Quantitative & qualitative

The difference between quantitative and qualitative research does not only lie in the research method. It also has to do with the goal of the research. In a qualitative research the importance of 'why-aspects' predominate, whereas in quantitative research the generalizability of the results is more important. When posing a why question, every answer will be different, making it difficult to apply the result to an entire population. Defining response categories beforehand makes it easier to make such a generalization. But if the underlying reasons are more important, qualitative research is more convenient. 

In practice qualitative and quantitative research complement each other very well. First researchers often conduct a preliminary quantitative survey, after which (large-scale) quantitative research follows. Another common practice is that the research begins with a quantitative research, followed by an advances qualitative research. In short, the two forms coexist and definitely don't exclude each other.