The study uses qualitative interview data in order to trace the internal processes of interest organisations. The fourth chapter lines out the logic of the research design, case selection, methods and the data collection process. It provides details about interview partners and interview situations. The research project follows a most-different systems design in order to show that, across a set of least similar groups, the organisational structure affects interest groups in similar ways. The data of the project was collected during the period from April 2014 to September 2015.