Engel, C., Meisner, C., Wittorf, A., Wölwer, W., Wiedemann, G., Ring, C., Muche, R., & Klingberg, S. (2013). Longitudinal Data Analysis of Symptom Score Trajectories Using Linear Mixed Models in a Clinical Trial. International Journal of Statistics in Medical Research, 2(4), 305–315. https://doi.org/10.6000/1929-6029.2013.02.04.7