Dear all,
How to calculate the sample size, for an online survey, of an unknown population regarding satisfaction with public health services? This is a situation where the last population census was conducted almost 10 years ago, but estimates point to 33 million as the overall country's population/inhabitants. There are no statistics about people's use of public health services. Physical access to people is made difficult due to the extension of the country and the bad quality of the roads. However, it is estimated that 21 out of 100 people use the internet.
Hello José,
Yes, planning and executing a survey can be a challenge, even in the best of circumstances.
The real question is, what is the target population?
One practical approach would be to obtain contact information for persons who have used public health services, say, within the past 60-90 days as your target population. Assuming that you have, or could legitimately obtain, access to this information, then the actual surveying might encompass multiple methods, including online (when valid email addresses exist), telephone (when valid numbers exist), or face-to-face (when valid addresses exist). Within each subset, you would randomly select whatever number of clients with whom to attempt contact.
Once populations reach, say, one million or more, the specific value makes little practical difference. Such differences won't have any appreciable effect on the requisite sample sizes in order to attain some target level of precision in any population estimates (assuming probability sampling methods).
In any event, the low internet use/access figure you cite makes it clear that any sample reached exclusively for an online survey is quite likely not to be representative of the country as a whole.
Good luck with your work.
Dear David,
I really thank you for your very insighful answer. It gives me lots of food for thoughts. I will keep the discussion going as I build the key elements of the research.
I wish you all the best with your work.
A good source for how to maximize response rates in online surveys is Dillman et al. Internet, Mail, and Mixed-Mode Surveys: The Tailored Design Method (4th ed.)
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