It’s a dangerous mistake to believe that statistical research is somehow more scientific or credible than insight-based observational research. In fact, most statistical research is less credible than qualitative studies. Design research is not like medical science: ethnography is its closest analogy in traditional fields of science. —Jakob Nielsen —Risks of Quantitative Studies (Alertbox)
Note… he’s specifically talking about research into design — he’s not saying qualititaive research is always better than quantitative research.