This open access article from the Journal of Medical Internet Research features a comparison between two modes of questionnaire delivery: postal only, and mixed-method (email followed up by postal mail). The authors looked at:
Here are the conclusions:
“Mixed-mode surveys are an alternative method to postal surveys that yield comparable response rates and groups of respondents, at lower costs. Moreover, quality of health care was not rated differently by respondents to the mixed-mode or postal survey. Researchers should consider using mixed-mode surveys instead of postal surveys, especially when investigating younger or more highly educated populations.”
Zuidgeest, M., et al. “A Comparison of a Postal Survey and Mixed-Mode Survey Using a Questionnaire on Patients’ Experiences With Breast Care.” Journal of Medical Internet Research (JMIR):2011;13(3):e68.