Hobbies And Interests
Data
Quantitative research produces quantifiable, reliable data that is the basis for all hard scientific knowledge. It has defined measurable facts you can use as baseline knowledge when applied to other areas of study. You can then use qualitative research to apply meaning to this data because quantitative research alone can't decontextualize the group or phenomena being studied.
Social
On social issues and issues of human psychology and thought, quantitative study can only provide a partial picture with statistics and facts. To seek to understand the "why" of societal issues and of human behavior, qualitative methods must be used. The use of interviews and focus groups, the study of writings and diaries -- these are qualitative methods of research that seek to gain and understanding of things to a further extent than quantitative research can go.
Prediction
Sometimes research is needed in order to predict certain behaviors or patterns, and it is this area where quantitative methods can be more effective than qualitative. Using large samples and observable, measurable experiments, you can use quantitative research to predict outcomes. For example, in traffic management where a new road is being proposed, quantitative research can demonstrate how motorists under certain conditions currently behave and you can use that knowledge to predict how they might behave under new conditions.
New Theory
When there is a lack of knowledge or information in an area such as a new branch of investigation or a pilot study, often it is the qualitative method that provides an overview of the subject with open conclusions. It does so before you can bring a more quantitative form of study to bear. Because qualitative data collection is unstructured and open-ended it is only with this method that people will gain a true overview of all issues involved with a new area of research.