The integration of qualitative and quantitative research - theoretical foundations of "mixed methods"

Mixed Methods have been used in social research for quite a long time, as can be seen by looking on influential empirical studies from the first half of the 20(th) century, where the combined use of qualitative and quantitative methods was justified in most cases only pragmatically (if at all). Unfortunately, the discussions led from the 1970s onwards about theoretical justifications of mixed methods designs often suffered from a focus limited on formal and epistemological issues. This holds true for the debates about the notion of "triangulation" as well as for the controversies about the paradigms presumably underlying quantitative, qualitative or mixed methods research. By contrasting "positivism", "constructivism" and "pragmatism" outdated frontlines were often preserved and complex philosophical problems oversimplified. Furthermore, the focus on epistemology led to a neglect of substantial issues relating to the research field (which are always critical for the use of methods). The necessity for using (and combining) quantitative and qualitative methods follows from the nature of social structures relevant for the concrete field of investigation which may differ widely according to their stability and flexibility. Thereby structures with limited scope or "contingent structures" create specific problems for qualitative and quantitative methods which can be detected and dealt with by drawing on the strengths of the respective other methodological tradition in mixed methods designs.