# Sample size calculation in two different population for administration of a questionnaire

I need some help calculating a sample size. I have two groups of people to whom I need to fill out a questionnaire. Group A consists of 45,000 people and group B consists of 3,000 people. How do I know what is the right sample size for group A and group B? Thank you very much in advance!

• Hello Egn! It's quite impossible to say without knowing what you want to measure or compare, you need to provide much more information than that. May 30 at 15:34
• Thank you for your answer! It is a questionnaire on the use of a drug to be submitted to Italian and Albanian doctors. The Italian doctors total 45,000 while the doctors in Albania total 3000. Now I wonder, how many Italian doctors should I submit the questionnaire to and how many to Albanian doctors? Thank you very much.
– Egn
May 31 at 10:30
• If you want to compare if they answer differently to a yes/no question, the calculation for the required sample size may be different than if you need to compare, let's say, how many times they prescribe the drug during a given year. In short, we need more information about the variables you want to analyze - e.g. if they are categorical (if so, how many levels?), ordinal, continuous, etc., and the kind of statistical test you plan to use. May 31 at 10:52
• By the way, if you want you can edit your post to make all these information more visible, rather than giving them in the comment section. May 31 at 10:52
• Also, I assumed that you want to compare Italian to Albanian doctors, but if comparison is not your goal, you should mention what you are looking for. May 31 at 11:06