0
$\begingroup$

I am currently using a formula I got from a Qualtrics blog post to calculate the sample I require for a survey for the mean to be meaningful/reflect the population mean, as follows:

https://i.sstatic.net/s7KAm.jpg

My survey has a large Std.dev (1.8), which I use instead of assuming a 0.5 Std.dev. This formula does not seem to take into consideration the population size (>10 000), however.

Is there an alternate formula to calculate required sample size with a known population size (but an unknown population std.dev)?

Improve this question
$\endgroup$

1 Answer 1

Reset to default
2
$\begingroup$

Population size is irrelevant unless the sample is a large portion of the population, which is clearly not the case here. There is a finite population correction: $FPC = \sqrt{\frac{N-n}{N-1}}$

where N is population size and n is sample size, but this is so close to 1 in your case that it can be ignored.

Improve this answer
$\endgroup$
3
  • $\begingroup$ Out of interest and possible future application, what would one then do with the FPC value (which in my case is 0,98)? $\endgroup$
    – The_Dude
    Commented Jul 24, 2017 at 12:39
  • $\begingroup$ One would multiply the sample size by its inverse. $\endgroup$
    – Peter Flom
    Commented Jul 24, 2017 at 12:49
  • $\begingroup$ So n * (1/FPC)? $\endgroup$
    – The_Dude
    Commented Jul 24, 2017 at 13:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.