See instructions below chart.
Calculate Sample Size (95% CI) for Required Precision
| Estimated Standard Deviation: | |
| Required precision: | |
| Population size (optional): | |
| Required sample size: |
Calculate Precision from Affordable or Known Sample Size Sample Size (95% CI)
| Standard Deviation: | |
| Sample Size: | |
| Precision: |
Calculate Sample Size (95% CI) for Required Precision
| Estimated Proportion Defective: | |
| Required precision: | |
| Required sample size: |
Calculate Precision from Affordable or Known Sample Size Sample Size (95% CI)
| Proportion Defective: | |
| Sample Size: | |
| Precision: |
If you don’t have any data yet, use the top part of the tool. Start by collecting a small sample of 10 or more for continuous data, 50 or more for proportion data. Calculate the standard deviation or proportion defective as appropriate. Then use the tool to determine the sample size you need to achieve your desired precision. The data used for your initial small sample becomes part of the total sample. When you’ve completed your sample, calculate standard deviation/proportion and use the bottom half of the tool to check the precision you have actually achieved.
If you have data, calculate the standard deviation or proportion as appropriate. Use the bottom part of the tool to determine the precision. If the precision is too large, use the top part of the tool to see how much more data you need to collect to achieve your desired precision.
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