TABLE 1.

Definitions and age requirements for variables in the study

Datapoint	Definitions	Age cut-offs if relevant, for confidence of diagnosis
Racial and ethnic categories Seizure types	According to United States National Institute of Health categories According to International League Against Epilepsy definitions16	N/A N/A
Epilepsy type	According to International League Against Epilepsy definitions of seizure types above including generalized types, focal types, both, or unknown	N/A
EEG encephalopathy patterns (burst suppression, hypsarrhythmia, generalized slowing with multifocal sharp waves, slow spike and wave with or without fast activity, electrical status epilepticus in sleep, othera)	On the basis of clinical EEG reports, with overall consistency with American Clinical Neurophysiology Society and International League Against Epilepsy guidelines. Electrical status epilepticus in sleep defined as spike wave index > 50%	N/A
Status epilepticus	Continuous seizure or back-to-back seizures without recovery lasting 30 minutes or longer19	N/A
Developmental and epileptic encephalopathy	A combination of infantile/childhood onset epilepsy (onset < 18 years), an encephalopathy pattern on EEG (as defined above), and developmental delay or intellectual disability15	≥1 year of age at last follow-up
Treatment-resistant epilepsy	Not responsive to two or more appropriately chosen antiseizure medications at therapeutic doses20	N/A
Sequential seizures (seizures with multiple phases)	A sequence of ictal patterns, motor or non-motor, not following an expected pattern of evolution based on spread (e.g. hypermotor–tonic–spasms sequence)26	N/A
Cerebral visual impairment	Visual dysfunction in the absence of ocular or anterior visual pathway abnormalities21	≥2 years of age at last follow-up
Microcephaly Macrocephaly	Head size > 2 standard deviations below the mean Head size > 2 standard deviations above the mean	N/A
Intellectual disability	DSM-5 criteria, as documented in clinical notes (not requiring neuropsychological evaluation)	≥5 years of age at last follow-up
Autism spectrum disorder	DSM-5 criteria, as documented in clinical notes (not requiring neuropsychological evaluation)	≥3 years of age at last follow-up

^aOther encephalopathy patterns on EEG included discontinuous patterns, abundant epileptiform activity (focal or generalized) not meeting criteria for electrical status epilepticus in sleep, and generalized slowing with poorly organized wake and/or sleep features.

Abbreviations: EEG, electroencephalogram; N/A, not applicable.