If one is looking at financial vulnerability of commercial banks to risks, then a quantitative longitudinal approach could work bcause there is access to time series data for several years. However, if it is at household level, then focus groups or face-to-face interviews suffices and more into qualitative research approach.

It depends on the factors like at which level you want to study and the nature of data you are searching for. If it is on macro level, I believe an quantitative approach would be apt, where as if it is on household basis, an qualitative case study approach will be better. Similarly, if it is a data that is too personal to the responsdent (which is mostly true in financial studies) an qualitative approach will be appreciated. If it is some data that the respondent is not hesitant to respond, quantitative approach will be apt.

Thank you.

PK

Might this help you get an overview?

https://www.researchgate.net/publication/317135305_Review_of_Financial_Vulnerability_Studies