One of the most complicated parts of a longitudinal data analysis is the interpretation of the regression coefficient. The regression coefficient is a weighted average of the between-subjects relationship and the within-subjects relationship. In Chapter 5, first hybrid models are introduced. Hybrid models are developed to disentangle the between- and within-subjects relationship. Hybrid models can be performed by calculating: (1) the individual average value of the covariate, which is used to obtain the between-subjects part of the relationship and (2) the deviation score, which is the difference between the observed values and the individual mean value and is used to obtain the within-subjects part of the relationship. In this chapter the modelling of changes and the autoregressive model are also discussed. Both models intend to estimate only the within-subjects part of the longitudinal relationship. All methods are accompanied by extensive real-life data examples.