Creswell, J. W. (2014) Research design : qualitative, quantitative, and mixed methods approaches (4th ed.) London: Sage Publications.
Understanding Research Methods (Coursera, free without certificate) by Dr J. Simon Rofe, SOAS, University of London & Dr Yenn Lee (University of London)
Questionnaire Design for Social Surveys (Coursera, free without certificate) by Dr. Frederick Conrad & Dr. Frauke Kreuter (University of Michigan)
Qualitative Research Methods (Coursera, free without certificate) by Dr. Gerben Moerman (University of University of Amsterdam)
We are happy to answer questions about research methods and assist with choosing a method that is right for your research.