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Sample Size Calculator
Significance
Survey Design
Correlation
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Sample Size Formulas

Here are the formulas used in our Sample Size Calculator:

Sample Size 

     ss = Z * (p) * (1-p)

c2

where:
     Z = Z value (e.g. 1.96 for 95% confidence level) 
p = percentage picking a choice, expressed as decimal
      (.5 used for sample size needed)
c = confidence interval, expressed as decimal 
      (e.g., .04 = 4)


Correction for Finite Population

      

ss

  new ss =
   
1+ ss-1

pop

where:
     pop = population


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