Case study is not a qualitative study - it is a research
strategy which use qualitative and quantative data as well. You
select a data sources if it provides good arguments.
A case-control study is qualitative. This is because this kind
of study is an observational study, meaning that it involves
observing how groups differ in their behavior. The word qualitative
measures the quality of something rather than the quantity
(qualitative), meaning that a qualitative study measures their data
through characteristics rather than numbers.
How are qualitative and quantitative research alike?
For example, in qualitative research you resort to a case study approach, while in quantitative research you may resort to survey method. Quantitative research largely deals with volumes of data collected from primary or secondary sources. Qualitative research will focus on descriptions, contents, views, perspectives and its analysis.