Yes, Mill’s Most Different Systems Design (MDSD) is originally a comparative method from political science and is commonly used in quantitative research, but qualitative researchers can also apply its core logic when selecting cases.

Here’s how:

Mill’s Most Different Systems Design selects cases that are very different in most aspects, except for the outcome of interest, which is the same across all cases. The idea is that if very different cases all show the same outcome, then the factor(s) they have in common might explain that outcome.

In Qualitative Research:

You can absolutely use this principle to choose qualitative case studies. Here's how:

Select cases that differ in context (location, culture, size, etc.)

Ensure they share the same outcome (e.g., successful adoption of a farming practice)

Then, through in-depth interviews, observations, and document analysis, explore what common factors or mechanisms might be responsible for that outcome.

Why It Works Qualitatively:

It helps control for many alternative explanations by diversifying the background.

It enhances the analytical generalizability of your findings by showing that the same result happens under very different conditions.

It fits well with theoretical sampling in qualitative studies.

Example for Agriculture:

Let’s say we want to study why farmers adopt organic farming. You choose:

One farmer in a dry, poor area

One farmer in a fertile, high-tech area

One farmer from a tribal community Even though they are very different, if all adopted organic farming, you look for common motivations or support systems that led them to do so.

Thank you Badal Kailashbhai Koyani for your answer, it will be really helpful if you can provide the related reference.

I doubt if you are going to get any answers from an (uncredited) AI response. For sampling in comparative case studies, I recommend YIn's book, Case Study Research: Design and Applications.

Thank you David L Morgan , I will read Yin’s book.

Case selection shares similarities with but differ from qualitative sampling strategies, which are various types of purposeful sampling methods. For Yin, case selection focuses on two types: single case and multiple cases. Single case selection works pretty similar to selecting sample in other qualitative methods (e.g. extreme case, longitunial case, etc). Multiple case selection focuses on replication logics, including theoretical replication and literal replication. See the mentioned book by Yin for more information

Thank you Kien Nguyen-Trung for your explantation for case selection.