N population size e Margin of error percentage in decimal form z z-score. To find the right z-score to use refer to the table below. If we are using three independent variables then a clear rule would be to have a minimum sample.
Using the formula above the required sample size per group is 90 and thus the total sample size required is 180.
Here is an example of how the math works assuming you chose a 90 confidence level 6 standard deviation and a margin of error confidence interval of - 4. Plug in your Z-score standard of deviation and confidence interval into the sample size calculator or use this sample size formula to work it out yourself. Necessary Sample Size Z-score2 StdDev 1-StdDev margin of error2. The formula does not cover finite population.