Agree to Disagree: Reliability of Seizure Frequency Assessments

Epilepsia . 2026 Mar;67(3):1317-1331. doi: 10.1111/epi.70031. Epub 2025 Nov 30. Objective: Although vagus nerve stimulation (VNS) is a well-established neuromodulation therapy for drug-resistant epilepsy, treatment outcomes remain heterogeneous. One possible source of variability lies in differing interpretations of seizure frequency ratings (SFRs). This study examined interrater reliability (IRR) in SFRs between (1) retrospective clinician–clinician chart reviews and (2) prospective caregiver–clinician reports, and explored sources of disagreement. Methods: Data were collected from the CONNECTiVOS database. In the retrospective cohort ( n = 254), 2 clinicians independently reviewed medical records and rated seizure frequency across multiple timepoints. In the prospective cohort ( n = 214), caregivers and clinicians independently reported SFR in children treated with VNS. IRR was assessed across different measurement thresholds, and potential causes of disagreement were analyzed. Results: Clinician–clinician agreement in retrospective chart reviews was excellent (intraclass correlation coefficient [ICC] > .90, Cohen κ > .80), with 18.8% divergent ratings and 4.8% exceeding the reliable change index. Disagreement was significantly associated with higher mean seizure frequency at baseline ( P = .004) and at postoperative timepoints ( P < .001). In the prospective caregiver–clinician comparison, agreement for absolute seizure frequency was poor (ICC < .50), with discrepancies in 86.5% of cases, although only 1.8% were statistically significant. When rating pairs diverged, clinicians more often reported lower absolute seizure frequencies ( P = .002) and greater relative seizure reductions ( P = .023) and were more likely to classify patients as achieving a 90% reduction ( P = .043). Significance: This study highlights interrater variability in both retrospective and prospective SFR assessments, a finding systematically related to baseline seizure frequency. Coarser classifications (eg, 50% or 90% seizure reduction) may improve agreement but reduce clinical nuance. Future efforts should focus on structured, patient-centered documentation and the development of objective outcome measures in VNS evaluation, particularly for children with high seizure burden.