What is the primary purpose of the five-tiered investigative model?

The primary purpose of the five-tiered investigative model is to conduct background investigations for security clearances. This model is designed to systematically evaluate an individual's reliability, trustworthiness, and loyalty to the United States, which are crucial factors when determining their eligibility for access to classified or sensitive information.

The five tiers represent varying levels of investigation based on the sensitivity of the position and the information an individual may access. This structured approach ensures that each person's background is thoroughly examined in relation to the level of clearance they require, thus maintaining national security and protecting sensitive information.

In contrast, the other options focus on functions that are not relevant to the core mission of the investigative model. Enhancing military training, assessing mental competency for federal employees, and regulating pay scales involve different aspects of personnel management and federal employment, which are outside the scope of the security clearance investigation framework.