Method: The participants in this study were part of a larger study examining the relationships of lifestyle factors with mammographic breast density. The women were asked to wear the ActivPal monitor for 7 consecutive days during waking hours, removing only when bathing or getting in contact with water for extensive periods of time. To be included in this study, participants needed to have at least 10 hours of data for all 7 days. Sixty eight women were included in this analysis. Generalizability theory analysis was performed to determine the reliability of sitting time using the Generalized Analysis of Variance (GENOVA) software. Generalizability Theory is divided into two parts. The G-study which can quantify the percent of variance associated with each facet and its interactions. For the G-study, participant (P) and day (D) were considered random facets in a fully crossed design (PxD).The D-study provides a Generalizability coefficient (G) which can be interpreted like an ICC value. With the D-Study, it is possible to determine the measurement model needed to achieve a recommended reliable estimate G≥0.80.
Analysis/Results: The G-study results demonstrated that the largest source of variance in the model was the participants (P), accounting for 51% of the variance. Days (D) accounted for only 1%. The PxD interaction was responsible for 48% of variability reflecting the different relative standings of participants across days related to the amount of time spent sitting. Four days was enough to achieve a reliable estimate G≥0.80, 9 days were necessary for an estimated coefficient >0.9, and an estimated G=0.97 was achieved with 30 days of measurement.
Conclusions: The findings of this study demonstrated that the average sitting time can be assessed to a desirable reliability level (G≥0.80) with as little as 4 days of monitoring using the ActvPal, a valid device for measuring postural allocation.