Survey Sample Size Calculator Example
Sample Size Example 1
Large Population: The population of Scotland is 5,313,600 (Mid 2102 stats). The survey needs to represent the full population with a confidence level of 95% (the level most researchers are willing to accept), allowing for a margin of error of 5%; the recommended sample is 369 responses. However, should the margin for error acceptable be 2%, the sample size would be 2304.
Sample Size Example 2
Smaller Population: A company has a database of 350 and wants to conduct a Customer Satisfaction Survey and needs to know the minimum number of responses they need to obtain a representative report. Again, a 95% confidence level is acceptable and a margin of error is 5%; the sample size will be 184.
Confidence Level
The confidence level is the amount of uncertainty you can tolerate. This will calculate how confident you want to be that the actual mean falls within your confidence interval. The most common confidence intervals are 90% confident, 95% confident and 99% confident. Higher confidence level requires a larger sample size. Margin of Error As no sample is ever going to be perfect, you should decide how much error to allow.
The confidence interval determines how much higher or lower than the population mean you are willing to let your sample mean fall. For Example; if you decided on a margin of error of 5 and one of your questions resulted in a rating of 85%; you will have a margin of error of +/ 5%. Response Distribution If you ask a random sample of 10 people if they use Facebook, and 9 out of 10 say "Yes", then the prediction that you make about the general population is different than it would be if 5 had said, "Yes", and 5 had said, "No".
If you don’t understand response distribution, you are best to leave it at the default of 50% as it is the more conservative assumption.
Survey Sample Size Calculator
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