a – Quantitative study
A quantitative study is an analysis that measures the behavior or opinions of consumers (general public, decision-makers in companies, Internet users, etc.). … Quantitative studies are used by industries, traders, institutions (even associations) for a specific purpose.

b – Qualitative study
A qualitative study is most often carried out by collective (focus group) or individual interviews or by observations in situation carried out on small samples. … It generally aims to understand in depth attitudes or behaviors.