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. 2015 May 8;3(2):e39. doi: 10.2196/mhealth.3879

Table 6.

Variance components for multi-item measures of the diary.

Source of variance Headache impactMIDASa % overall variance
Personb 0.060 27.91%
Dayc 0.002 0.93%
Itemd 0.017 7.91%
Person-by-daye 0.034 15.81%
Person-by-itemf 0.005 2.33%
Day-by-itemg 0.000 0.00%
Errorh 0.097 45.12%
Total 0.22 100.00%
Between Subjects Reliability (R1F)i 0.66
Between Subjects Reliability (RKF)i 0.98
Within Subjects Reliability (RC)i 0.51

aPedMIDAS measure was not explored due to the small sample size that completed this measure.

bPerson = variance due to between-person differences across all days and items.

cDay = variance due to differences between days across all persons and items.

dItem = variance due to responses to scale items across all persons and days.

ePerson-by-day = variance due to between-person differences at different days across all items.

fPerson-by-item = variance due to between-persons differences in responses to scale items across all days.

gDay-by-item = variance due to differences between days in responses to scale items across all persons.

hError = Person x Day x Item interaction plus random error (unknown sources of variance).

iR1F, RKF, and RC are forms of internal consistency calculated using formulas from Cranford et al (2006) [43].