Performing Mixed Methods Research
There is a vast literature on mixed and multi-method research. This literature has many Similarities and Differences with the literature on interdisciplinarity.
There are two broad types of mixed and multi-method research:
Sequential Mixed Methods Research
Both of these types of research should be informed by an appreciation of the strengths and weaknesses of different methods as outlined in Classifying Methods It is critical to appreciate that all methods have strengths and weaknesses, and thus to strive to combine methods with compensating strengths. We must recall that all methods are biased, and thus no one method should be relied upon exclusively. An appreciation of the strengths and weaknesses of different methods guides not only the selection of methods but analysis of the results obtained, especially if different methods generate different results.
The core precept of mixed methods research is that each method is to be employed properly. Researchers should be familiar with best practices for each method employed.
The literature on transdisciplinarity speaks to how to mix methods in an interdisciplinary context: Transdisciplinary Insights
The National Institutes of Health (U.S.) has suggested best practices with respect to mixed methods research grants for both applicants and reviewers. See:
http://obssr.od.nih.gov/scientific_areas/methodology/mixed_methods_research/section7.aspx
Special note should be made of strategies for Complexity Analysis
The best source on mixed methods research is S. Hesse-Bulber and R.B. Johnson eds.,Oxford Handbook of Multimethod and Mixed Method Research, 2015..