Population Count  
Expected Incidence Rate (%)  
Desired Precision Level (%)  
Confidence Level  
Sample Size  

Calculate a Statistical Sample Size - Attribute Sampling

This calculator allows you to estimate the random sample size required to achieve a specified level of statistical precision, or sampling error, in making a sample inference about a population. The required input parameters are: (1) the population count; (2) the estimated incidence rate of the attribute; and (3) your desired statistical precision, expressed as a percentage of the population at a specified confidence level.

How to Use

  1. Enter the Population Count.

  2. Enter the Estimated Incidence Rate (of that population). Expected Incidence rate must be greater than zero. In the case of a population of funded loans, the incidence rate may refer to the incidence of defective loans in the population. Since we cannot know the actual defect rate of the population (that's why we need to sample), this number must be an estimate. Because this is a important number, it should reflect your best estimate; if you are unsure what to enter, consider performing an initial pilot study with a small sample, then revisit the sample size calculation using the pilot study's incidence rate.

  3. Enter your Desired Precision Level and select a Confidence Level, either one-sided or two-sided. Precision Level must be greater than zero.

  4. After you have entered all values, click on the Calculate button. The System will calculate the sample size required to achieve the desired precision level. You may change the entered values and click the Calculate button again to perform the calculation based on the new values.