- Market survey
- One-on-one interviews
- Silent Observation (ethnography)
I am a firm believer that quantitative and qualitative research methods complement and strengthen each other.
It's hard to conduct a meaningful market survey without the benefit of some one-on-one interviews. It's also hard to understand the relative extent of problems uncovered in one-on-one interviews and ethnographic studies without a survey.
I also think that, if you have conducted sufficient qualitative research, you can draw reliable (yet somewhat subjective) conclusions from surveys even without a "scientifically valid" sample of responses.
Thus, in general, I believe it's important to conduct both quantitative and qualitative research regardless of the scope of a study. When scoping down, instead of eliminating one or the other methods, you're better off doing them all but doing less of each one.