Test-retest reliability of single-item assessments of immune fitness, mood, and quality of life.

The use of single-item assessments is increasingly important and popular, as these enable quick real-time assessments in clinical practice or research. In this study we investigated the test-retest reliability of single-item assessments of mood ("stress", "anxiety", "depression", "fatigue", "loneliness", "being active", "optimism", and "happiness"), quality of life, and immune fitness in N = 108 participants. The analysis revealed high test-retest correlations between the single-item assessments (r = 0.67 to 0.90), moderate to excellent intraclass correlations (r = 0.672 to 0.889), and the Bland-Altman analysis revealed agreement between all test-retest assessments, except for depression. Taken together, it can be concluded that the single-item assessments of mood, quality and immune fitness have a good test-retest reliability. This strengthens the rationale for using these single item assessments.