Investigation of methods for joint modelling of timing and intensity of accelerometry data

Music City Center 

Analysis of physical activity data from accelerometry is of great interest in the context of healthcare and quality of life. Moderate to Vigorous Physical Activity (MVPA) occurs in 'bouts' of continuous MVPA minutes. For these bouts, joint analysis of the intensity, which is a continuous variable, and the timing, which is a circular variable presents a unique challenge as the two measures constitute multi-modal data which requires sophisticated methods for analysis. Existing approaches transform the available polar coordinates to continuous rectangular coordinates that can be modelled using conventional methods, but the interpretation of results remains a challenge. We build upon existing methods by approximating the timing of a bout as a circular average of its constituent minutes, weighted by their intensity so as to better reflect the concentration of physical activity, and propose models for repeated measures analysis via Generalized Least Squares(GLS), Linear Mixed Effects(LME), and Bayesian Linear Mixed Effects(BLME). We compare the relative strengths and weaknesses of these models via simulation studies, and report results of their application to data from the NHANES cohort.

Moderate to vigorous physical activity

Joint modelling

Circular statistics

Bayesian

Longitudinal data

Repeated measures 

Biometrics Section