In general quantitative research is most valuable when it is used to investigate any behavior (or value or belief) that can be quantified without doing harm to the core concept that is being investigated. However, some concepts and behaviors are in fact very difficult to quantify. How, for example, can one quantity the idea of religious belief without coming up with a unit that is so far divorced from the idea of faith that the research design has destroyed its own subject? One of the problems that often comes up within research design is that some elements of a problem may be best assessed through quantitative means and others through qualitative means, which is why so many researchers favor multi-method approaches.
