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Table 1 Rationale for deleted items

From: Multidimensional daily diary of fatigue–fibromyalgia–17 items (MDF-fibro-17). part 1: development and content validity

Item Original domain (Humphrey et al) [14] 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.