RESUMEN
Sudden gains (SGs), referring to large, stable symptom improvement occurring between consecutive treatment sessions, have been associated with improved outcomes among adults with various psychological disorders. Little research exists on SGs or sudden symptom worsening (i.e., sudden regressions [SRs]) during treatment for youth disorders. The current study examined predictors and outcomes of SGs/SRs via multiple informants in youth anxiety treatment. Participants were 118 youth (age M = 11.6, SD = 2.5; 53.8% female) and their caregivers receiving a cognitive-behavioral therapy protocol for a principal anxiety disorder. Anxiety symptom severity was assessed weekly via the State-Trait Anxiety Inventory for Children-Trait-Child/Parent versions. SGs and SRs occurred in 45.8 and 31.3% of youth, respectively. SRs were more common among youth with comorbid mood or externalizing disorders, while SGs occurred more often among youth with greater pretreatment anxiety symptom severity. SGs were not associated with posttreatment outcomes, but SRs predicted significantly higher posttreatment internalizing symptoms based on child report (ß = .23, p = .03) and externalizing symptoms based on child (ß = .15, p = .04) and parent report (ß = .16, p = .03), controlling for overall magnitude of symptom change. SRs among youth receiving cognitive-behavioral therapy for anxiety are associated with pretreatment clinical complexity and poorer posttreatment outcomes and may serve as a warning sign to clinicians of possible treatment failure.