Modifiers matching difficulty:

• chronic,
• somatic,
• mechanical,
• psychological,
• emotional,
• unusual,
• logistical,
• economic,
• unforeseen,
• serious,
• temporary,
• sensory,
• physical,
• personal,
• interpersonal,
• periodic,
• progressive,
• psychiatric,
• financial,
• respiratory,
• significant,
• behavioural,
• spiritual,
• maternal,
• unanticipated,
• educational,
• secondary,
• possible,
• traditional,
• structural,
• stressful,
• past,
• technical,
• underlying,
• natural,
• invisible,
• local,
• common,
• minor,
• unexpected,
• visual,
• academic,
• typical,
• habitual,
• experienced,
• clinical,
• acute,
• home,
• surgical,
• functional,
• cognitive,
• environmental,
• conceptual,
• hormonal,
• real,
• parental,
• important,
• concurrent,
• everyday,
• legal,
• extra,
• major,
• internal,
• sexual,
• nutritional,
• domestic,
• neurological,
• anatomical,
• perceptual,
• linguistic,
• neuropsychiatric,
• leaning,
• severe,
• particular,
• behavioral,
• external,
• single,
• stable,
• technological,
• extraneous,
• experimental,
• related,
• reproductive,
• extreme,
• ongoing,
• motor,
• special,
• mathematical,
• developmental,
• smaller,
• mental,
• regulation,
• practical,
• operational,
• computational,
• social,
• prevalent,
• basic,
• commercial,
• persistent,
• administrative,
• subjective,

Simple categories matching persistent:

• substrate,
• discomfort,
• symptom,
• condition,
• distress,
• material,
• mineral,
• abnormality,
• dirt,
• information,
• infection,
• upset,
• pesticide,
• disease,
• disorder,
• herbicide,
• matter,
• instability,
• organism,
• pollutant,
• state,
• pain,
• lesion,
• difficulty,
• complaint,
• chemical,
• substance,
• aggression,
• virus,
• circumstances,
• injury,
• illness,
• insecticide,
• retrovirus,
• bacteria,
• organophosphate,
• metal,
• time,
• volatile,
• pathogen,
• headache,
• affliction,
• problem,
• compound,
• consequence,
• contaminant,
• cause,
• event,