The rationale behind the development of the PAI was to create an assessment tool that would enable the measurement of psychological concepts while maintaining statistical strength.
The development methodology was based on several advances that the field of personality assessment was witnessing at the time.
Due to the fuzzy nature of constructs (concepts) in psychology, it is very difficult to use criterion-referenced approaches, such as those used in some parts of medicine (e.g. pregnancy tests).
The PAI was developed because the authors of the instrument felt that there were a limited number of self-report questionnaires that were using this type of construct validation method to assess areas relevant to diagnoses and treatment planning.
For example, the Depression scale has items involving physical, emotional, and cognitive content (as opposed to only questions about mood or interests).
As such, the developers of the PAI stressed the fact that their measure has no overlapping items to ensure better interpretation of the scales.
The initial items were written so that the content would be directly relevant to the different constructs measured by the test.