The first is simply to fit separate DREP models to each of several different sub-samples, where the sub-sample membership is defined by observable characteristics. ( This procedure allows all model parameters to differ between groups, not only A..) Examples of this strategy were discussed in Section 4.2. This is done by Andren and Andren (2013), and most systematically by Cappellari and Jenkins (2014) who interact every element of Z„_i with lagged SA receipt on the grounds that this allows each characteristic to have a different impact on rates of entry into and exit out of SA receipt.45 The same procedure is also commonly used to examine whether state dependence varies with calendar time (see e.g. Bhuller and Konigs (2011), Cappellari and Jenkins (2008a), and Konigs (2013a)). A third approach is to allow for unobserved heterogeneity in the state dependence parameter. For example, Stewart’s (2007) study of unemployment persistence considers the case in which dependence is normally distributed with a mean and variance estimated from the data.