DillmanD. A.SmythJ. D., & ChristianL. M. (2009). Internet, mail, and mixed-mode surveys: The tailored design method.Hoboken, NJ: Wiley.
2.
JohansonG. A., & BrooksG. P. (2010). Initial scale development: Sample size for pilot studies. Educational and Psychological Measurement, 70(3), 394–400.
3.
NunnallyJ. C., & BernsteinI. H. (1994). Psychometric theory (3rd ed.). New York, NY: McGraw-Hill.
4.
WillisG. B. (2005). Cognitive interviewing.Thousand Oaks, CA: Sage.