Time dependency of trade union membership

Event-history analysis is used to model the time dependency of two decisions: the decision to join a trade union, and the decision to leave a trade union. We formulate two hypotheses with regard to these two decisions and parametric regression models are used to investigate these hypotheses. The process of joining a trade union can be described by a decreasing rate, using a Weibull. For the process of leaving a trade union, we suggest an increasing rate that decreases after several years, a process best described by a log-logistic model.