An intensive longitudinal study on interpretation issues with the PHQ instructions

Concerns have been raised that PHQ-9 instructions ("bothered by" symptoms) conflict with frequency-based response options, potentially leading to some patients experiencing difficulty mapping lived experience onto response options and may conflate frequency with burden. We tested whether weekly PHQ-9 scores aligned more with symptom frequency or burden using an intensive longitudinal design. Depressed patients (n = 23) reported daily symptom presence and burden (n = 1290 days) and completed weekly PHQ-9 (n = 236 weeks). Mixed-effects models decomposed within- and between-person effects and estimated patient-specific frequency-burden weights. Frequency and burden were highly correlated; each predicted PHQ-9 scores when modeled alone, but neither showed unique effects jointly. Thus, weekly PHQ-9 change may reflected a shared symptom-severity signal; person-level heterogeneity was suggested but uncertain. Findings are preliminary and should be interpreted alongside the PHQ-9's strong evidence base.