Final answer:
The primary purpose of the Social Introversion Scale (Si) is to assess an individual's social introversion tendencies and preferences.
Step-by-step explanation:
The primary purpose of the Social Introversion Scale (Si) in psychological assessments is to assess an individual's social introversion tendencies and preferences. The Si is a self-report inventory that measures a person's level of social introversion by asking questions about their social interactions and preferences. It uses a scale to determine the degree to which someone is introverted or extroverted in social situations.