Table 1 Rationale for deleted items
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. |