation, they were skeptical of any assumption that implied individuals remained the same throughout their lifetime. Consequently, they decided to empirically test the viability of the bipolar assumption underpinning the existing Jungian Type inventories (The Myers-Briggs Type Indicator and the Grey-Wheelright Type Inventory). Their experiment is described in detail in the Journal of Analytical Psychology (1980). The experiment involved creating new versions of each of these inventories by removing the forced-choice, either/or structure and, without changing the text of the items, placing each item on a Likert 5-point scale. Subsequently, they administered the original and the modified, non-bipolar versions to two groups totaling approximately 200 people.

The core difference between the original and the modified version was that the original assumed the presence of the bipolar condition, whereas the modified version did not. The modified version did not preclude showing the bipolar condition, if it was actually present. This allowed the presence or absence of the condition to become an empirically testable question rather than an untested assumption. Comparison of the results generated by the original and alternative versions of each of the inventories revealed that the forced-choice structure was creating inappropriate classifications of the dominant Type capacity in over 50% of the cases and of the least developed Type capacity in 40% of the time.

These startling results were far in excess of what could be reasonably expected if the forced choice structure (which was based on the bipolar assumption) was only a minor or insignificant issue. These results provided a compelling incentive to create a new Type inventory. When it was created in 1979, they called the new instrument the Singer-Loomis Inventory of Personality™(SLIP™).Over the course of the next four years, it was evolved from Version 1 to Version 3. Consulting psychologists published Version 3 from 1984-1995.

In early 1996, Drs. Singer and Loomis purchased the copyright from Consulting Psychologists Press and established an arrangement whereby, Drs. Elizabeth and Larry Kirkhart became the copyright holders and publishers of the Inventory and all associated materials. In March 1996, Elizabeth and Larry created a new organization, Moving Boundaries inc, dedicated to the further development of Jungian Type concepts and Jungian psychology in clinical and human resource development (HRD) areas. Moving Boundaries follows and supports American Psychology Association guidelines on the ethical and professional use of psychological instruments.

Creating Version 4

With the aid of professional colleagues and three Jungian analysts, June Singer, Mary Loomis and Martha Newell, Elizabeth and Larry Kirkhart thoroughly revised the instrument and created Version 4 in March 1996. At that time the inventory was renamed the Singer-Loomis Type Deployment Inventory™(SL-TDI™). In addition to changing existing items and situations, major changes were made in how the results of the Inventory were compiled and represented. The creation of Version 4 emphasized strengthening technical performance, increasing user friendliness and enhancing usability of the results.

Once the new version was available, field-testing was initiated immediately. Moving Boundaries now has over 3300 protocols in its database. A Cronbach Alpha analysis has been performed on 2684 cases. This analysis indicated that Version 4 Alpha scores were even higher than Version 3 on 14 of 16 outcome measures and that the SL-TDI meets or exceeds the levels of reliability expected of a personality inventory.
A summary of an independent study by members of the Psychology Department at Texas A&M shows similar results.