In general, qualitative research generates rich, detailed and valid process data that contribute to the in-depth understanding of a context. Quantitative research, on the other hand, generates reliable population-based and generalizable data that is suited to establishing cause-and-effect relationships. The decision of whether to choose a quantitative or a qualitative design is ultimately a philosophical question. Which methods to choose will depend on the nature of the project, the type of information needed the context of the study and the availability of resources (time, money, and human).
In summary, a qualitative research question mainly focuses on “W” questions; distributions across or within large populations are of lesser importance and often cannot be examined due to the nature of qualitative research itself. The question should not be too broad, but also not too narrow. And you should be able to examine it at all. A prerequisite is that you can gain access to the field. You may have formulated a perfect qualitative research question, if putting it into practice requires talking to all ministers in your country and you do not have the right connections, your project cannot be realized. Before you continue to invest a lot of time and effort in a research idea, check out whether you can find participants. Talking to pupils in schools often takes a long process of getting permissions from the school board; you cannot just go to a schoolyard and talk to kids there. Military institutions are another case, where you need to adhere to specific procedures to be allowed access. Recently some students wanted to interview people that have converted to Islam, but were not able to find individuals that were willing to participate. Others were interested in people that are addicted to sports; they ended up changing their topic as they did not manage to get contact with such persons. In qualitative research terms, they could not access the field. Thus, there are not only institutional hurdles to overcome. It is probably easiest to find participants for your research, when the research question is based on your personal background or related to your social context. In other cases it is not impossible, but more difficult.