For this purpose a short overview about important methodological discussions addressing basic questions of mixed (qualitative and quantitative) method designs will be given focusing on the term "triangulation" which is seen by many authors as a central concept for method integration.
However, this notion carries systematic ambiguities, at least when transferred to the integration of qualitative and quantitative methods—triangulation does not represent a single integrated methodological concept but a metaphor with a broad semantic field.
A further goal is tob ring the case study to closure by writing a compelling report or book.
Triangulation involves using multiple data sources in an investigation to produce understanding.
Some see triangulation as a method for corroborating findings and as a test for validity. This assumes that a weakness in one method will be compensated for by another method, and that it is always possible to make sense between different accounts. Rather than seeing triangulation as a method for validation or verification, qualitative researchers generally use this technique to ensure that an account is rich, robust, comprehensive and well-developed.
Also be aware of tha fact that different social science research methods fill different needs and situations for investigating social topics.
A case study is relevant the more your research questions seek to explain some present circumstances: how and why some social phenomenon works or if your research questions require an “in-depth” sedcription of some social phenomenon.
This is where the concept of “triangulation” comes into its own.