Table 2.

Selected features from different layers of the classifier.

Layer	Selected features
First (migraine classifier) 32 features	Mode of onset: gradual (1st), female sex (2nd), absence of lacrimation (3rd), nausea/vomiting, headache triggered by upset stomach, not located in the temple, photophobia, absence of conjunctival injection, absence of brainstem aura: vertigo, ear fullness/tinnitus, not located in the vertex, headache-related disability in daily routines, absence of headache attack during sleep, aggravation by physical activity, not in location: all over the head, not in location: back of the head, osmophobia, not in location: retroauricular, head motion-induced worsening, phonophobia, no pulsating nature, throbbing nature, no stabbing nature, absence of motion sickness, absence of agitation, vertigo, headache-associated ocular pain, nature of pain: vague/cloudy, dull-ache-like nature, general weakness, not in location: forehead, dizziness
Second (TTH classifier) 19 features	Mode of onset: gradual (1st), nature of pain: vague/cloudy (2nd), cognitive complaint during headache attack (3rd), hypertension, absence of head motion-induced worsening, absence of avoidance of physical activity, nature of pain: dull-ache, no jabbing nature, nature of pain: drumming, absence of headache-induced awakening during sleep, nature of pain: pulsating, nausea/vomiting, headache attack in the afternoon, absence of headache-associated ocular pain, absence of aggravation by physical activity, absence of ocular pain, absence of disability in daily routines, female sex
Third (TAC classifier) 6 features	Headache attack during sleep (1st), headache triggered by upset stomach (2nd), conjunctival injection (3rd), location: periocular, lacrimation, male sex
Fourth (Epicranial headache classifier) 22 features	Location: retroauricular (1st), nature of pain: electric shock-like (2nd), nature of pain: jabbing (3rd), absence of headache triggered by upset stomach, no explosive nature, no tightening nature, no drumming nature, mode of onset: gradual, allodynia, nature of pain: tingling, absence of alleviation by sleeping, nature of pain: stabbing, location: temple, absence of aggravation by physical activity, nature of pain: vague/cloudy, no dull-ache-like nature, absence of ocular pain, photophobia, absence of nausea/vomiting, nature of pain: twinge, absence of headache-associated gastrointestinal discomfort
Fourth (TCH classifier) 22 features	Not in location: retroauricular (1st), no electric shock-like nature (2nd), no jabbing nature (3rd), headache triggered by upset stomach, nature of pain: explosive, nature of pain: tightening, nature of pain: drumming, mode of onset: thunderclap, absence of allodynia, no tingling nature, alleviation by sleeping, no stabbing nature, not in location: temple, aggravation by physical activity, no vague/cloudy nature, nature of pain: dull-ache, ocular pain, absence of photophobia, nausea/vomiting, no twinge nature, headache-associated gastrointestinal discomfort

The features listed in the right column positively correlated with the target subtype listed in the left column.

TTH tension-type headache, TAC trigeminal autonomic cephalalgia, TCH thunderclap headache.