What is the % of a population that should be randomly tested for a scientific survey?

I need to take a random survey in our county. What percentage of the population should I ask in order to have an appropriate sampling?

What is the % of a population that should be randomly tested for a scientific survey?
Use this formula.


n=Z^2a/2/4E^2





n= sample size





Z^2a/2= your Z score, or area under the normal curve. Will depend on your confidence interval. Say, wanting 90% of data within 3 std of mean





4E^2 4 times acceptable error squared. Set error at 0.05, which is standard.





You need a Z score chart and a rudimentary knowledge of statistics, but this formula save much money on too large a sample size, or too small a size.
Reply:5% although there is no set number you need....
Reply:I would suggest around 5 to 10% of the 'available' population, but bear in mind that you need to sample people from various age groups, so you could be limited in an area that's dominated by very young, very old, or middle-aged people. It's all down to the law of averages.