How large should be a survey sample?
What survey sample size? A survey sample analysis helps using survey data appropriately so to make correct decisions.
There are 4 main methods to determine a survey sample size:
- Arbitrarily (what often happens with online surveys)
- Minimum cell size (Chi2)
- According to a desired precision
This last method depends on the population size the sample will be extracted from. The size of a sample extracted from an infinite population (larger than a million or so) is typically determined according to the following bernoullian formula, commonly used in marketing research:
Just a hint 384 interviews is the sample size of a survey conducted at 95% Confidence Interval and 5% Error level (the two values cannot be added together).
Special formula may apply in cases like lab tests without repetition, it means when the sample elements cannot be replaced in the population, for instance a Taste Test on biscuits.
Don’t waste time. Try MarketingStat’s Sample Size Calculator.
It prints nice reports, in pdf too, and it is completely free.
When the survey data was gathered arbitrarily (like most online surveys) you can still use MarketingStat’s free Sample Size Calculator to find the error level at which the survey was conducted. That’s useful information to make accurate confidence intervals.