Dear Arkhawan,

The direct response to your question is, YES.

Case study research design accomodates a wide range of research methods - eclectic. This means that the selection of the various methods that the researcher wants to use should be purposive. Therefore, if you feel that the questionnaire will elicited certain information better than the other methods that you will be employing then go ahead. Remember that the point of selecting data collection methods is to help you answer the research question.

I am not sure I will classify a questionnaire as a quantitative data collection tool although one would observe that it is mostly employed to answer quantitative oriented research question. The questionnaire as a data collection tool could be used to collect data to answer qualitative oriented research question.

In any case, you could apply a mixed -methods approach to answer you research question. But you should be aware of all the epistemological debates around mixing methods.

Thank you very much Mr. Ferdinand . I appreciate your answer, it is very helpful to me.

Yes. It is possible to use questionnaire or other instrument to investigate these situations, however, doing some practical fieldwork, as part of a case study, will definitely go further in helping you best understand them.

Good luck..

Yes! You can. Answers by previous researchers are exhaustive

The following sources should also be helpful:

• Hancock, D. R. and Algozzine, B. (2006). Doing case study research: A practical guide for beginning researchers, New York, NY, Teachers College Press.
• Harrison, H., Birks, M., Franklin, R. and Mills, J. (2017). Case Study Research: Foundations and Methodological Orientations. Forum: Qualitative Social Research, 18, 1.
• Yin, R. K. (1981). The case study crisis: Some answers. Administrative science quarterly, 26, 1, pp. 58-65.
• Any advice between a case study or mixed methods design?: https://www.researchgate.net/post/Any_advice_between_a_case_study_or_mixed_methods_design

As everyone else has said before, Yes! I think having a questionnaire can help you strengthen the results you'd get from the two first methods. Your answers would then be of a deeper reach too since there are different levels/angles of answering to the same question. Good luck with the study!

Many thanks for all of you. I appreciate your valuable answers and guidance.

Yes, using mixed methods can enrich your data sets. It is a matter of what purpose you want to achieve with your case study. furthermore, it depends on the research questions. You stated that your field of research for the case study is language teaching methodology.

Thank you for your question and for incredible responses. This question is critical for so many students!