Stephenson, W. (1935). Technique of factor analysis. Nature, 136(3438), 297-298.
Brown, S. R. (1980). Political subjectivity: Applications of Q methodology in political science. Yale University Press.
Watts, S., & Stenner, P. (2012). Doing Q methodology: Theory, method, and interpretation. Qualitative research in psychology, 9(4), 429-446.