Validating the 15-item stress anxiety depression scale (SAD-15) using Rasch analysis

Area of Science:

• Psychometrics
• Primary Care Research
• Mental Health Screening

Background:

• Stress, anxiety, and depression commonly co-occur in primary care settings.
• Current screening methods for these conditions are often separate, leading to inefficiencies.
• The Stress Anxiety Depression scale (SAD-15) was developed for simultaneous assessment of these three conditions.

Purpose of the Study:

• To evaluate the structural validity of the SAD-15 using Rasch measurement theory.
• To assess the clinimetric properties of the SAD-15 and its subscales.
• To determine the reliability and validity of the SAD-15 for primary care screening.

Main Methods:

• Rasch analysis was applied to data from 222 general practice patients.
• Key analyses included dimensionality, item/person fit, reliability, local dependency, and differential item functioning (DIF).
• Cut-off scores were identified using the WHO-5 Well-Being Index as a criterion.

Main Results:

• The full SAD-15 showed poor fit; however, composite scores demonstrated excellent Rasch fit and unidimensionality.
• High person separation reliability (PSI 0.77-0.93) and acceptable item/person fit were observed.
• No DIF was found across demographic groups, and optimal cut-offs were established.

Conclusions:

• The SAD-15 demonstrates potential as an efficient initial screening tool for stress, anxiety, and depression in primary care.
• Its composite structure is suitable for preliminary assessment before condition-specific evaluations.
• Further validation in diverse clinical populations and longitudinal studies is warranted.