PEM Duration. Three additional PEM items within the DSQ examined duration of symptom exacerbation after activity. Participants were initially asked two questions: “Do you experience a worsening of your fatigue/energy related illness after engaging in minimal physical effort” and “Do you experience a worsening of your fatigue/energy related illness after engaging in mental effort”. If participants answered ‘yes’ to either of these questions, they were then presented with a question measuring PEM duration: “If you feel worse after activities, how long does this last”. Participant responses of PEM duration were coded as: 0 =
Not having a problem with energy/fatigue, 1 =
1 h or less, 2 =
2–3 h, 3 =
4–10 h, 4 =
11–13 h, 5 =
14–23 h, and 6 =
24 h or more. Both branching logic questions of symptom exacerbation due to physical activity (
k = 0.84) and symptom exacerbation due to mental activity (
k = 0.74) have good test-retest reliability [
7].