I'm surveying a population of student in a university, and due to distance and time issues, I cannot go to every campus to survey everybody. This is why I have decided to do an online survey. So I got two options:
- I send an open invitation for every (or at least 99%) of the students, thus having the self-selection bias.
- I randomly pick everyone from a list and try to reach them through alternative means (like Facebook, e-mail, etc).
For option 1, I'll easily get a larger sample size (I guess around 400); for option 2, I believe I can reach a way shorter sample size (I guess around 100). I'm estimating according to the time I have.
So, in a 95% confidence level I could get a margin of error smaller than 5% in option 1, and around 10% in option 2. But in option 2 I won't have self-selection bias.
What option is the best? And why? Does anyone recommend me anything in a reliable literature source?