Personality Assessment is a proficiency in professional psychology that involves the administration, scoring, and interpretation of empirically supported measures of personality traits and styles in order to:

• Refine clinical diagnoses;
• Structure and inform psychological interventions; and
• Increase the accuracy of behavioural prediction in a variety of contexts and settings (e.g., clinical, forensic, organisational, educational). (APA)

Most personality assessment instruments are in fact introspective (i.e., subjective) self-report questionnaire measures or reports from life records  such as rating scales.