|Item||Original domain (Humphrey et al) ||Rationale for removal|
|How much of the day were you unable to do things due to your fatigue?||Overall fatigue||
• The term “unable” appeared to target more severe fatigue only, based on qualitative feedback and a tendency towards a stronger floor effect than other items within domain.|
• Patients reported some confusion about how to answer, for e.g. often they could still do things, even if difficult.
• Redundant item, highly correlated with other items (all above 0.86 with other items from the global fatigue experience domain). This was the least clearly understood item.
|How much energy did you have today?||Characterizing fatigue||
• Performed poor psychometrically, low correlations with other items (0.177 to 0.339). Most likely due to the fact that it is the only positively stated item.|
• Interviews indicate “energy” may mean different things to different people (e.g. physical versus mental).
|How much did tiredness stop you from doing things today?||Activity limitations||• As with “unable”, the term “stop you” appeared to target more severe symptoms only, based on qualitative feedback and a tendency towards a stronger floor effect than other items within domain. All correlations above 0.944 with other items in the impact on function domain.|
|How tired did you feel when you woke up in the morning?||Characterizing fatigue||
• Intention of question was to capture “unrelenting fatigue not improved with sleep”, however not clearly interpreted as such.|
• Quantitative data suggested that question conceptually overlapped with separate concept of sleep quality rather than fatigue.
|How weak did you feel today?||Characterizing fatigue||
• Redundant with question about “how weak did your muscles feel today?” (correlation 0.967) This was the least clearly understood question.|
• Quantitative data suggested that this item was somewhat conceptually confusing.
|How much of the day did you feel overwhelmed by tiredness?||Characterizing fatigue||
• Interpreted as targeting more severe fatigue based on the qualitative feedback and a tendency towards a stronger floor effect than other items within domain.|
• Conceptually unclear. Some patients felt that the question was asking about an emotional component of fatigue.