The (bio)psychosocial model for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) of Vercoulen et al . Fatigue: the subjective feeling of fatigue; fatigue subscale of the Checklist Individual Strength. Focusing on (Bodily) Symptoms: somatisation subscale of the Symptom Checklist. (Level of) Physical Activity: Sickness Impact Profile (SIP) subscale mobility (SIP-MOB) and the Physical Activities Rating Scale. (Functional) Impairment: impairment in daily life; subscale of activities at home of the SIP. Sense of Control (over Symptoms): selected items of the modified Pain Cognition List on a specific five-point scale. Causal Attributions: Causal Attributions List (high scores: physical attributions, low scores: psychosocial attributions).