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How to select the sample? (How is a probabilistic sample selected?…

- - - - pilot study:To test the validity of the questionnaire, it applies to a small sample. From this small sample,
        the standard deviation of the quantity is calculated and this value is used as the standard deviation of the population.
        
        comparative study: Apply this approach when a dispersion estimator from another study is available.
        
        approach based on the interval: To apply this approach you need to know or count on a calculation of the maximum and minimum values of the population.
- - - - n is the sample size.
      - z is the standard normal value corresponding to the desired confidence level.
      - or is the standard deviation of the population.
      - E is the maximum permissible error.
      - The result of this calculation is not always a whole number. When the result is not an integer, it is customary to round up any fractional result. For example, 201.21 would be rounded to 202.